Microsoft KB Archive/69792

= How to Trap VB Form Lost Focus with GetActiveWindow API =

Article ID: 69792

Article Last Modified on 11/18/2003

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APPLIES TO


 * Microsoft Visual Basic 1.0 Standard Edition
 * Microsoft Visual Basic 2.0 Standard Edition
 * Microsoft Visual Basic 3.0 Professional Edition

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This article was previously published under Q69792



SUMMARY
The LostFocus event in Microsoft Visual Basic is useful when transferring control within an application, and you can use the form deactivate and activate events in versions 2.0 and 3.0 to see if the entire form has lost the focus. However, in version 1.0, no global routine exists to check for the entire form losing the focus. To check whether your version 1.0 application has lost the focus, periodically check the Windows API function GetActiveWindow in a Visual Basic timer event, as explained below.



MORE INFORMATION
The only way that version 1.0 provides a check for loss of focus on a form or control is by triggering the LostFocus event. A form does support a LostFocus event; however, a form will only get focus if there are no controls on that form. Focus goes to the controls on a form, and when you click any other visible form, the control's LostFocus procedure will be called. A control's LostFocus procedure will also be called when another control on the form is activated. To perform a routine that occurs only when the form loses focus requires careful management of what generated a LostFocus event on each control (such as setting a flag if another control's Click event was called).

For a simpler method to check if a whole form has lost the focus, you can call the Windows API function GetActiveWindow, located in USER.EXE (a DLL provided with Windows 3.0). The GetActiveWindow API call returns the window handle of the currently active window, which is the new window that you last clicked anywhere in Microsoft Windows. In a timer event procedure for the form, call GetActiveWindow and compare the handle of the currently active Window with the handle of the form window (Form1.hWND). If the handle differs, you know the form has lost the focus. The following program example demonstrates this technique:

Program Example
This single-form example will print &quot;Lost Focus&quot; on the form when you click a different window (such as when you click another program running in Windows).

In Visual Basic, draw one timer control (Timer1) and one command button (Command1) on a single form (Form1).

From the VB.EXE Code menu, choose View Code, and enter the following code for Form1, using (general) from the Object box, and (declarations) from the Procedure box:

Declare Function GetActiveWindow Lib &quot;User&quot; As Integer Dim FOCUS As Integer Const TRUE = -1 Const FALSE = 0

From the Object box, choose Timer1, and from the Procedure box, choose Timer, and then put the following code in the Timer1_Timer procedure:

Sub Timer1_Timer If FOCUS = TRUE Then ' Compare the handle of the currently active Window with the handle ' of the Form1 window: If GetActiveWindow <> Form1.hWND Then 'Do form's lost-focus routines here. Print &quot;Lost Focus&quot; FOCUS = FALSE End If  End If End Sub

You must set FOCUS=TRUE in the Click event procedure of every control on the form, as follows:

From the Object box, choose Command1, and from the Procedure box, choose Click, then put the following code in the Command1_Click procedure:

Sub Command1_Click FOCUS = TRUE End Sub

Double-click Form1 (at design time) and enter the following code for the Form_Click procedure:

Sub Form_Click FOCUS = TRUE Timer1.Interval = 10 End Sub

You can now run the program.

