Executing Code when Setting Properties

You can create Property Let, Property Set, and Property Get procedures that share the same name. By doing this, you can create a group of related procedures that work together. Once a name is used for a Property procedure, that name can’t be used to name a Sub or Function procedure, a variable, or a user-defined type.

The Property Let statement allows you to create a procedure that sets the value of the property. One example might be a Property procedure that creates an inverted property for a bitmap on a form. This is the syntax used to call the Property Let procedure:

Form1.Inverted = True

The actual work of inverting a bitmap on the form is done within the Property Let procedure:

Private IsInverted As Boolean

Property Let Inverted(X As Boolean)
    IsInverted = X
    If IsInverted Then
        …
        (statements)
    Else
        (statements)
    End If
End Property

The form-level variable IsInverted stores the setting of your property. By declaring it Private, the user can only change it only using your Property Let procedure. Use a name that makes it easy to recognize that the variable is used for the property.

This Property Get procedure is used to return the current state of the Inverted property:

Property Get Inverted() As Boolean
    Inverted = IsInverted
End Property

Property procedures make it easy to execute code at the same time the value of a property is set. You can use property procedures to do the following processing:

• Before a property value is set to determine the value of the property.
  
  
• After a property value is set, based on the new value.