Is there a better way to handle the task of doing something after the user has chosen to exit a WinForms program than this :
[edit 1 : in response to comment by 'NoBugz] In this case there is no ControlBox on the Form, and there is a reason for putting one level of indirection in what happens when the user chooses to close the Form [/edit 1]
[edit 2 : in response to all comments as of GMT +7 18:35 January 20 ] Perhaps using fading out the MainForm is a simple illustration of what you might want do as the Application is being closed : the user cannot interact with that : it is self-evidently related to the user's decision to terminate the application. [/edit 2]
(use some form of threading ?) (implications for a multi-threaded app ?) (does this code "smell bad" ?)
// 'shutDown is an external form-scoped boolean variable
//
private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
// make sure we don't block Windows ShutDown
// or other valid reasons to close the Form
if (e.CloseReason != CloseReason.ApplicationExitCall) return;
// test for 'shutDown flag set here
if (shutDown) return;
// cancel closing the Form this time through
e.Cancel = true;
// user choice : default = 'Cancel
if (MessageBox.Show("Exit Application ?", "", MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2) == System.Windows.Forms.DialogResult.OK)
{
// user says Exit : activate Timer, set the flag to detect Exit
timer1.Enabled = true;
shutDown = true;
}
}
Summary : In a very standard WinForms application (one MainForm launched in Program.cs in the standard way) : in the FormClosing Event handler of the MainForm :
exit immediately (triggering the default behavior : which is to close the MainForm and exit the Application) if :
a. the CloseReason is anything other CloseReason.ApplicationExitCall
b. if a special boolean variable is set to true, or
if no immediate exit : cancel the "first call" to FormClosing.
the user then makes a choice, via MessageBox.Show dialog, to Exit the Application, or Cancel :
a. if the user Cancels, of course, the Application stays "as is."
b. if the user has chosen to 'Exit :
set the special boolean flag variable to true
run a Timer that does some special stuff.
when the internal test in the Timer code detects the "special stuff" is done, it calls Application.Exit
My suggestions, both as a developer and a user:
A very fast task
Just do the task in the Closing event handler.
A less fast, but not incredibly slow task
Create a non-background thread (so it's not shut down when the application exits) with the task in the Closing event handler.
Let the application exit. Forms will go away, et cetera, but the process will keep running until the task is done.
Just remember to handle exceptions and such in that worker thread. And make sure that things doesn't crash if the user reopens your application before that task is done.
Slower tasks
In the Closing event handler, open a shutting-down-form and let the form itself close.
Do the task in the/behind the shutting-down-form while displaying some friendly progress and information.
Exit application when task is done.
Some untested example code. We are doing something similar to this in one of our applications. The task in our case is to store window properties (location, size, window state, et cetera) to a database.
private void MainForm_FormClosing(object sender, FormClosingEventArgs e)
{
// If it wasn't the user who asked for the closing, we just close
if (e.CloseReason != CloseReason.UserClosing)
return;
// If it was the user, we want to make sure he didn't do it by accident
DialogResult r = MessageBox.Show("Are you sure you want this?",
"Application is shutting down.",
MessageBoxButtons.YesNo,
MessageBoxIcon.Question);
if (r != DialogResult.Yes)
{
e.Cancel = true;
return;
}
}
protected override void OnFormClosed(FormClosedEventArgs e)
{
// Start the task
var thread = new Thread(DoTask)
{
IsBackground = false,
Name = "Closing thread.",
};
thread.Start();
base.OnFormClosed(e);
}
private void DoTask()
{
// Some task to do here
}
I don't see anything "wrong" with this. My only recommendation would be to let the user know that the program is "shutting down" by raising a non-modal window or perhaps a notification toaster above the system tray.
A couple of minor points:
I'd question the need for a timer: as the application is exiting anyway, and the user won't therefore expect the UI to be responsive, why not simply do the clean-up code on the UI thread? As suggested by #Dave Swersky, a little notification window during cleanup would be polite.
What happens if the application exit is triggered by a Windows shutdown or a user logoff?
Related
i am writing an application which use microscope.
When the user close the application, the application turned off the microscope.
Is there a way to execute this code when the application is closed because the user close the windows session ?
Regards,
You can use the FormClosing event to catch a form closing action, and perform tasks before closure, or prevent it from closing at all. Here is an example I use regularly.
private void Form_FormClosing(Object sender, FormClosingEventArgs e)
{
//Do stuff here:
if (prevent_close)
{
//or cancel the closing here:
e.Cancel = true;
}
}
Lately I have been having problems with my application not shutting down properly. After it has been told to exit, when I look in the Task Manager the process is still running, and I am unable to kill the process.
Suddenly I realized a strange pattern. The shutdown problem only appeared if I had opened a OpenFileDialog anytime when the application was running. I debugged a bit and saw that some threads did not shut down after the application should have exited. Also, to my surprise, when I invoked OpenFileDialog.ShowDialog(), it spawned a lot of threads (See the pictures below). The threads are alive throughtout the lifetime of the application.
Why does OpenFileDialog spawn so many threads? And why are they not closed after the file dialog is closed.
How does the OpenFileDialog problem relate to my shutdown problem...?
Threads just before openFileDialog.ShowDialog():
Threads while the dialog is open:
Threads right after openFileDialog.ShowDialog() has returned:
Threads hanging after the application has been shut down:
Code for opening the dialog:
private void startAllSequenceToolStripMenuItem_Click(object sender, EventArgs e)
{
OpenFileDialog ofn = new OpenFileDialog();
DialogResult result = ofn.ShowDialog();
if (result == DialogResult.Cancel)
return;
MessageBox.Show("do stuff");
}
I search the web for this and found nothing but I fixed by issue by calling Dispose. Code below:
private void startAllSequenceToolStripMenuItem_Click(object sender, EventArgs e)
{
OpenFileDialog ofn = new OpenFileDialog();
DialogResult result = ofn.ShowDialog();
if (result == DialogResult.Ok)
{
MessageBox.Show("do stuff");
}
// This one line seems to allow my application to exit cleanly in debug and release.
// But I don't instantiate a new object.
// I used the control on the form and called Dispose from form_closing.
ofn.Dispose();
}
This thread OpenFileDialog/c# slow on any file. better solution? has some half decent answers. All in all, as a last resort check with ProcExp from sysinternals. Also, is it only slow in the debugger? If so I wouldn't worry about it since it doesn't affect your users. Just make sure to isolate from your other code so your team is not constantly tripping over it in the debugger since it is slow.
If the user closes the Application a Save-File-Message have to be shown (to be sure that he wants to discard the changes of edited files).
to implement this, i have a menuitem with a command-binding (without key-gesture):
private void Command_Exit(object sender, ExecutedRoutedEventArgs e)
{
Application.Current.Shutdown();
}
the mainwindow has a closing-event. in this event i check if there unsaved files. if yes, the savedialog has to be opened (to choose, which files have to be saved):
private void Window_Closing(object sender, CancelEventArgs e)
{
if (sdl.Count() > 0)
{
SaveDialog sd = new SaveDialog();
IEnumerable<Doc> close = sd.ShowDialog(this);
if (close == null)
e.Cancel = true;
else
foreach (Doc document in close)
document.Save();
}
}
in this ShowDialog-Method (implemented in my SaveDialog-Class) i call
bool? ret = ShowDialog();
if (!ret.HasValue)
return null;
if (!ret.Value)
return null;
The problem is:
If i use the Alt+F4-Shortcut to close the Application (default-behaviour of the mainwindow) it works and i get the savedialog if there are unsaved files. but if i close the application by executing the Command_Exit-Method, the Method-Call
bool? ret = ShowDialog();
returns null and the dialog does not appear.
If i assign the Alt+F4 KeyGesture to the CommandBinding, the problem is switched: Executing Command_Exit works well but Alt+F4 Shortcut not.
What is the reason that the ShowDialog()-Method works not in both cases and how to fix it?
The Application.Current.Shutdown route allows you to listen for the shutdown request by handling the Exit event as detailed here:
http://msdn.microsoft.com/en-us/library/ms597013.aspx
It doesn't detail how it closes windows, so I wouldn't necessarily be convinced that the closing event handler would fire before it closes the application.
The other very standard way to shut the application down is to close the main window (the one shown at the very beginning). This would likely be the Window.Close method, if you are in the context of the window already, just call Close(). This will then hit the closing event handler.
Your Command_Exit implementation is wrong. Application.Current.Shutdown() means that the application is already shutting down, which can prevent the dialogs from opening.
You should implement the command other way: in the command you should ask your business logic if it's safe to shutdown, and issue Application.Current.Shutdown() only in that case. Otherwise, you should ask the business logic to start the shutdown sequence, which would in turn save the open files, and issue a Shutdown upon completing save operations.
Moreover, you should trigger the same routine when the user tries to close the main window (that is, on its Window.Closing).
The requirements I'm up against
About 12 people are using this application, but we only want to allow 4 to close the application through traditional methods (Alt+F4, File > Exit, Close)
If any other method is used (TaskManager, WindowsShutdown) or one of the allowed users close the application, we need to perform some clean up (Closing out some connection channels)
The Code I've used to satisfy said requirements
private void formClosing(object sender, FormClosingEventArgs e)
{
// If a user is allowed to close the application, an empty file (filename)
// will be in the root directory of the application.
if(e.CloseReason == CloseReason.UserClosing && !File.Exists("filename"))
{
e.Cancel = true;
return;
}
// Cleanup
}
The Problem
If a user (not allowed to close) attempts to close the application through traditional methods, then attempts to close using Task Manager the CloseReason enum doesn't seem to reset itself, thus causing Task Manager to pop the prompt to force close, preventing the application from cleaning up.
The Question
Is this a bug, or am I missing something, something that will reset the CloseReason after the FormClosing event has been cancelled.
.NET Reflector is your friend when working out how WinForms is operating.
The Form class has an internal field called closeReason and this is used when generating the event parameter that you examine in the Closing event. This internal field is set in four different places that I can find. These are...
1, The Form.Close() method sets the closeReason = UserClosing.
This makes sense as making a manual call to the Form.Close() method is usually the result of some user action, such as a File->Exit menu option being selected by the user. Clearly this is a user action.
2, The WM_SYSCOMMAND (SC_CLOSE) sets the closeReason = UserClosing.
The WndProc of the Form processes the SC_CLOSE system command by setting the closeReason to UserClosing and the lets the default window proc execute and close the application. This makes sense as this SC_CLOSE is sent when the user presses the window close chrome button or selected the close option from right clicking the title bar. Both are user actions and so setting the closeReason to UserClosing appears correct.
3, WndProc processes message WM_CLOSE (0x10) with closeReason = TaskManagerClosing
WM_CLOSE is sent by task manager and other applications to close a window and if the closeReason is currently equal to None it updates it to TaskManagerClosing. Note this issue with it being updated only if it is None as I think this is a problem for you.
4, WndProc processes messages 0x11 and 0x16 with closeReason = WindowsShutDown
This is not very interesting as you do not care about this scenario but it is just standard processing of shut down messages.
So the core problem you are having is that at no point is the closeReason being reset back to None when you cancel the Closing event. Therefore point number 3 above will never correctly update the value to TaskManagerClosing if that occurs after your cancel. As the closeReasson is an internal field you cannot update it directly. But you can cheat and this is an approach I have used myself in the past. You need to use reflection to get access to the internal field and then reset it to None when you set Cancel=true in your event handler.
I have not tested this code but you need something along the lines of...
PropertyInfo pi = typeof(Form).GetProperty("CloseReason",
BindingFlags.Instance |
BindingFlags.SetProperty |
BindingFlags.NonPublic);
pi.SetValue(this, CloseReason.None, null);
I think you cannot keep your process from shutting down if it's initiated by task manager (that is, OS... he's the 'big boss', it doesn't make sense that you can deny it something like closing your program).
The next best thing is to record the state of the application, and then instantiate another instance of your process with some startup options to take over the state you left. The OS would kill your process, but you will start another one immediately.
Also, if the user clicks in TaskManager "go to process" in the app list, and from there ends process, I don't think you'll be receiving any event at all...
Maybe it would be best if you had a windows service that's running behind the scenes and that keeps track that an instance is running. This way, users probably won't be aware that such process exists since it's not their application, and you can use that keep track of application shutdown.
I have an application that has been getting strange errors when canceling out of a dialog box. The application can't continue if the box is cancelled out of, so it exits, but it is not working for some reason, and thus it keeps running and crashes.
I debugged this problem, and somehow the application runs right past the Application.Exit call. I'm running in Debug mode, and this is relevant because of a small amount of code that depends on the RELEASE variable being defined. Here is my app exit code. I have traced the code and it entered the ExitApp method, and keeps on going, returning control to the caller and eventually crashing.
This is an application which provides reports over a remote desktop connection, so that's why the exit code is a bit weird. Its trying to terminate the remote session, but only when running under release because I don't want to shut down my dev machine for every test run.
private void ExitApp()
{
HardTerminalExit();
Application.Exit();
}
// When in Debug mode running on a development computer, this will not run to avoid shutting down the dev computer
// When in release mode the Remote Connection or other computer this is run on will be shut down.
[Conditional("RELEASE")]
private void HardTerminalExit()
{
WTSLogoffSession(WTS_CURRENT_SERVER_HANDLE, WTS_CURRENT_SESSION, false);
}
I've run a debugger right past the Application.Exit line and nothing happens, then control returns to the caller after I step past that line.
What's going on? This is a Windows Forms application.
This is an article which expands on the same train of thought you are going through: http://www.dev102.com/2008/06/24/how-do-you-exit-your-net-application/
Basically:
Environment.Exit - From MSDN: Terminates this process and gives the
underlying operating system the
specified exit code. This is the code
to call when you are using console
application.
Application.Exit - From MSDN: Informs all message pumps that they
must terminate, and then closes all
application windows after the messages
have been processed. This is the code
to use if you are have called
Application.Run (WinForms
applications), this method stops all
running message loops on all threads
and closes all windows of the
application. There are some more
issues about this method, read about
it in the MSDN page.
Another discussion of this: Link
This article points out a good tip:
You can determine if System.Windows.Forms.Application.Run has been called by checking the System.Windows.Forms.Application.MessageLoop property. If true, then Run has been called and you can assume that a WinForms application is executing as follows.
if (System.Windows.Forms.Application.MessageLoop)
{
// Use this since we are a WinForms app
System.Windows.Forms.Application.Exit();
}
else
{
// Use this since we are a console app
System.Environment.Exit(1);
}
Having had this problem recently (that Application.Exit was failing to correctly terminate message pumps for win-forms with Application.Run(new Form())), I discovered that if you are spawning new threads or starting background workers within the constructor, this will prevent Application.Exit from running.
Move all 'RunWorkerAsync' calls from the constructor to a form Load method:
public Form()
{
this.Worker.RunWorkerAsync();
}
Move to:
public void Form_Load(object sender, EventArgs e)
{
this.Worker.RunWorkerAsync();
}
Try Environment.Exit(exitCode).
I have went though this situation in many cases I use Thread.CurrentThread.Abort()
and the process is closed. It seems that Application.Exit isn't hooking up properly with current thread.
Also ensure any threads running in your application have the IsBackground property set to true. Non-background threads will easily block the application from exiting.
Make sure you have no Console.ReadLine(); in your app and Environment.Exit(1); will work and close your app.
I created the following that will exit the app anywhere. You don't have to worry if the Form is running or not, the test determines that and calls appropriate Exit.
public void exit(int exitCode)
{
if (System.Windows.Forms.Application.MessageLoop)
{
// Use this since we are a WinForms app
System.Windows.Forms.Application.Exit()
}
else
{
// Use this since we are a console app
System.Environment.Exit(exitCode);
}
} //* end exit()
Is this application run (in the Main method) using Application.Run()? Otherwise, Application.Exit() won't work.
If you wrote your own Main method and you want to stop the application, you can only stop by returning from the Main method (or killing the process).
Try this :
in Program.cs file :
after Application.Run(new form());
add Application.Exit();
private void frmLogin_FormClosing(object sender, FormClosingEventArgs e)
{
if (e.CloseReason == CloseReason.UserClosing)
{
DialogResult result = MessageBox.Show("Do you really want to exit?", "Dialog Title", MessageBoxButtons.YesNo);
if (result == DialogResult.Yes)
{
Environment.Exit(0);
}
else
{
e.Cancel = true;
}
}
else
{
e.Cancel = true;
}
}