Call C# Function when application is ended usingTask Manager

Incidentally, if you're wondering what happens if the user closes the form by pressing the X button or via the control menu, then the answer is that these actions generate the WM_SYSCOMMAND message 0x112 rather than the WM_CLOSE message 0x10.

So there's no problem trapping these actions and the only ones where you need to set CloseReason.User manually are those where the form is closed programatically.

As it explains in the link, message 0x10 corresponds to both CloseReason.EndTask and CloseReason.User.

So to determine which applies you have to set CloseReason to EndTask by default and then when the user performs some action such as clicking a button to close the form, you have to manually set CloseReason to User.

If CloseReason is still set to EndTask when the form closes then it must have been closed via Task Manager.

It's not very satisfactory but it seems to be the only way to do it.

this code is not working properly.
It does not show any type of message that application is going to close, when the application is closed using Task Manager.

In Windows Forms this is easy because when you handle the FormClosing or FormClosed event on the main form, the FormClosingEventArgs or FormClosedEventArgs passed to the handler has a CloseReason property.

Unfortunately, the Window.Closing or Closed event in WPF doesn't have this and you therefore have to resort to examining the underlying Win32 mesage to get this information.

I found this thread which explains how to do it:

http://social.msdn.microsoft.com/Forums/en-US/wpf/thread/549a4bbb-e77b-4c5a-b724-07996774c60a