How to Manage the Exiting Process with QueryUnLoad Event

MORE INFORMATION

As described in the Help menu, the QueryUnload event occurs before the Destroy event. The ReleaseType property is set prior to the QueryUnload event being called. The QueryUnload event occurs when:

• The CLEAR WINDOWS, RELEASE WINDOWS, or QUIT command is executed in code.
• The user double-clicks the Control-menu box.
• The user chooses Close from the Control menu on a Form.

QueryUnload is where you should put your exit confirmation dialog box to verify that the user really wants to leave. The QueryUnload event uses a related property, the ReleaseType property, to indicate how the user is exiting. This is a particularly useful for users choosing the Close option from the Control menu on a form.

The following table summarizes the values for the ReleaseType property and indicates when the QueryUnload event is called.

Action                 ReleaseType Value    QueryUnload Called?
---------------------------------------------------------------
QUIT                   2                    Yes
CLEAR WINDOWS          1                    Yes
RELEASE WINDOWS        1                    Yes
Click in Close Box     1                    Yes
RELEASE thisform       0                    No
				

Note that the QueryUnload event is not called when a RELEASE thisform command is called. Therefore, if you are using the RELEASE thisform command as a means of exiting a form, you won't be able to use the code example below in the QueryUnload event; you'll need to use an alternate method to achieve the same result.

Code Sample

The following code sample demonstrates how to use the QueryUnload event in a form:

   *--------------------------------------------------------------*
   * Program: QUNLDTST - QueryUnload test code                    *
   * Purpose: Demonstrates trapping user exit from form.      *
   *--------------------------------------------------------------*
   cMessageTitle = 'Test'
   cMessageText  = 'Did you *really* mean to close this form?'
   nDialogType   = 4 + 32 + 256
   *  4   = Yes and No buttons
   *  32  = Question mark icon
   *  256 = Second button is default
   nAnswer = MESSAGEBOX(cMessageText, nDialogType, cMessageTitle)
   DO CASE
     CASE nAnswer = 6
       RELEASE THISFORM
     CASE nAnswer = 7
       NODEFAULT
   ENDCASE
				

The use of NODEFAULT in the DO CASE construction overrides the default action of closing the form, in effect canceling the user's actions.