Find out what's closing your application

Introduction

You can use this code to see why your application is closing (closed by user, by Windows, by code?). It can be very handy if you are using a NotifyIcon in your app. You can figure out if the user is closing your app or not, if so, then you can just minimize it to tray.

For those who have used Visual Basic before, you know that there was a QueryUnload method for your Forms and that you could find out the reason for the form's closing by examining the UnloadMode variable.

This code snippet shows you how to do this in .NET. The sample code is in VB.NET. The code is from GotDotNet message boards, written by "YeahIGotDotNet".

Private Sub Form1_Closing(ByVal sender As Object, _
  ByVal e As System.ComponentModel.CancelEventArgs) _
  Handles MyBase.Closing
    Dim O As System.Diagnostics.StackTrace = _
           New System.Diagnostics.StackTrace(True)
    Dim F As System.Diagnostics.StackFrame

    F = O.GetFrame(7)

    Select Case F.GetMethod.Name.ToString
        Case "SendMessage"
            MsgBox("Closing because of call in code.")
        Case "CallWindowProc"
            MsgBox("Closing because of system menu click.")
        Case "DispatchMessageW"
            MsgBox("Closing because of Task Manager.")
        Case Else
            MsgBox("Don't Know why I'm closing!!??")
    End Select
End Sub

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MrPolite

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Handles Mybase.closing

atogwe

9:04 11 Jun '07

Using WM_QUERYENDSESSION to detect Windows shutdown

rodgerc

9:13 2 Oct '06

Overriding WndProc changes the GetMethod.Name properties

HanreG

3:15 7 Nov '03

Coversion of C++ method

BogBrush Zone

5:12 31 Aug '03

More complete implementation

EvilDoctorSmith

9:23 28 Oct '02

I don't really have time to write an article on this, but here is a more complete implementation. I have tested on Windows 2000 only, so it may not work on 98/ME. Also, this has not been tested with MDI children or parents.

Most times, you need to know if you are closing because the user selects "Close" from the menu, or whether it is some sort of system thing. The previous implementation does not take into account shutting down the computer. In this instance, where I am cancelling and hiding if it is user input, this would abort the shutdown! You'd never be able to shutdown your computer normally as long as your .NET program is running.

private enum ClosingSource
{
    Unknown         = -1, //We've never seen this one before!!!
    Code            = 0,  //Shutdown from a call to this.Close();
    TaskManager     = 1,  //Shutdown from the task manager. 
    SystemShutdown  = 2,  //Windows is shutting down, or user logging out.
    FormControlMenu = 3   //User selected by clicking "X" in form, or from
                          //    the control menu.
}
 
private ClosingSource GetClosingSource(StackTrace stack)
{
    StackFrame frame7 = stack.GetFrame(7);
    if(frame7.GetMethod().Name == "SendMessage")
        return ClosingSource.Code;
    else if(frame7.GetMethod().Name == "DispatchMessageW")
        return ClosingSource.TaskManager;
    else if(frame7.GetMethod().Name == "CallWindowProc")
    {
        //At frame 7, a close due to system shutdown still looks
        //like a user-selected shutdown, so we have to check the
        //next change, which is at stack position 14.
        StackFrame frame14 = stack.GetFrame(14);
        if(frame14.GetMethod().Name == "WndProc")
            return ClosingSource.SystemShutdown;
        else if(frame14.GetMethod().Name == "WmSysCommand")
            return ClosingSource.FormControlMenu;
    }
			
    return ClosingSource.Unknown;
}
 
private void EventLog_Closing(object sender, System.ComponentModel.CancelEventArgs e)
{
    StackTrace stack = new StackTrace(true);
 
    ClosingSource source = GetClosingSource(stack);
 
    if(source == ClosingSource.FormControlMenu)
    {
        e.Cancel = true;
        this.Hide();
    }
}

I don't like the stack-based solution for "QueryUnload" --> "Closing" much. It depends on a lot of underlying code that I don't have any control over not changing over time. However, I have yet to find a better method, or even another method that works. One of the few instances where .NET functionality is not a superset of VB6.