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 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 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.

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