Chapter 5. The IoC container

Chapter 5. The IoC container

As can be seen in the above image, the Spring IoC container consumes some form of configuration metadata; this configuration metadata is nothing more than how you (as an application developer) inform the Spring container as to how to “instantiate, configure, and assemble [the objects in your application]”. This configuration metadata is typically supplied in a simple and intuitive XML format. When using XML-based configuration metadata, you write object definitions for those object that you want the Spring IoC container to manage, and then let the container do it's stuff.

	Note
	XML-based metadata is by far the most commonly used form of configuration metadata. It is not however the only form of configuration metadata that is allowed. The Spring IoC container itself is totally decoupled from the format in which this configuration metadata is actually written. Attribute based metadata will be part of an upcoming release and it is already part of the Spring Java framework.

Spring configuration consists of at least one object definition that the container must manage, but typically there will be more than one object definition. When using XML-based configuration metadata, these object are configured as <object/> elements inside a top-level <objects/> element.

These object definitions correspond to the actual objects that make up your application. Typically you will have object definitions for your service layer objects, your data access objects (DAOs), presentation objects such as ASP.NET page instances, infrastructure objects such as NHibernate SessionFactories, and so forth. Typically one does not configure fine-grained domain objects in the container, because it is usually the responsibility of DAOs and business logic to create/load domain objects.

Find below an example of the basic structure of XML-based configuration metadata.

<objects xmlns="http://www.springframework.net">

  <object id="..." type="...">
    <!-- collaborators and configuration for this object go here -->
  </object>

  <object id="...." type="...">
    <!-- collaborators and configuration for this object go here -->
  </object>
 
  <!-- more object definitions go here -->

</objects>

It is often useful to split up container definitions into multiple XML files. One way to then load an application context which is configured from all these XML fragments is to use the application context constructor which takes multiple resource locations. With an object factory, an object definition reader can be used multiple times to read definitions from each file in turn.

Generally, the Spring.NET team prefers the above approach, assembling individual files because it keeps container configuration files unaware of the fact that they are being combined with others. However, an alternate approach is to compose one XML object definition file using one or more occurrences of the import element to load definitions from other files. Any import elements must be placed before object elements in the file doing the importing. Let's look at a sample:

<objects xmlns="http://www.springframework.net">

  <import resource="services.xml"/>
  <import resource="resources/messageSource.xml"/>
  <import resource="/resources/themeSource.xml"/>

  <object id="object1" type="..."/>
  <object id="object2" type="..."/>

</objects>

In this example, external object definitions are being loaded from 3 files, services.xml, messageSource.xml, and themeSource.xml. All location paths are considered relative to the definition file doing the importing, so services.xml in this case must be in the same directory as the file doing the importing, while messageSource.xml and themeSource.xml must be in a resources location below the location of the importing file. As you can see, a leading slash is actually ignored, but given that these are considered relative paths, it is probably better form not to use the slash at all. The contents of the files being imported must be fully valid XML object definition files according to the XSD, including the top level objects element.

• A type name: typically this is the actual implementation class of the object being defined..

• Object behavioral configuration elements, which state how the object should behave in the Spring.NET IoC container (i.e. prototype or singleton, lifecycle callbacks, and so forth)

• references to other objects which are needed for the object to do its work: these references are also called collaborators or dependencies.

• other configuration settings to set in the newly created object. An example would be the number of threads to use in an object that manages a worker thread pool, or the size limit of the pool.

Every object has one or more ids (also called identifiers, or names; these terms refer to the same thing). These ids must be unique within the container the object is hosted in. An object will almost always have only one id, but if an object has more than one id, the extra ones can essentially be considered aliases.

When using XML-based configuration metadata, you use the 'id' or 'name'attributes to specify the object identifier(s). The 'id' attribute allows you to specify exactly one id, and as it is a real XML element ID attribute, the XML parser is able to do some extra validation when other elements reference the id; as such, it is the preferred way to specify an object id. However, the XML specification does limit the characters which are legal in XML IDs. This is usually not a constraint, but if you have a need to use one of these special XML characters, or want to introduce other aliases to the object, you may also or instead specify one or more object ids, separated by a comma (,), semicolon (;), or whitespace in the 'name' attribute.

Please note that you are not required to supply a name for a object. If no name is supplied explicitly, the container will generate a unique name for that object. The motivations for not supplying a name for a object will be discussed later (one use case is inner objects).

When creating an object using the constructor approach, all normal classes are usable by and compatible with Spring. That is, the type being created does not need to implement any specific interfaces or be coded in a specific fashion. Just specifying the object type should be enough. However, depending on what type of IoC you are going to use for that specific object, you may need to create a default constructor (i.e. a constructor that has no parameters) in the source code definition of your class.

The XmlObjectFactory implementation of the IObjectFactory interface can consume object definitions that have been defined in XML, for example...

<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary"/>

The mechanism for supplying arguments to the constructor (if required), or setting properties of the object instance after it has been constructed, is described shortly.

This XML fragment describes an object definition that will be identified by the exampleObject name, instances of which will be of the Examples.ExampleObject type that has been compiled into the ExamplesLibrary assembly. Take special note of the structure of the type attribute's value... the namespace-qualified name of the class is specified, followed by a comma, followed by (at a bare minimum) the name of the assembly that contains the class. In the preceding example, the ExampleObject class is defined in the Examples namespace, and it has been compiled into the ExamplesLibrary assembly.

The name of the assembly that contains the type must be specified in the type attribute. Furthermore, it is recommended that you specify the fully qualified assembly name ^[2] in order to guarantee that the type that Spring.NET uses to instantiate your object (s) is indeed the one that you expect. Usually this is only an issue if you are using classes from (strongly named) assemblies that have been installed into the Global Assembly Cache (GAC).

If you have defined nested classes use the addition symbol, +, to reference the nested class. For example, if the class Examples.ExampleObject had a nested class Person the XML declaration would be

<object id="exampleObject" type="Examples.ExampleObject+Person, ExamplesLibrary"/>

If you are defining classes that have been compiled into assemblies that are available to your application (such as the bin directory in the case of ASP.NET applications) via the standard assembly probing mechanisms, then you can specify simply the name of the assembly (e.g. ExamplesLibrary.Data)... this way, when (or if) the assemblies used by your application are updated, you won't have to change the value of every <object/> definition's type attribute to reflect the new version number (if the version number has changed)... Spring.NET will automatically locate and use the newer versions of your assemblies (and their attendant classes) from that point forward.

When defining an object which is to be created using a static factory method, along with the type attribute which specifies the type containing the static factory method, another attribute named factory-method is needed to specify the name of the factory method itself. Spring.NET expects to be able to call this method (with an optional list of arguments as described later) and get back a live object, which from that point on is treated as if it had been created normally via a constructor. One use for such an object definition is to call static factories in legacy code.

Following is an example of an object definition which specifies that the object is to be created by calling a factory-method. Note that the definition does not specify the type (class) of the returned object, only the type containing the factory method. In this example, CreateInstance must be a static method.

<object id="exampleObject"
      type="Examples.ExampleObjectFactory, ExamplesLibrary"
      factory-method="CreateInstance"/>

The mechanism for supplying (optional) arguments to the factory method, or setting properties of the object instance after it has been returned from the factory, will be described shortly.

In a fashion similar to instantiation using a static factory method, instantiation using an instance factory method is where a non-static method of an existing object from the container is invoked to create the new object. To use this mechanism, the 'type' attribute must be left empty, and the 'factory-object' attribute must specify the name of an object in the current (or parent/ancestor) container that contains the instance method that is to be invoked to create the object. The name of the factory method itself should still be set via the 'factory-method' attribute.

<!-- the factory object, which contains an instance method called 'CreateInstance' -->
<object id="exampleFactory" type="...">
  <!-- inject any dependencies required by this object -->
</object>

<!-- the object that is to be created by the factory object -->
<object id="exampleObject"
      factory-method="CreateInstance"
      factory-object="exampleFactory"/>

Although the mechanisms for setting object properties are still to be discussed, one implication of this approach is that the factory object itself can be managed and configured via Dependency Injection, by the container.

	Note
	When the Spring documentation makes mention of a 'factory object', this will be a reference to an object that is configured in the Spring container that will create objects via an instance or static factory method. When the documentation mentions a IFactoryObject (notice the capitalization) this is a reference to a Spring-specific IFactoryObject .

The following examples shows the definition of simple generic types and how they can be created in Spring's XML based configuration file.

namespace GenericsPlay
{
    public class FilterableList<T>
    {
        private List<T> list;
        
        private String name;

        public List<T> Contents
        {
            get { return list; }
            set { list = value; }
        }

        public String Name
        {
            get { return name; }
            set { name = value; }
        }
        
        public List<T> ApplyFilter(string filterExpression)
        {
            /// should really apply filter to list ;)
            return new List<T>();
        }

    }
}

The XML configuration to create and configure this object is shown below

<object id="myFilteredIntList" type="GenericsPlay.FilterableList&lt;int>, GenericsPlay">
  <property name="Name" value="My Integer List"/>
</object>

There are a few items to note in terms how to specify a generic type. First, the left bracket that specifies the generic type, i.e. <, is replaced with the string &lt; due to XML escape syntax for the less than symbol. Yes, we all realize this is less than ideal from the readability point of view. Second, the generic type arguments can not be fully assembly qualified as the comma is used to separate generic type arguments. Alternative characters used to overcome the two quirks can be implemented in the future but so far, all proposals don't seem to help clarify the text. The suggested solution to improve readability is to use type aliases as shown below

<typeAliases>
 <alias name="GenericDictionary" type=" System.Collections.Generic.Dictionary&lt;,>" />
 <alias name="myDictionary" type="System.Collections.Generic.Dictionary&lt;int,string>" />
</typeAliases>

So that instead of something like this

<object id="myGenericObject" 
        type="GenericsPlay.ExampleGenericObject&lt;System.Collections.Generic.Dictionary&lt;int , string>>, GenericsPlay" />

It can be shortened to

<object id="myOtherGenericObject" 
        type="GenericsPlay.ExampleGenericObject&lt;GenericDictionary&lt;int , string>>, GenericsPlay" />

or even shorter

<object id="myOtherOtherGenericObject" 
        type="GenericsPlay.ExampleGenericObject&lt;MyIntStringDictionary>, GenericsPlay" />

Refer to Section 5.11, “Configuration of IApplicationContext” for additional information on using type aliases.

The following classes are used to demonstrate the ability to create instances of generic types that themselves are created via a static generic factory method.

public class TestGenericObject<T, U>
{
    public TestGenericObject()
    {
    }

    private IList<T> someGenericList = new List<T>();
    
    private IDictionary<string, U> someStringKeyedDictionary =
        new Dictionary<string, U>();

    public IList<T> SomeGenericList
    {
        get { return someGenericList; }
        set { someGenericList = value; }
    }

    public IDictionary<string, U> SomeStringKeyedDictionary
    {
        get { return someStringKeyedDictionary; }
        set { someStringKeyedDictionary = value; }
    }

}

The accompanying factory class is

public class TestGenericObjectFactory
{
    public static TestGenericObject<V, W> StaticCreateInstance<V, W>()
    {
        return new TestGenericObject<V, W>();
    }

    public TestGenericObject<V, W> CreateInstance<V, W>()
    {
        return new TestGenericObject<V, W>();
    }
}

The XML snippet to create an instance of TestGenericObject where V is a List of integers and W is an integer is shown below

<object id="myTestGenericObject"
        type="GenericsPlay.TestGenericObjectFactory, GenericsPlay"
        factory-method="StaticCreateInstance&lt;System.Collections.Generic.List&lt;int>,int>"
/>

The StaticCreateInstance method is responsible for instantiating the object that will be associated with the id 'myTestGenericObject'.

Using the class from the previous example the XML snippet to create an instance of a generic type via an instance factory method is shown below

<object id="exampleFactory" type="GenericsPlay.TestGenericObject&lt;int,string>, GenericsPlay"/>

<object id="anotherTestGenericObject"
        factory-object="exampleFactory" 
        factory-method="CreateInstance&lt;System.Collections.Generic.List&lt;int>,int>"/>

This creates an instance of TestGenericObject<List<int>,int>

Constructor-based DI is effected by invoking a constructor with a number of arguments, each representing a dependency. Additionally, calling a static factory method with specific arguments to construct the object, can be considered almost equivalent, and the rest of this text will consider arguments to a constructor and arguments to a static factory method similarly. Find below an example of a class that could only be dependency injected using constructor injection. Notice that there is nothing special about this class.

public class SimpleMovieLister
{
  // the SimpleMovieLister has a dependency on a MovieFinder
  private IMovieFinder movieFinder;

  // a constructor so that the Spring container can 'inject' a MovieFinder
  public MovieLister(IMovieFinder movieFinder)
  {
    this.movieFinder = movieFinder;
  }

  // business logic that actually 'uses' the injected IMovieFinder is omitted...

}

namespace X.Y
{
    public class Foo
    {
        public Foo(Bar bar, Baz baz)
        {
           // ...
        }
    }
}

<object name="Foo" type="X.Y.Foo, Example">
        <constructor-arg>
          <object type="X.Y.Bar, Example"/>
        </constructor-arg>
        <constructor-arg>
          <object type="X.Y.Baz, Example"/>
        </constructor-arg>
      </object>

using System;

namespace SimpleApp
{
  public class ExampleObject
  {
    private int years;              //No. of years to the calculate the Ultimate Answer

    private string ultimateAnswer;  //The Answer to Life, the Universe, and Everything

    public ExampleObject(int years, string ultimateAnswer)
    {
       this.years = years;
       this.ultimateAnswer = ultimateAnswer;
    }

}

<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
  <constructor-arg type="int" value="7500000"/>
  <constructor-arg type="string" value="42"/>
</object>

<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
  <constructor-arg index="0" value="7500000"/>
  <constructor-arg index="1" value="42"/>
</object>

<object name="exampleObject" type="SimpleApp.ExampleObject, SimpleApp">
  <constructor-arg name="years" value="7500000"/>
  <constructor-arg name="ultimateAnswer" value="42"/>
</object>

Setter-based DI is realized by calling setter methods on your objects after invoking a no-argument constructor or no-argument static factory method to instantiate your object.

Find below an example of a class that can only be dependency injected using pure setter injection.

public class MovieLister
{
  private IMovieFinder movieFinder;

  public IMovieFinder MovieFinder
  {
      set
      {
          movieFinder = value;
      }
  }

  // business logic that actually 'uses' the injected IMovieFinder is omitted...
}

The IObjectFactory supports both of these variants for injecting dependencies into objects it manages. (It in fact also supports injecting setter-based dependencies after some dependencies have already been supplied via the constructor approach.) The configuration for the dependencies comes in the form of the IObjectDefinition class, which is used together with TypeConverters to know how to convert properties from one format to another. However, most users of Spring.NET will not be dealing with these classes directly (that is programatically), but rather with an XML definition file which will be converted internally into instances of these classes, and used to load an entire Spring IoC container instance.

Object dependency resolution generally happens as follows:

The Spring container validates the configuration of each object as the container is created, including the validation that properties which are object references are actually referring to valid object. However, the object properties themselves are not set until the object is actually created. For those object that defined as singletons and set to be pre-instantiated (such as singleton object in an IApplicationContext), creation happens at the time that the container is created, but otherwise this is only when the object is requested. When an object actually has to be created, this will potentially cause a graph of other objects to be created, as its dependencies and its dependencies' dependencies (and so on) are created and assigned.

You can generally trust Spring.NET to do the right thing. It will detect configuration issues, such as references to non-existent object definitions and circular dependencies, at container load-time. It will actually set properties and resolve dependencies as late as possible, which is when the object is actually created. This means that a Spring container which has loaded correctly can later generate an exception when you request an object if there is a problem creating that object or one of its dependencies. This could happen if the object throws an exception as a result of a missing or invalid property, for example. This potentially delayed visibility of some configuration issues is why IApplicationContext by default pre-instantiates singleton objects. At the cost of some upfront time and memory to create these objects before they are actually needed, you find out about configuration issues when the IApplicationContext is created, not later. If you wish, you can still override this default behavior and set any of these singleton objects to lazy-load (not be preinstantiated)

If no circular dependencies are involved (see sidebar for a discussion of circular dependencies), when one or more collaborating objects are being injected into a dependent object, each collaborating object is totally configured prior to being passed (via one of the DI flavors) to the dependent object. This means that if object A has a dependency on object B, the Spring IoC container will totally configure object B prior to invoking the setter method on object A; you can read 'totally configure' to mean that the object will be instantiated (if not a pre-instantiated singleton), all of its dependencies will be set, and the relevant lifecycle methods (such as a configured init method or the IIntializingObject callback method) will all be invoked.

First, an example of using XML-based configuration metadata for setter-based DI. Find below a smallpart of a Spring XML configuration file specifying some object definitions.

<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary">

    <!-- setter injection using the ref attribute -->
    <property name="objectOne" ref="anotherExampleObject"/>    
    <property name="objectTwo" ref="yetAnotherObject"/>
    <property name="IntegerProperty" value="1"/>
</object>

<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>

[C#]
public class ExampleObject
{
  private AnotherObject objectOne;
  private YetAnotherObject objectTwo;
  private int i;
  
  public AnotherObject ObjectOne
  {
    set { this.objectOne = value; }
  }
  
  public YetAnotherObject ObjectTwo
  {
    set { this.objectTwo = value; }
  }
  
  public int IntegerProperty
  {
    set { this.i = value; }
  }  
}

As you can see, setters have been declared to match against the properties specified in the XML file. Find below an example of using constructor-based DI.

<object id="exampleObject" type="Examples.ExampleObject, ExamplesLibrary">
    <constructor-arg name="objectOne" ref="anotherExampleObject"/>
    <constructor-arg name="objectTwo" ref="yetAnotherObject"/>
    <constructor-arg name="IntegerProperty" value="1"/>
</object>

<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>

[Visual Basic.NET]
Public Class ExampleObject

    Private myObjectOne As AnotherObject
    Private myObjectTwo As YetAnotherObject
    Private i As Integer
    
    Public Sub New (
        anotherObject as AnotherObject,
        yetAnotherObject as YetAnotherObject,
        i as Integer)
        
        myObjectOne = anotherObject
        myObjectTwo = yetAnotherObject
        Me.i = i
    End Sub
End Class

As you can see, the constructor arguments specified in the object definition will be used to pass in as arguments to the constructor of the ExampleObject.

Now consider a variant of this where instead of using a constructor, Spring is told to call a static factory method to return an instance of the object

<object id="exampleObject" type="Examples.ExampleFactoryMethodObject, ExamplesLibrary"
     factory-method="CreateInstance">
    <constructor-arg name="objectOne" ref="anotherExampleObject"/>
    <constructor-arg name="objectTwo" ref="yetAnotherObject"/>
    <constructor-arg name="intProp" value="1"/>
</object>

<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>

[C#]
public class ExampleFactoryMethodObject
{
  private AnotherObject objectOne;
  private YetAnotherObject objectTwo;
  private int i;
  
  // a private constructor
  private ExampleFactoryMethodObject()
  {
  }

  public static ExampleFactoryMethodObject CreateInstance(AnotherObject objectOne,
                               YetAnotherObject objectTwo,
                               int intProp)
  {
    ExampleFactoryMethodObject fmo = new ExampleFactoryMethodObject();
    fmo.AnotherObject = objectOne;
    fmo.YetAnotherObject = objectTwo;
    fmo.IntegerProperty = intProp;
    return fmo;
  }

  // Property definitions

}

Note that arguments to the static factory method are supplied via constructor-arg elements, exactly the same as if a constructor had actually been used. These arguments are optional. Also, it is important to realize that the type of the class being returned by the factory method does not have to be of the same type as the class which contains the static factory method, although in this example it is. An instance (non-static) factory method, mentioned previously, would be used in an essentially identical fashion (aside from the use of the factory-object attribute instead of the type attribute), so will not be detailed here.

Note that Setter Injection and Constructor Injectionare not mutually exclusive. It is perfectly reasonable to use both for a single object definition, as can be seen in the following example:

<object id="exampleObject" type="Examples.MixedIocObject, ExamplesLibrary">
    <constructor-arg name="objectOne" ref="anotherExampleObject"/>
    <property name="objectTwo" ref="yetAnotherObject"/>
    <property name="IntegerProperty" value="1"/>
</object>

<object id="anotherExampleObject" type="Examples.AnotherObject, ExamplesLibrary"/>
<object id="yetAnotherObject" type="Examples.YetAnotherObject, ExamplesLibrary"/>

[C#]
public class MixedIocObject
{
  private AnotherObject objectOne;
  private YetAnotherObject objectTwo;
  private int i;
  
  public MixedIocObject (AnotherObject obj)
  {
    this.objectOne = obj;
  }
  
  public YetAnotherObject ObjectTwo
  {
    set { this.objectTwo = value; }
  }
  
  public int IntegerProperty
  {
    set { this.i = value; }
  }  
}

The <value/> element specifies a property or constructor argument as a human-readable string representation. As mentioned previously, TypeConverter instances are used to convert these string values from a System.String to the actual property or argument type. Custom TypeConverter implementations in the Spring.Objects.TypeConverters namespace are used to augment the functionality offered by the .NET BCL's default TypeConverter implementations.

In the following example, we use a SqlConnection from the System.Data.SqlClient namespace of the BCL. This class (like many other existing classes) can easily be used in a Spring.NET object factory, as it offers a convenient public property for configuration of its ConnectionString property.

<objects xmlns="http://www.springframework.net">
  <object id="myConnection" type="System.Data.SqlClient.SqlConnection">
      <!-- results in a call to the setter of the ConnectionString property -->
      <property
          name="ConnectionString"
          value="Integrated Security=SSPI;database=northwind;server=mySQLServer"/>
  </object>
</objects>

<object id="theTargetObject" type="..."> 
   . . .
</object>

<object id="theClientObject" type="...">
  <property name="targetName"> 
    <idref object="theTargetObject"/> 
  </property>
</object>

<object id="theTargetObject" type="..."> 
  . . .
</object>

<object id="theClientObject" type="...">
  <property name="targetName" value="theTargetObject"/> 
</object>

<property name="targetName">
  <idref local="theTargetObject"/> 
</property>

<property name="myProp">
  <value xml:space="preserve"> &#x000a;&#x000d;&#x0009;</value>
</property>

The ref element is the final element allowed inside a property definition element. It is used to set the value of the specified property to be a reference to another object managed by the container, a collaborator, so to speak. As you saw in the previous example to set collection properties, we used the SqlConnection instance from the initial example as a collaborator and specified it using a <ref object/> element. As mentioned in a previous section, the referred-to object is considered to be a dependency of the object who's property is being set, and will be initialized on demand as needed (if it is a singleton object it may have already been initialized by the container) before the property is set. All references are ultimately just a reference to another object, but there are 3 variations on how the id/name of the other object may be specified, which determines how scoping and validation is handled.

Specifying the target object by using the object attribute of the ref tag is the most general form, and will allow creating a reference to any object in the same IObjectFactory / IApplicationContext (whether or not in the same XML file), or parent IObjectFactory / IApplicationContext. The value of the object attribute may be the same as either the id attribute of the target object, or one of the values in the name attribute of the target object.

<ref object="someObject"/>

Specifying the target object by using the local attribute leverages the ability of the XML parser to validate XML id references within the same file. The value of the local attribute must be the same as the id attribute of the target object. The XML parser will issue an error if no matching element is found in the same file. As such, using the local variant is the best choice (in order to know about errors are early as possible) if the target object is in the same XML file.

<ref local="someObject"/>

Specifying the target object by using the parent attribute allows a reference to be created to an object that is in a parent IObjectFactory (orIApplicationContext) of the current IObjectFactory (or IApplicationContext). The value of the parent attribute may be the same as either the id attribute of the target object, or one of the values in the name attribute of the target object, and the target object must be in a parent IObjectFactory or IApplicationContext of the current one. The main use of this object reference variant is when there is a need to wrap an existing object in a parent context with some sort of proxy (which may have the same name as the parent), and needs the original object so it may wrap it.

<ref parent="someObject"/>

An object element inside the property element is used to define an object value inline, instead of referring to an object defined elsewhere in the container. The inline object definition does not need to have any id or name defined (indeed, if any are defined, they will be ignored).

<object id="outer" type="...">

  <!-- Instead of using a reference to target, just use an inner object --> 

  <property name="target"> 
    <object type="ExampleApp.Person, ExampleApp"> 
      <property name="name" value="Tony"/> 
      <property name="age" value="51"/> 
    </object>
  </property>
</object>

The list, set, name-values and dictionary elements allow properties and arguments of the type IList, ISet, NameValueCollection and IDictionary, respectively, to be defined and set.

<objects xmlns="http://www.springframework.net">
  <object id="moreComplexObject" type="Example.ComplexObject">
      <!--
      results in a call to the setter of the SomeList (System.Collections.IList) property
      -->
      <property name="SomeList">
          <list>
              <value>a list element followed by a reference</value>
              <ref object="myConnection"/>
          </list>
      </property>
      <!--
      results in a call to the setter of the SomeDictionary (System.Collections.IDictionary) property
      -->
      <property name="SomeDictionary">
          <dictionary>
              <entry key="a string => string entry" value="just some string"/>
              <entry key-ref="myKeyObject" value-ref="myConnection"/>
          </dictionary>
      </property>
      <!--
      results in a call to the setter of the SomeNameValue (System.Collections.NameValueCollection) property
      -->
      <property name="SomeNameValue">
          <name-values>
              <add key="HarryPotter" value="The magic property"/>
              <add key="JerrySeinfeld" value="The funny (to Americans) property"/>
          </name-values>
      </property>
      <!-- 
      results in a call to the setter of the SomeSet (Spring.Collections.ISet) property 
      -->
      <property name="someSet">
          <set>
              <value>just some string</value>
              <ref object="myConnection"/>
          </set>
      </property>
  </object>
</objects>

Many classes in the BCL expose only read-only properties for collection classes. When Spring.NET encounters a read-only collection, it will configure the collection by using the getter property to obtain a reference to the collection class and then proceed to add the additional elements to the existing collection. This results in an additive behavior for collection properties that are exposed in this manner.

Note that the value of a Dictionary entry, or a set value, can also again be any of the elements:

(object | ref | idref | expression | list | set | dictionary |
      name-values | value | null)

The shortcut forms for value and references are useful to reduce XML verbosity when setting collection properties. See Section 5.3.2.8, “Value and ref shortcut forms” for more information.

Spring supports setting values for classes that expose properties based on the generic collection interfaces IList<T> and IDictionary<TKey, TValue>. The type parameter for these collections is specified by using the XML attribute element-type for IList<T> and the XML attributes key-type and value-type for IDictionary<TKey, TValue>. The values of the collection are automaticaly converted from a string to the appropriate type. If you are using your own user-defined type as a generic type parameter you will likely need to register a custom type converter. Refer to Section 5.5, “Type conversion” for more information. The implementations of IList<T> and IDictionary<TKey, TValue> that is created are System.Collections.Generic.List and System.Collections.Generic.Dictionary.

The following class represents a lottery ticket and demonstrates how to set the values of a generic IList.

public class LotteryTicket { 

  List<int> list;

  DateTime date; 

  public List<int> Numbers { 
    set { list = value; }
    get { return list; } 
  }

  public DateTime Date { 
    get { return date; } 
    set { date = value; } 
  } 
}

The XML fragment that can be used to configure this class is shown below

<object id="MyLotteryTicket" type="GenericsPlay.Lottery.LotteryTicket, GenericsPlay">
  <property name="Numbers"> 
    <list element-type="int"> 
      <value>11</value>
      <value>21</value> 
      <value>23</value>
      <value>34</value> 
      <value>36</value>
      <value>38</value> 
    </list> 
  </property>
  <property name="Date" value="4/16/2006"/>
</object>

The following shows the definition of a more complex class that demonstrates the use of generics using the Spring.Expressions.IExpression interface as the generic type parameter for the IList element-type and the value-type for IDictionary. Spring.Expressions.IExpression has an associated type converter, Spring.Objects.TypeConverters.ExpressionConverter that is already pre-registered with Spring.

    public class GenericExpressionHolder
    {
        private System.Collections.Generic.IList<IExpression> expressionsList;

        private System.Collections.Generic.IDictionary<string,IExpression> expressionsDictionary;

        public System.Collections.Generic.IList<IExpression> ExpressionsList
        {
            set { this.expressionsList = value; }
        }

        public System.Collections.Generic.IDictionary<string, IExpression> ExpressionsDictionary
        {
            set { this.expressionsDictionary = value; }
        }

        public IExpression this[int index]
        {
            get
            {
                return this.expressionsList[index];
            }
        }

        public IExpression this[string key]
        {
            get { return this.expressionsDictionary[key]; }
        }
    }

An example XML configuration of this class is shown below

<object id="genericExpressionHolder"
    type="Spring.Objects.Factory.Xml.GenericExpressionHolder,
    Spring.Core.Tests">
    <property name="ExpressionsList">
        <list element-type="Spring.Expressions.IExpression, Spring.Core">
            <value>1 + 1</value>
            <value>date('1856-7-9').Month</value>
            <value>'Nikola Tesla'.ToUpper()</value>
            <value>DateTime.Today > date('1856-7-9')</value>
        </list>
    </property>
    <property name="ExpressionsDictionary">
        <dictionary key-type="string" value-type="Spring.Expressions.IExpression, Spring.Core">
            <entry key="zero">
                <value>1 + 1</value>
            </entry>
            <entry key="one">
                <value>date('1856-7-9').Month</value>
            </entry>
            <entry key="two">
                <value>'Nikola Tesla'.ToUpper()</value>
            </entry>
            <entry key="three">
                <value>DateTime.Today > date('1856-7-9')</value>
            </entry>
        </dictionary>
    </property>
</object>

The <null> element is used to handle null values. Spring.NET treats empty arguments for properties and constructor arguments as empty string instances. The following configuration demonstrates this behaviour...

<object type="Examples.ExampleObject, ExamplesLibrary"> 
  <property name="email"><value></value></property>

  <!-- equivalent, using value attribute as opposed to nested <value/> element... 
  <property name="email" value=""/> 
</object>

This results in the email property being set to the empty string value (""), in much the same way as can be seen in the following snippet of C# code...

exampleObject.Email = "";

The special <null/> element may be used to indicate a null value; to wit...

<object type="Examples.ExampleObject, ExamplesLibrary"> 
  <property name="email"><null/></property>
</object>

This results in the email property being set to null, again in much the same way as can be seen in the following snippet of C# code...

exampleObject.Email = null;

An indexer lets you set and get values from a collection using a familiar bracket [] notation. Spring's XML configuration supports the setting of indexer properties. Overloaded indexers as well as multiparameter indexers are also supported. The property expression parser described in Chapter 11, Expression Evaluation is used to perform the type conversion of the indexer name argument from a string in the XML file to a matching target type. As an example consider the following class

public class Person
{
    private IList favoriteNames = new ArrayList();

    private IDictionary properties = new Hashtable();

    public Person()
    {
        favoriteNames.Add("p1");
        favoriteNames.Add("p2");
    }

    public string this[int index]
    {
        get { return (string) favoriteNames[index]; }
        set { favoriteNames[index] = value; }
    }

    public string this[string keyName]
    {
        get { return (string) properties[keyName]; }
        set { properties.Add(keyName, value); }
    }
}

The XML configuration snippet to populate this object with data is shown below

<object id="person" type="Test.Objects.Person, Test.Objects">
    <property name="[0]" value="Master Shake"/>
    <property name="['one']" value="uno"/>
</object>

Note

The use of the property expression parser in Release 1.0.2 changed how you configure indexer properties. The following section describes this usage. The older style configuration uses the following syntax <object id="objectWithIndexer" type="Spring.Objects.TestObject, Spring.Core.Tests"> <property name="Item[0]" value="my string value"/> </object> You can also change the name used to identify the indexer by adorning your indexer method declaration with the attribute [IndexerName("MyItemName")]. You would then use the string MyItemName[0] to configure the first element of that indexer. There are some limitations to be aware in the older indexer configuration. The indexer can only be of a single parameter that is convertible from a string to the indexer parameter type. Also, multiple indexers are not supported. You can get around that last limitation currently if you use the IndexerName attribute.

There are also some shortcut forms that are less verbose than using the full value and ref elements. The property, constructor-arg, and entry elements all support a value attribute which may be used instead of embedding a full value element. Therefore, the following:

<property name="myProperty">
      <value>hello</value>
</property>

<constructor-arg> 
  <value>hello</value>
</constructor-arg> 

<entry key="myKey">
  <value>hello</value>
</entry>

are equivalent to:

<property name="myProperty" value="hello"/>

<constructor-arg value="hello"/> 

<entry key="myKey" value="hello"/>

In general, when typing definitions by hand, you will probably prefer to use the less verbose shortcut form.

The property and constructor-arg elements support a similar shortcut ref attribute which may be used instead of a full nested ref element. Therefore, the following...

<property name="myProperty"> 
  <ref object="anotherObject"/>
</property>

<constructor-arg index="0"> 
  <ref object="anotherObject"/> 
</constructor-arg>

is equivalent to...

<property name="myProperty" ref="anotherObject"/>

<constructor-arg index="0" ref="anotherObject"/>

	Note
	The shortcut form is equivalent to a <ref object="xxx"> element; there is no shortcut for either the <ref local="xxx"> or <ref parent="xxx"> elements. For a local or parent ref, you must still use the long form.

Finally, the entry element allows a shortcut form the specify the key and/or value of a dictionary, in the form of key/key-ref and value/value-ref attributes. Therefore, the following

<entry> 
  <key>
     <ref object="MyKeyObject"/>
  </key> 
  <ref object="MyValueObject"/> 
</entry>

Is equivalent to:

<entry key-ref="MyKeyObject" value-ref="MyValueObject"/>

As mentioned previously, the equivalence is to <ref object="xxx"> and not the local or parent forms of object references.

Note that compound or nested property names are perfectly legal when setting object properties. Property names are interpreted using the Spring Expression Language (SpEL) and therefore can leverage its many features to set property names. For example, in this object definition a simple nested property name is configured

<object id="foo" type="Spring.Foo, Spring.Foo"> 
  <property name="bar.baz.name" value="Bingo"/> 
</object>

As an example of some alternative ways to declare the property name, you can use SpEL's support for indexers to configure a Dictionary key value pair as an alternative to the nested <dictionary> element. More importantly, you can use the 'expression' element to refer to a Spring expression as the value of the property. Simple examples of this are shown below

<property name=“minValue” expression=“int.MinValue” />

<property name=“weekFromToday” expression="DateTime.Today + 7"/>

Using SpEL's support for method evaluation, you can easily call static method on various helper classes in your XML configuraiton.

Rather than having to specifically declare in your code that you are adding a method to be invoked on an event, using the <listener> element you can register a plain object's methods with the corresponding event declaratively in your application configuration.

Using the listener element you can:

The same event registration in the example above can be achieved using configuration using the <listener> element.

<object id="eventListener1" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
   <!-- wired up to an event exposed on an instance -->
   <listener event="Click" method="HandleEvent">
      <ref object="source"/>
   </listener>
</object>

<object id="eventListener2" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
   <!-- wired up to an event exposed on an instance -->
   <listener event="Click" method="HandleEvent">
      <ref object="source"/>
   </listener>
</object>

In this case the two different objects will have their HandleEvent method invoked, as indicated explicitly using the method attribute, when a Click event, as specified by the event attribute, is triggered on the object referred to by the ref element.

Regular expressions can be employed to wire up more than one handler method to an object that contains one or more events.

<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
   <listener method="Handle.+">
      <ref object="source"/>
   </listener>
</object>

Here all the eventListener's handler methods that begin with 'Handle', and that have the corresponding two parameters of a System.Object and a System.EventArgs, will be registered against all events exposed by the source object.

You can also use the name of the event in regular expression to filter your handler methods based on the type of event triggered.

<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
   <!-- For the Click event, the HandleClick handler method will be invoked. -->
   <listener method="Handle${event}">
      <ref object="source"/>
   </listener>
</object>

Finally, you can register an object's handler methods against a selection of events, filtering based on their name using a regular expression.

<object id="eventListener" type="SpringdotNETEventsExample.TestEventHandler, SpringdotNETEventsExample">
   <listener method="HandleEvent" event="Cl.+">
      <ref object="source"/>
   </listener>
</object>

In this example the eventListener's HandleEvent handler method will be invoked for any event that begins with 'Cl'.

• Autowiring can significantly reduce the volume of configuration required. However, mechanisms such as the use of a object template (discussed elsewhere in this chapter) are also valuable in this regard.

• Autowiring can cause configuration to keep itself up to date as your objects evolve. For example, if you need to add an additional dependency to a class, that dependency can be satisfied automatically without the need to modify configuration. Thus there may be a strong case for autowiring during development, without ruling out the option of switching to explicit wiring when the code base becomes more stable.

• Autowiring is more magical than explicit wiring. Although, as noted in the above table, Spring is careful to avoid guessing in case of ambiguity which might have unexpected results, the relationships between your Spring-managed objects are no longer documented explicitly.

• Wiring information may not be available to tools that may generate documentation from a Spring container.

Lookup method injection refers to the ability of the container to override abstract or concrete methods on container managed objects, to return the result of looking up another named object in the container. The lookup will typically be of a prototype object as in the scenario described above. The Spring framework implements this method injection by a dynamically generating a subclass overriding the method using the classes in the System.Reflection.Emit namespace. You can read more about the motivation for Method Injection in this blog entry.

So if you look at the code from the previous code snipped (the CommandManager class), the Spring container is going to dynamically override the implementation of the CreateCommand() method. Your CommandManager class is not going to have any Spring dependencies, as can be seen in this reworked example below:

using System.Collections;

namespace Fiona.Apple
{
    public abstract class CommandManager
    {

        public object Process(IDictionary commandState)
        {
            Command command = CreateCommand();
            command.State = commandState;
            return command.Execute();
        }

        // okay... but where is the implementation of this method?
        protected abstract Command CreateCommand();
    }
}

In the client class containing the method to be injected (the CommandManager in this case) the method definition must observe the following form:

<public|protected> [abstract] <return-type> TheMethodName(no-arguments);

If the method is abstract, the dynamically-generated subclass will implement the method. Otherwise, the dynamically-generated subclass will override the concrete method defined in the original class. Let's look at an example:

<!-- a stateful object deployed as a prototype (non-singleton) -->
<object id="command" class="Fiona.Apple.AsyncCommand, Fiona" singleton="false">
  <!-- inject dependencies here as required -->
</object>

<!-- commandProcessor uses a statefulCommandHelpder -->
<object id="commandManager" type="Fiona.Apple.CommandManager, Fiona">
  <lookup-method name="CreateCommand" object="command"/>
</object>

The object identified as commandManager will call its own method CreateCommand whenever it needs a new instance of the command object. It is important to note that the person deploying the objects must be careful to deploy the command object as prototype (if that is actually what is needed). If it is deployed as a singleton the same instance of singleShotHelper will be returned each time!

Note that lookup method injection can be combined with Constructor Injection (supplying optional constructor arguments to the object being constructed), and also with Setter Injection (settings properties on the object being constructed).

A less commonly useful form of method injection than Lookup Method Injection is the ability to replace arbitrary methods in a managed object with another method implementation. Users may safely skip the rest of this section (which describes this somewhat advanced feature), until this functionality is actually needed.

In an XmlObjectFactory, the replaced-method element may be used to replace an existing method implementation with another. Consider the following class, with a method ComputeValue, which we want to override:

public class MyValueCalculator {

  public virtual string ComputeValue(string input) {
    // ... some real code
  }

  // ... some other methods
}

A class implementing the Spring.Objects.Factory.Support.IMethodReplacer interface is needed to provide the new (injected) method definition.

/// <summary>
/// Meant to be used to override the existing ComputeValue(string)
/// implementation in MyValueCalculator.
/// </summary>
public class ReplacementComputeValue : IMethodReplacer 
{
	public object Implement(object target, MethodInfo method, object[] arguments)
	{
		// get the input value, work with it, and return a computed result...
		string value = (string) arguments[0];
		// compute...
		return result;
	}
}

The object definition to deploy the original class and specify the method override would look like this:

<object id="myValueCalculator" type="Examples.MyValueCalculator, ExampleAssembly">
  <!-- arbitrary method replacement -->
  <replaced-method name="ComputeValue" replacer="replacementComputeValue">
    <arg-type match="String"/>
  </replaced-method>
</object>

<object id="replacementComputeValue" type="Examples.ReplacementComputeValue, ExampleAssembly"/>

One or more contained arg-type elements within the replaced-method element may be used to indicate the method signature of the method being overridden. Note that the signature for the arguments is actually only needed in the case that the method is actually overloaded and there are multiple variants within the class. For convenience, the type string for an argument may be a substring of the fully qualified type name. For example, all the following would match System.String.

    System.String
    String
    Str

Since the number of arguments is often enough to distinguish between each possible choice, this shortcut can save a lot of typing, by just using the shortest string which will match an argument.

The PropertyRetrievingFactoryObject is an IFactoryObject that addresses the scenario of setting one of the properties and / or constructor arguments of an object to the value of a property exposed on another object or class. One can use it to get the value of any public property exposed on either an instance or a class (in the case of a property exposed on a class, the property must obviously be static).

In the case of a property exposed on an instance, the target object that a PropertyRetrievingFactoryObject will evaluate can be either an object instance specified directly inline or a reference to another arbitrary object. In the case of a static property exposed on a class, the target object will be the class (the .NET System.Type) exposing the property.

The result of evaluating the property lookup may then be used in another object definition as a property value or constructor argument. Note that nested properties are supported for both instance and class property lookups. The IFactoryObject is discussed more generally in Section 5.9.3, “Customizing instantiation logic using IFactoryObjects”.

Here's an example where a property path is used against another object instance. In this case, an inner object definition is used and the property path is nested, i.e. spouse.age.

<object name="person" type="Spring.Objects.TestObject, Spring.Core.Tests">
  <property name="age" value="20"/>
  <property name="spouse">
    <object type="Spring.Objects.TestObject, Spring.Core.Tests">                      
      <property name="age" value="21"/>
    </object>
  </property>          
</object>
        
// will result in 21, which is the value of property 'spouse.age' of object 'person'        
<object name="theAge" type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
  <property name="TargetObject" ref="person"/>
  <property name="TargetProperty" value="spouse.age"/>
</object>

An example of using a PropertyRetrievingFactoryObject to evaluate a static property is shown below.

<object id="cultureAware" 
        type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
  <property name="culture" ref="cultureFactory"/>
</object>

<object id="cultureFactory" 
        type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
  <property name="StaticProperty">
      <value>System.Globalization.CultureInfo.CurrentUICulture, Mscorlib</value>
  </property>
</object>

Similarly, an example showing the use of an instance property is shown below.

<object id="instancePropertyCultureAware" 
        type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
  <property name="Culture" ref="instancePropertyCultureFactory"/>
</object>

<object id="instancePropertyCultureFactory" 
        type="Spring.Objects.Factory.Config.PropertyRetrievingFactoryObject, Spring.Core">
  <property name="TargetObject" ref="instancePropertyCultureAwareSource"/>
  <property name="TargetProperty" value="MyDefaultCulture"/>
</object>

<object id="instancePropertyCultureAwareSource" 
        type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests"/>
    

The FieldRetrievingFactoryObject class addresses much the same area of concern as the PropertyRetrievingFactoryObject described in the previous section. However, as its name might suggest, the FieldRetrievingFactoryObject class is concerned with looking up the value of a public field exposed on either an instance or a class (and similarly, in the case of a field exposed on a class, the field must obviously be static).

The following example demonstrates using a FieldRetrievingFactoryObject to look up the value of a (public, static) field exposed on a class

<object id="withTypesField" 
        type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
  <property name="Types" ref="emptyTypesFactory"/>
</object>

<object id="emptyTypesFactory" 
        type="Spring.Objects.Factory.Config.FieldRetrievingFactoryObject, Spring.Core">
  <property name="TargetType" value="System.Type, Mscorlib"/>
    <property name="TargetField" value="EmPTytypeS"/>
</object>
      

The example in the next section demonstrates the look up of a (public) field exposed on an object instance.

<object id="instanceCultureAware" 
        type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests">
  <property name="Culture" ref="instanceCultureFactory"/>
</object>

<object id="instanceCultureFactory"
  type="Spring.Objects.Factory.Config.FieldRetrievingFactoryObject, Spring.Core">
  <property name="TargetObject" ref="instanceCultureAwareSource"/>
  <property name="TargetField" value="Default"/>
</object>

<object id="instanceCultureAwareSource" 
         type="Spring.Objects.Factory.Xml.XmlObjectFactoryTests+MyTestObject, Spring.Core.Tests"/>
    

The MethodInvokingFactoryObject rounds out the trio of classes that permit the setting of properties and constructor arguments using the members of other objects and classes. Whereas the PropertyRetrievingFactoryObject and FieldRetrievingFactoryObject classes dealt with simply looking up and returning the value of property or field on an object or class, the MethodInvokingFactoryObject allows one to set a constructor or property to the return value of an arbitrary method invocation,

The MethodInvokingFactoryObject class handles both the case of invoking an (instance) method on another object in the container, and the case of a static method call on an arbitrary class. Additionally, it is sometimes necessary to invoke a method just to perform some sort of initialization.... while the mechanisms for handling object initialization have yet to be introduced (see Section 5.6.1.1, “IInitializingObject / init-method”), these mechanisms do not permit any arguments to be passed to any initialization method, and are confined to invoking an initialization method on the object that has just been instantiated by the container. The MethodInvokingFactoryObject allows one to invoke pretty much any method on any object (or class in the case of a static method).

The following example (in an XML based IObjectFactory definition) uses the MethodInvokingFactoryObject class to force a call to a static factory method prior to the instantiation of the object...

<object id="force-init"
  type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
  <property name="StaticMethod">
    <value>ExampleNamespace.ExampleInitializerClass.Initialize</value>
  </property>
</object>
<object id="myService" depends-on="force-init"/>

Note that the definition for the myService object has used the depends-on attribute to refer to the force-init object, which will force the initialization of the force-init object first (and thus the calling of its configured StaticMethod static initializer method, when myService is first initialized. Please note that in order to effect this initialization, the MethodInvokingFactoryObject object must be operating in singleton mode (the default.. see the next paragraph).

Note that since this class is expected to be used primarily for accessing factory methods, this factory defaults to operating in singleton mode. As such, as soon as all of the properties for a MethodInvokingFactoryObject object have been set, and if the MethodInvokingFactoryObject object is still in singleton mode, the method will be invoked immediately and the return value cached for later access. The first request by the container for the factory to produce an object will cause the factory to return the cached return value for the current request (and all subsequent requests). The IsSingleton property may be set to false, to cause this factory to invoke the target method each time it is asked for an object (in this case there is obviously no caching of the return value).

A static target method may be specified by setting the targetMethod property to a string representing the static method name, with TargetType specifying the Type that the static method is defined on. Alternatively, a target instance method may be specified, by setting the TargetObject property to the name of another Spring.NET managed object definition (the target object), and the TargetMethod property to the name of the method to call on that target object.

Arguments for the method invocation may be specified in two ways (or even a mixture of both)... the first involves setting the Arguments property to the list of arguments for the method that is to be invoked. Note that the ordering of these arguments is significant... the order of the values passed to the Arguments property must be the same as the order of the arguments defined on the method signature, including the argument Type. This is shown in the example below

<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
  <property name="TargetType" value="Whatever.MyClassFactory, MyAssembly"/>
  <property name="TargetMethod" value="GetInstance"/>
  
  <!-- the ordering of arguments is significant -->
  <property name="Arguments">
    <list>
      <value>1st</value>
      <value>2nd</value>
      <value>and 3rd arguments</value>
      <!-- automatic Type-conversion will be performed prior to invoking the method -->
    </list>
  </property>
</object>

The second way involves passing an arguments dictionary to the NamedArguments property... this dictionary maps argument names (Strings) to argument values (any object). The argument names are not case-sensitive, and order is (obviously) not significant (since dictionaries by definition do not have an order). This is shown in the example below

<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
  <property name="TargetObject">
    <object type="Whatever.MyClassFactory, MyAssembly"/>
  </property>
  <property name="TargetMethod" value="Execute"/>
  
  <!-- the ordering of named arguments is not significant -->
  <property name="NamedArguments">
    <dictionary>
      <entry key="argumentName"><value>1st</value></entry>
      <entry key="finalArgumentName"><value>and 3rd arguments</value></entry>
      <entry key="anotherArgumentName"><value>2nd</value></entry>
    </dictionary>
  </property>
</object>

The following example shows how use MethodInvokingFactoryObject to call an instance method.

<object id="myMethodObject" type="Whatever.MyClassFactory, MyAssembly" />

<object id="myObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
  <property name="TargetObject" ref="myMethodObject"/>
  <property name="TargetMethod" value="Execute"/>
</object>

The above example could also have been written using an anonymous inner object definition... if the object on which the method is to be invoked is not going to be used outside of the factory object definition, then this is the preferred idiom because it limits the scope of the object on which the method is to be invoked to the surrounding factory object.

Finally, if you want to use MethodInvokingFactoryObject in conjunction with a method that has a variable length argument list, then please note that the variable arguments need to be passed (and configured) as a list. Let us consider the following method definition that uses the params keyword (in C#), and its attendant (XML) configuration...

[C#]
public class MyClassFactory
{
    public object CreateObject(Type objectType, params string[] arguments)
    {
        return ... // implementation elided for clarity...
    }
}

<object id="myMethodObject" type="Whatever.MyClassFactory, MyAssembly" />

<object id="paramsMethodObject" type="Spring.Objects.Factory.Config.MethodInvokingFactoryObject, Spring.Core">
  <property name="TargetObject" ref="myMethodObject"/>
  <property name="TargetMethod" value="CreateObject"/>
  <property name="Arguments">
    <list>
      <value>System.String</value>
      <!-- here is the 'params string[] arguments' -->
      <list>
        <value>1st</value>
        <value>2nd</value>
      </list>
    </list>
</object>

The LogFactoryObject is useful when you would like to share a Common.Logging log object across a number of classes instead of creating a logging instance per class or class hierarchy. Information on the Common.Logging project can be found here. In the example shown below the same logging instance, with a logging category name of "DAOLogger", is used in both the SimpleAccountDao and SimpleProductDao data access objects.

<objects xmlns="http://www.springframework.net" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://www.springframework.net
         http://www.springframework.net/xsd/spring-objects.xsd" >

    <object name="daoLogger" type="Spring.Objects.Factory.Config.LogFactoryObject, Spring.Core">
      <property name="logName" value="DAOLogger"/>
    </object>
        
    <object name="productDao" type="PropPlayApp.SimpleProductDao, PropPlayApp ">
      <property name="maxResults" value="100"/>
      <property name="dbConnection" ref="myConnection"/>
      <property name="log" ref="daoLogger"/>
    </object>

    <object name="accountDao" type="PropPlayApp.SimpleAccountDao, PropPlayApp ">
      <property name="maxResults" value="100"/>
      <property name="dbConnection" ref="myConnection"/>
      <property name="log" ref="daoLogger"/>
    </object>
    
    <object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data"> 
      <property name="connectionstring" value="dsn=MyDSN;uid=sa;pwd=myPassword;"/> 
    </object> 
    
</objects>

This section shows in detail how to define a custom type converter that does not use the .NET TypeConverter attribute. The type converter class is standalone and inherits from the TypeConverter class. It uses the legacy factory post-processor approach.

Consider a user class ExoticType, and another class DependsOnExoticType which needs ExoticType set as a property:

public class ExoticType
{
    private string name;
        
    public ExoticType(string name)
    {
        this.name = name;
    }

    public string Name
    {
        get { return this.name; }
    }
}

and

public class DependsOnExoticType
{
    public DependsOnExoticType() {}
    
    private ExoticType exoticType;
        
    public ExoticType ExoticType
    {
        get { return this.exoticType; }
        set { this.exoticType = value; }
    }
    
    public override string ToString()
    {
        return exoticType.Name;
    }
}

When things are properly set up, we want to be able to assign the type property as a string, which a TypeConverter will convert into a real ExoticType object behind the scenes:

<object name="sample" type="SimpleApp.DependsOnExoticType, SimpleApp">
  <property name="exoticType" value="aNameForExoticType"/>
</object>

The TypeConverter looks like this:

public class ExoticTypeConverter : TypeConverter
{
	public ExoticTypeConverter()
	{
	}

	public override bool CanConvertFrom (
		ITypeDescriptorContext context, 
		Type sourceType) 
	{
		if (sourceType == typeof (string)) 
		{
			return true;
		}
		return base.CanConvertFrom (context, sourceType);
	}

	public override object ConvertFrom (
		ITypeDescriptorContext context, 
		CultureInfo culture, object value) 
	{
		string s = value as string;
		if (s != null) 
		{          
			return new ExoticType(s.ToUpper());
		}
		return base.ConvertFrom (context, culture, value);
	}
}

Finally, we use the CustomConverterConfigurer to register the new TypeConverter with the IApplicationContext, which will then be able to use it as needed:

<object id="customConverterConfigurer" 
	type="Spring.Objects.Factory.Config.CustomConverterConfigurer, Spring.Core">
  <property name="CustomConverters">
    <dictionary>
      <entry key="SimpleApp.ExoticType">
        <object type="SimpleApp.ExoticTypeConverter"/>
      </entry>
    </dictionary>
  </property>
</object>

The Spring.Objects.Factory.IInitializingObject interface gives you the ability to perform initialization work after all the necessary properties on an object are set by the container. The IInitializingObject interface specifies exactly one method:

	Note
	Generally, the use of the IInitializingObject can be avoided. The Spring.Core library provides support for a generic init-method, given to the object definition in the object configuration store (be it XML, or a database, etc).

<object id="exampleInitObject" type="Examples.ExampleObject" init-method="init"/>
[C#]
public class ExampleObject
{
    public void Init()
    {
        // do some initialization work
    }
}

Is exactly the same as...

<object id="exampleInitObject" type="Examples.AnotherExampleObject"/>
[C#]
public class AnotherExampleObject : IInitializingObject
{
    public void AfterPropertiesSet()
    {
        // do some initialization work
    }
}

but does not couple the code to Spring.NET.

Note

When deploying an object in prototype mode, the lifecycle of the object changes slightly. By definition, Spring.NET cannot manage the complete lifecycle of a non-singleton / prototype object, since after it is created, it is given to the client and the container no longer keeps a reference to the object. You can think of Spring.NET's role when talking about a non-singleton ( prototype ) object as a replacement for the new operator. Any lifecycle aspects past that point have to be handled by the client.

The System.IDisposable interface provides you with the ability to get a callback when an IObjectFactory is destroyed. The IDisposable interface specifies exactly one method:

	Note
	Note: If you choose you can avoid having your class implement IDisposable since the Spring.Core library provides support for a generic destroy-method, given to the object definition in the object configuration store (be it XML, or a database, etc).

<object id="exampleInitObject" type="Examples.ExampleObject" destroy-method="cleanup"/>
[C#]
public class ExampleObject
{
    public void cleanup()
    {
        // do some destruction work (such as closing any open connection (s))
    }
}

is exactly the same as:

<object id="exampleInitObject" type="Examples.AnotherExampleObject"/>
[C#]
public class AnotherExampleObject : IDisposable
{
    public void Dispose()
    {
        // do some destruction work
    }
}

A class which implements the Spring.Objects.Factory.IObjectFactoryAware interface is provided with a reference to the IObjectFactory that created it. The interface specifies one (write-only) property:

This allows objects to manipulate the IObjectFactory that created them Programatically, through the IObjectFactory interface, or by casting the reference to a known subclass of this which exposes additional functionality. Primarily this would consist of programmatic retrieval of other objects. While there are cases when this capability is useful, it should generally be avoided, since it couples the code to Spring.NET, and does not follow the Inversion of Control style, where collaborators are provided to objects as properties.

The Spring.Objects.Factory.IObjectNameAware interface gives you the ability to let the container set the name of the object definition on the object instance itself. In those cases where your object needs to know what its name is, implement this interface.

This first example is hardly compelling, but serves to illustrate basic usage. All we are going to do is code a custom IObjectPostProcessor implementation that simply invokes the ToString() method of each object as it is created by the container and prints the resulting string to the system console. Yes, it is not hugely useful, but serves to get the basic concepts across before we move into the second example which is actually useful. The basis of the example is the MovieFinder quickstart that is included with the Spring.NET distribution.

Find below the custom IObjectPostProcessor implementation class definition

using System;
using Spring.Objects.Factory.Config;

namespace Spring.IocQuickStart.MovieFinder
{
    public class TracingObjectPostProcessor : IObjectPostProcessor
    {
        public object PostProcessBeforeInitialization(object instance, string name)
        {
            return instance;
        }

        public object PostProcessAfterInitialization(object instance, string name)
        {
            Console.WriteLine("Object '" + name + "' created : " + instance.ToString());
            return instance;
        }
    }
}

And the following configuration

<?xml version="1.0" encoding="utf-8" ?>
<objects xmlns="http://www.springframework.net" >
  <description>An example that demonstrates simple IoC features.</description>

  <object id="MyMovieLister" 
          type="Spring.IocQuickStart.MovieFinder.MovieLister, Spring.IocQuickStart.MovieFinder">
    <property name="movieFinder" ref="MyMovieFinder"/>
  </object>

  <object id="MyMovieFinder" 
          type="Spring.IocQuickStart.MovieFinder.SimpleMovieFinder, Spring.IocQuickStart.MovieFinder"/>

  <!-- when the above objects are instantiated, this custom IObjectPostProcessor implementation 
       will output the fact to the system console -->
  <object type="Spring.IocQuickStart.MovieFinder.TracingObjectPostProcessor, Spring.IocQuickStart.MovieFinder"/>
</objects>

Notice how the TracingObjectPostProcessor is simply defined; it doesn't even have a name, and because it is a object it can be dependency injected just like any other object.

Find below a small driver script to exercise the above code and configuration;

IApplicationContext ctx =
        new XmlApplicationContext(
            "assembly://Spring.IocQuickStart.MovieFinder/Spring.IocQuickStart.MovieFinder/AppContext.xml");

MovieLister lister = (MovieLister) ctx.GetObject("MyMovieLister");
Movie[] movies = lister.MoviesDirectedBy("Roberto Benigni");
LOG.Debug("Searching for movie...");
foreach (Movie movie in movies)
{
  LOG.Debug(string.Format("Movie Title = '{0}', Director = '{1}'.", movie.Title, movie.Director));
}
LOG.Debug("MovieApp Done.");

The output of executing the above program will be:

INFO  - Object 'Spring.IocQuickStart.MovieFinder.TracingObjectPostProcessor' is not eligible for being processed by all IObjectPostProcessors 
       (for example: not eligible for auto-proxying).
Object 'MyMovieFinder' created : Spring.IocQuickStart.MovieFinder.SimpleMovieFinder
Object 'MyMovieLister' created : Spring.IocQuickStart.MovieFinder.MovieLister
DEBUG - Searching for movie...
DEBUG - Movie Title = 'La vita e bella', Director = 'Roberto Benigni'.
DEBUG - MovieApp Done.

Using callback interfaces or annotations in conjunction with a custom IObjectPostProcessor implementation is a common means of extending the Spring IoC container. The [Required] attribute in the Spring.Objects.Factory.Attributes namespace can be used to mark a property as being 'required-to-be-set' (i.e. an setter property with this attribute applied must be configured to be dependency injected with a value), else an ObjectInitializationException will be thrown by the container at runtime.

The best way to illustrate the usage of this attribute is with an example.

public class MovieLister
{
  // the MovieLister has a dependency on the MovieFinder
  private IMovieFinder _movieFinder;

  // a setter property so that the Spring container can 'inject' a MovieFinder
  [Required]
  public IMovieFinder MovieFinder
  {
    set { _movieFinder = value; }  
  }

  // business logic that actually 'uses' the injected MovieFinder is omitted...

}

Hopefully the above class definition reads easy on the eye. Any and all IObjectDefinitions for the MovieLister class must be provided with a value.

Let's look at an example of some XML configuraiton that will not pass validation.

<object id="MyMovieLister" 
          type="Spring.IocQuickStart.MovieFinder.MovieLister, Spring.IocQuickStart.MovieFinder">
      <!-- whoops, no MovieFinder is set (and this property is [Required]) -->
  </object>

At runtime the following message will be generated by the Spring container

Error creating context 'spring.root': Property 'MovieFinder' required for object 'MyMovieLister'

There is one last little piece of Spring configuration that is required to actually 'switch on' this behavior. Simply annotating the 'setter' properties of your classes is not enough to get this behavior. You need to enable a component that is aware of the [Required] attribute and that can process it appropriately.

This component is the RequiredAttributeObjectPostProcessor class. This is a special IObjectPostProcessor implementation that is [Required]-aware and actually provides the 'blow up if this required property has not been set' logic. It is very easy to configure; simply drop the following object definition into your Spring XML configuration.

<object type="Spring.Objects.Factory.Attributes.RequiredAttributeObjectPostProcessor, Spring.Core"/>

Finally, one can configure an instance of the RequiredAttributeObjectPostProcessor class to look for another Attribute type. This is great if you already have your own [Required]-style attribute. Simply plug it into the definition of a RequiredAttributeObjectPostProcessor and you are good to go. By way of an example, let's suppose you (or your organization / team) have defined an attribute called [Mandatory]. You can make a RequiredAttributeObjectPostProcessor instance [Mandatory]-aware like so:

<object type="Spring.Objects.Factory.Attributes.RequiredAttributeObjectPostProcessor, Spring.Core">
  <property name="RequiredAttributeType" value="MyApp.Attributes.MandatoryAttribute, MyApp"/>
</object>

The PropertyPlaceholderConfigurer is an excellent solution when you want to externalize a few properties from a file containing object definitions. This is useful to allow the person deploying an application to customize environment specific properties (for example database configuration strings, usernames, and passwords), without the complexity or risk of modifying the main XML definition file or files for the container.

Variable substitution is performed on simple property values, lists, dictionaries, sets, constructor values, object type name, and object names in runtime object references. Furthermore, placeholder values can also cross-reference other placeholders.

Note that IApplicationContexts are able to automatically recognize and apply objects deployed in them that implement the IObjectFactoryPostProcessor interface. This means that as described here, applying a PropertyPlaceholderConfigurer is much more convenient when using an IApplicationContext. For this reason, it is recommended that users wishing to use this or other object factory postprocessors use an IApplicationContext instead of an IObjectFactory.

In the example below a data access object needs to be configured with a database connection and also a value for the maximum number of results to return in a query. Instead of hard coding the values into the main Spring.NET configuration file we use place holders, in the NAnt style of ${variableName}, and obtain their values from NameValueSections in the standard .NET application configuration file. The Spring.NET configuration file looks like:

<configuration>

  <configSections>
    <sectionGroup name="spring">
      <section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
    </sectionGroup>
    <section name="DaoConfiguration" type="System.Configuration.NameValueSectionHandler"/>
    <section name="DatabaseConfiguration" type="System.Configuration.NameValueSectionHandler"/>
  </configSections>

  <DaoConfiguration>
    <add key="maxResults" value="1000"/>
  </DaoConfiguration>
  
  <DatabaseConfiguration>
    <add key="connection.string" value="dsn=MyDSN;uid=sa;pwd=myPassword;"/>
  </DatabaseConfiguration>
  
  <spring>
    <context>
      <resource uri="assembly://DaoApp/DaoApp/objects.xml"/>
    </context>
  </spring>

</configuration>

Notice the presence of two NameValueSections in the configuration file. These name value pairs will be referred to in the Spring.NET configuration file. In this example we are using an embedded assembly resource for the location of the Spring.NET configuration file so as to reduce the chance of accidental tampering in deployment. This Spring.NET configuration file is shown below.

<objects xmlns="http://www.springframework.net" 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://www.springframework.net
         http://www.springframework.net/xsd/spring-objects.xsd" >
    
    <object name="productDao" type="DaoApp.SimpleProductDao, DaoApp ">
      <property name="maxResults" value="${maxResults}"/>
      <property name="dbConnection" ref="myConnection"/>
    </object>
    
    <object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data"> 
      <property name="connectionstring" value="${connection.string}"/> 
    </object>

    <object name="appConfigPropertyHolder" 
            type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">

        <property name="configSections">          
          <value>DaoConfiguration,DatabaseConfiguration</value>                              
        </property>              
       
    </object>
</objects>

The values of ${maxResults} and ${connection.string} match the key names used in the two NameValueSectionHandlers DaoConfiguration and DatabaseConfiguration. The PropertyPlaceholderConfigurer refers to these two sections via a comma delimited list of section names in the configSections property. If you are using section groups, prefix the section group name, for example myConfigSection/DaoConfiguraiton.

The PropertyPlaceholderConfigurer class also supports retrieving name value pairs from other IResource locations. These can be specified using the Location and Locations properties of the PropertyPlaceHolderConfigurer class.

If there are properties with the same name in different resource locations the default behavior is that the last property processed overrides the previous values. This is behavior is controlled by the LastLocationOverrides property. True enables overriding while false will append the values as one would normally expect using NameValueCollection.Add.

	Note
	In an ASP.NET environment you must specify the full, four-part name of the assembly when using a NameValueFileSectionHandler <section name="hibernateConfiguration" type="System.Configuration.NameValueFileSectionHandler, System, Version=1.0.3300.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

<object id="MyMovieFinder" type="${custom.moviefinder.type}"/>

<object id="TestObject" type="Simple.TestObject, MyAssembly">
  <property name="age" expression="${ageExpression}"/>
  <property name="spouse" ref="${spouse-ref}"/>
</object>

<object name="appConfigPropertyHolder" 
        type="Spring.Objects.Factory.Config.PropertyPlaceholderConfigurer, Spring.Core">
        <property name="configSections" value="DaoConfiguration,DatabaseConfiguration"/>
        <property name="EnvironmentVariableMode" value="Override"/>
    </object>
</objects>

The PropertyOverrideConfigurer, another object factory post-processor, is similar to the PropertyPlaceholderConfigurer, but in contrast to the latter, the original definitions can have default values or no values at all for object properties. If an overriding configuration file does not have an entry for a certain object property, the default context definition is used.

Note that the object factory definition is not aware of being overridden, so it is not immediately obvious when looking at the XML definition file that the override configurer is being used. In case that there are multiple PropertyOverrideConfigurer instances that define different values for the same object property, the last one will win (due to the overriding mechanism).

The example usage is similar to when using PropertyPlaceHolderConfigurer except that the key name refers to the name given to the object in the Spring.NET configuration file and is suffixed via 'dot' notation with the name of the property For example, if the application configuration file is

<configuration>
  <configSections>
    <sectionGroup name="spring">
      <section name="context" type="Spring.Context.Support.ContextHandler, Spring.Core"/>
    </sectionGroup>
    <section name="DaoConfigurationOverride" type="System.Configuration.NameValueSectionHandler"/>
  </configSections>

  <DaoConfigurationOverride>
    <add key="productDao.maxResults" value="1000"/>
  </DaoConfigurationOverride>
  
  <spring>
    <context>
      <resource uri="assembly://DaoApp/DaoApp/objects.xml"/>
    </context>
  </spring>

</configuration>

Then the value of 1000 will be used to overlay the value of 2000 set in the Spring.NET configuration file shown below

<objects xmlns="http://www.springframework.net" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
        xsi:schemaLocation="http://www.springframework.net http://www.springframework.net/xsd/spring-objects.xsd" >

    <object name="productDao" type="PropPlayApp.SimpleProductDao, PropPlayApp " >
      <property name="maxResults" value="2000"/>
      <property name="dbConnection" ref="myConnection"/>
      <property name="log" ref="daoLog"/>
    </object>
    
    <object name="daoLog" type="Spring.Objects.Factory.Config.LogFactoryObject, Spring.Core">
      <property name="logName" value="DAOLogger"/>
    </object>
    
    <object name="myConnection" type="System.Data.Odbc.OdbcConnection, System.Data"> 
      <property name="connectionstring"> 
        <value>dsn=MyDSN;uid=sa;pwd=myPassword;</value>
      </property> 
    </object> 

    <object name="appConfigPropertyOverride" type="Spring.Objects.Factory.Config.PropertyOverrideConfigurer, Spring.Core">
      <property name="configSections">          
        <value>DaoConfigurationOverride</value>                              
      </property> 
    </object>

</objects>

The IVariableSource is the base interface for providing the ability to get the value of property placeholders (name-value) pairs from a variety of sources. Out of the box, Spring.NET supports a number of variable sources that allow users to obtain variable values from .NET config files, java-style property files, environment variables, command line arguments and the registry and the new connection strings configuration section in .NET 2.0. The list of implementing classes is listed below. Please refer to the SDK documentation for more information.

You use this by defining an instance of Spring.Objects.Factory.Config.VariablePlaceholderConfigurer in your configuration and set the property VariableSource to a single IVariableSource instance or the list property VariableSources to a list of IVariableSource instances. In the case of the same property defined in multiple IVariableSource implementations, the first one in the list that contains the property value will be used.

<object type="Spring.Objects.Factory.Config.VariablePlaceholderConfigurer, Spring.Core">
   <property name="VariableSources">
      <list>
         <object type="Spring.Objects.Factory.Config.ConfigSectionVariableSource, Spring.Core">
            <property name="SectionNames" value="CryptedConfiguration" />
         </object>
      </list>
   </property>
</object>
        

The IVariableSource interface is shown below

public interface IVariableSource
{
  string ResolveVariable(string name);
}

This is a simple contract to implement if you should decide to create your own custom implemention. Look at the source code of the current implementations for some inspiration if you go that route. To register your own custom implemenation, simply configure VariablePlaceholderConfigurer to refer to your class.

• object GetObject(): has to return an instance of the object this factory creates. The instance can possibly be shared (depending on whether this factory provides singletons or prototypes).

• bool IsSingleton: has to return true if this IFactoryObject returns singletons, false otherwise.

• Type ObjectType: has to return either the object type returned by the GetObject() method or null if the type isn't known in advance.

The Spring.Objects.Factory.IConfigurableFactoryObject interface inherits from IFactoryObject interface and adds the following property.

IConfigurableFactoryObject implementions you already have examples of in Section 27.3, “Client-side” are WebServiceProxyFactory.

• string GetMessage(string name): retrieves a message from the IMessageSource and using CurrentUICulture.

• string GetMessage(string name, CultureInfo cultureInfo): retrieves a message from the IMessageSource using a specified culture.

• string GetMessage(string name, params object[] args): retrieves a message from the IMessageSource using a variable list of arguments as replacement values in the message. The CurrentUICulture is used to resolve the message.

• string GetMessage(string name, CultureInfo cultureInfo, params object[] args): retrieves a message from the IMessageSource using a variable list of arguments as replacement values in the message. The specified culture is used to resolve the message.

• string GetMessage(string name, string defaultMessage, CultureInfo culture, params object[] arguments): retrieves a message from the IMessageSource using a variable list of arguments as replacement values in the message. The specified culture is used to resolve the message. If no message can be resolved, the default message is used.

• string GetMessage(IMessageSourceResolvable resolvable, CultureInfo culture) : all properties used in the methods above are also wrapped in a class - the MessageSourceResolvable, which you can use in this method.

• object GetResourceObject(string name):Get a localized resource object, i.e. Icon, Image, etc. given the resource name. The CurrentUICulture is used to resolve the resource object.

• object GetResourceObject(string name, CultureInfo cultureInfo):Get a localized resource object, i.e. Icon, Image, etc. given the resource name. The specified culture is used to resolve the resource object.

• void ApplyResources(object value, string objectName, CultureInfo cultureInfo): Uses a ComponentResourceManager to apply resources to all object properties that have a matching key name. Resource key names are of the form objectName.propertyName

• void PublishEvents( object sourceObject ): publishes all events of the source object to subscribers that implement the correct handler methods.

• void Subscribe(object subscriber ): The subscriber receives all events from the source object for which it has matching handler methods.

• void Subscribe(object subscriber, Type targetSourceType ): The subscriber receives all events from a source object of a particular type for which it has matching handler methods.

• void Unsubscribe(object subscriber ): Unsubscribe all events from the source object for which it has matching handler methods.

• void Unsubscribe(object subscriber, Type targetSourceType ): Unsubscribe all events from a source object of a particular type for which it has matching handler methods.