ID Number: Q74474
3.00
WINDOWS
Summary:
An application cannot destroy the parent of a modal dialog box. When
the modal dialog box ends, control is returned to its parent. If the
parent is destroyed, control is given to a non-existent window and the
application crashes.
When a parent window receives the destroy message, it is too late to
destroy a child modal dialog box. The destroyed dialog box does not
return control until after all the existing messages are processed,
including the final destruction of the parent window.
Therefore, it is imperative that all generational parents of a modal
dialog box be disabled and have no way of receiving a WM_DESTROY
message while the modal dialog box is active.
This situation does not affect modeless dialog boxes. Therefore, if
the design of a system cannot rule out the above problem, use a
modeless dialog box instead of a modal dialog box.
Because the Task Manager can kill any program at any time, there is no
absolute protection from the parent being closed. The optimal solution
is to forgo modal dialog boxes in favor of modeless dialog boxes.
When a modeless dialog box is created, it may disable its parental
windows.