Step 5: Export methods to create class instances

Step 5: Export methods to create class instances

PowerBuilder creates nonvisual and visual class instances differently:

• For visual classes, the instance is created when the window or visual control in which the class is used is opened. See "Creating visual class instances".

• For nonvisual classes, the instance is created when the PowerBuilder CREATE statement is used. This is described next.

When the PowerBuilder application creates an instance of a nonvisual class using the PowerScript CREATE statement, the PBVM calls the PBX_CreateNonVisualObject method in the extension. Every extension that contains nonvisual native classes must export this method.

In the same way that multiple classes are included in a single description passed by PBX_GetDescription, PBX_CreateNonVisualObject can be used to create multiple classes.

In this example, the extension has three classes. An IF statement compares the name of the class passed in from the PowerBuilder CREATE statement to the name of each of the classes in the extension in turn and creates an instance of the first class with a matching name. You could also use a CASE statement. The class name in the string comparison must be all lowercase:

PBXEXPORT PBXRESULT PBXCALL PBX_CreateNonVisualObject(
   IPB_Session * session, 
   pbobject obj, 
   LPCSTR className, 
   IPBX_NonVisualObject **nvobj
)
{
   PBXRESULT result = PBX_OK;
   // The class name must not contain uppercase
   if ( strcmp( className, "classone" ) == 0 )
      *nvobj = new ClassOne;
   else if ( strcmp( className, "classtwo" ) == 0 )
      *nvobj = new ClassTwo( session );
   else if ( strcmp( className, "classthree" ) == 0 )
      *nvobj = new ClassThree;
   else
   {
      *nvobj = NULL;
      result = PBX_E_NO_SUCH_CLASS;
   }
   return PBX_OK;
};