Для чего нужно событие Form_QueryUnload

Visual Basic Reference
Visual Studio 6.0
QueryUnload Event

Occurs before a form or application closes. When an MDIForm object closes, the QueryUnload event occurs first for the MDI form and then in all MDI child forms. If no form cancels the QueryUnload event, the Unload event occurs first in all other forms and then in an MDI form. When a child form or a Form object closes, the QueryUnload event in that form occurs before the form's Unload event.

Syntax

Private Sub Form_QueryUnload(cancel As Integer, unloadmode As Integer)

Private Sub MDIForm_QueryUnload(cancel As Integer, unloadmode As Integer)

The QueryUnload event syntax has these parts:Part Description
cancel An integer. Setting this argument to any value other than 0 stops the QueryUnload event in all loaded forms and stops the form and application from closing.
unloadmode A value or constant indicating the cause of the QueryUnload event, as described in Return Values.



Return Values

The unloadmode argument returns the following values:

Constant	Value	Description
vbFormControlMenu	0	The user chose the Close command from the Control menu on the form.
vbFormCode	1	The Unload statement is invoked from code.
vbAppWindows	2	The current Microsoft Windows operating environment session is ending.
vbAppTaskManager	3	The Microsoft Windows Task Manager is closing the application.
vbFormMDIForm	4	An MDI child form is closing because the MDI form is closing.
vbFormOwner	5	A form is closing because its owner is closing.

These constants are listed in the Visual Basic (VB) object library in the Object Browser.

Remarks

This event is typically used to make sure there are no unfinished tasks in the forms included in an application before that application closes. For example, if a user has not yet saved some new data in any form, your application can prompt the user to save the data.

When an application closes, you can use either the QueryUnload or Unload event procedure to set the Cancel property to True, stopping the closing process. However, the QueryUnload event occurs in all forms before any are unloaded, and the Unload event occurs as each form is unloaded.