Performing an action when Windows shuts down a Delphi app
From: wesjones@hooked.net (Wes Jones)
I did a little investigation, and here is what seems to be happening:
Normally, when you exit a Delphi application by using the system menu or by calling the Form's Close method, the following event handlers are called:
FormCloseQuery - the default action sets the variable CanClose=TRUE so form close will continue.
FormClose
FormDestroy
If the application is active and you attempt to exit Windows, the event handlers are called in the following sequence:
FormCloseQuery
FormDestroy
The FormClose method never seems to be called.
Here is the flow of events when the user chooses to end the Windows session:
Windows sends out a WM_QUERYENDSESSION message to all application windows one by one and awaits a response
Each application window receives the message and returns a non-zero value if it is OK to terminate, or 0 if it is not OK to terminate.
If any application returns 0, the Windows session is not ended, otherwise, Windows sends a WM_ENDSESSION message to all application windows
Each Application Window responds with a TRUE value indicating that Windows can terminate any time after all applications have returned from processing this message. This appears to be the location of the Delphi problem: Delphi applications seem to return TRUE and the FormDestroy method is called immediately, bypassing the FormClose method.
Windows exits
One solution is to respond to the WM_QUERYENDSESSION message in the Delphi application and prevent Windows from exiting by returning a 0 result. This can't be done in the FormCloseQuery method because there is no way to determine the source of the request (it can either be the result of the WM_QUERYENDSESSION message or the user just simply closing the application).
Another solution is to respond to the WM_QUERYENDSESSION message by calling the same cleanup procedure you call in the FormClose method.
Example:
--------------------------------------------------------------------------------
unit Unit1;
interface
uses
SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls, Forms,
Dialogs;
type
TForm1 = class(TForm)
procedure FormClose(Sender: TObject; var Action: TCloseAction);
private
{---------------------------------------------------------------}
{ Custom procedure to respond to the WM_QUERYENDSESSION message }
{---------------------------------------------------------------}
procedure WMQueryEndSession(
var Message: TWMQueryEndSession); message WM_QUERYENDSESSION;
public
{ Public declarations }
end;
var
Form1 : TForm1;
implementation
{$R *.DFM}
{---------------------------------------------------------------}
{ Custom procedure to respond to the WM_QUERYENDSESSION message }
{ The application will only receive this message in the event }
{ that Windows is requesing to exit. }
{---------------------------------------------------------------}
procedure TForm1.WMQueryEndSession(var Message: TWMQueryEndSession);
begin
inherited; { let the inherited message handler respond first }
{--------------------------------------------------------------------}
{ at this point, you can either prevent windows from closing... }
{ Message.Result:=0; }
{---------------------------or---------------------------------------}
{ just call the same cleanup procedure that you call in FormClose... }
{ MyCleanUpProcedure; }
{--------------------------------------------------------------------}
end;
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
MyCleanUpProcedure;
end;
end.