Differences Among Form's Initialize, Load, and Activate Events (138819)

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Initialize

This event fires only when an application first creates an instance of a form. In an application with a startup form, the first event that occurs is the startup form's Initialize event. Initialize may also be called well in advance of a Load or Show if, for example, the following statement is executed:

   Set x = New Form1
				

In addition, Initialize is called again if all of the references to the form have been previously set to Nothing and the form is then loaded, shown or has a variable set to it (for example, Set x = New Form1).

Many of the tasks previously done in the Form_Load statement can, in Visual Basic 4.0, be performed in the Form_Initialize statement. Any statement that needs to be performed a single time when a form is created can be done here. Be careful that you do not reference any of the properties of the controls on the form because doing so will cause an automatic Form_Load.

Load

The Form_Load event fires when a form is first loaded into memory. A form can be caused to load by an explicit Load statement, by calling a Show method when the form is not already loaded, or by a line of code in another module making a reference to any of the unloaded form's properties (or to any properties of the unloaded form's children).

For example, if Form2 is not loaded, and a subroutine in Form1 executes a line of code setting or reading Form2's Caption property, then Form2 will be loaded into memory, and the corresponding Form2_Load event will be called. Unless a form is loaded as a result of a Show method or has its Visible property set to True, the form will be loaded into memory but will not be made visible. Forms can be hidden and shown (using the Hide and Show methods) while remaining in memory; the Load event will only be fired when the form is first loaded.

Some procedures and methods of controls (for example, the SetFocus method) require that their parent form be loaded before they are called. In this situation, the best thing to do is to perform an explicit Form.Show in the Form_Load event, and do any such initialization after calling the Show method. This is preferable to doing the initialization in, for example, the Form_Activate event because Activate is called every time the user switches between forms in an application. Also, if you are calling related events, such as Activate, Paint, or Resize, be careful that their actions do not conflict with the Load and that they don't fire recursive events.

Activate

As was stated previously, the Activate event is called every time a form becomes the active window, as long as the focus has moved between forms in the application. The Activate event is not called if the previous window that had the focus was outside of the application.

There are fewer caveats with Activate than with the previous two event procedures, perhaps because Activate is marginally less important than the Initialize and Load events. Code that needs to be executed every time the focus changes within an application should reside in the form's activate event.