Author: Radikal Q3 


When the user closes Windows having our application opened, it is possible that 
occur in a wrong moment (without recording data, in the middle of a process, etc).

Answer:

This can be avoided capturing the message that send Windows to all the applications 
when the user wants to close Windows: the  message WM_QUERYENSESSION
 
To capture the message and to send it to our treatment code of the message:
1   
2        TForm1 = class(TForm)
3        ..........
4          private
5            procedure WMQueryEndSession(var Msg: TWMQueryEndSession); message 
6   WM_QUERYENDSESSION;
7        ..........
8        end; 


Simply...we must add the next line in the Private part of the form:
9   
10      procedure WMQueryEndSession(var Msg: TWMQueryEndSession); message 
11  WM_QUERYENDSESSION; 


and later, in the implementation, we put the treatment code of the message:
12  
13  procedure TForm1.WMQueryEndSession(var Msg: TWMQueryEndSession);
14  begin
15    MessageBox(Handle, 'Cierra antes el programa', nil, MB_OK);
16    Msg.result := 0;
17  end;


If instead of aborting the close of Windows, we want that follows being 
accomplished, enough with which we change the Msg.result:=0 for Msg.result:=1.
 
NOTE: The behavior of the message defers in win98 and WinNT, as soon as watches you the help of the message WM_QUERYENDSESSION.