Is CancelAsync working or not?

Question

I've made a small app where Form is threaded (using BackgroundWorker), and in the form I'm calling a function QuitApplication in Program class when I want to quit.

The DoWork looks like this:

static void guiThread_DoWork(object sender, DoWorkEventArgs e)
{
    BackgroundWorker worker = sender as BackgroundWorker;

    while (true)
    {
        if (worker.CancellationPending == true)
        {
            e.Cancel = true;
            break;
        }

        if (Program.instance.form != null)
        {
            Program.instance.form.UpdateStatus(Program.instance.statusText, Program.instance.statusProgress);
        }

        Thread.Sleep(GUI_THREAD_UPDATE_TIME);
    }
}

and in the Form1 class i have this method attached to the closing of the window:

void Form1_FormClosed(object sender, FormClosedEventArgs e)
{
    Program.instance.SetStatus("Closing down...", 0);

    Program.QuitApplication();
}

So what i want is to ensure that everything quits when I press the X on the window. However, the if( worker.CancellationPending == true ) never hits... why is this?

QuitApplication looks like this:

public static void QuitApplication()
{
    Program.instance.guiThread.CancelAsync();

    Application.Exit();
}

And Im using guiThread.WorkerSupportsCancellation = true

possible duplicate of [.NET: How to wait for a BackgroundWorker to cancel?](http://stackoverflow.com/questions/123661/net-how-to-wait-for-a-backgroundworker-to-cancel) — codingbadger, Apr 18 '11 at 12:40

Christian Hayter · Accepted Answer · 2011-04-18T12:48:34.157

3

CancelAsync is setting the CancellationPending property, but then you immediately quit the application without giving the background thread a chance to detect that and shut down. You need to change your UI code to wait for the background thread to finish.

Personally, when I write apps like this, I make the form close button act like a Cancel button rather than quit immediately. It's a lot safer for the end user. For example:

private void abortButton_Click(object sender, EventArgs e) {
    // I would normally prompt the user here for safety.
    worker.CancelAsync();
}

private void Form1_FormClosing(object sender, FormClosingEventArgs e) {
    if(worker.IsBusy) {
        // If we are still processing, it's not very friendly to suddenly abort without warning.
        // Convert it into a polite request instead.
        abortButton.PerformClick();
        e.Cancel = true;
    }
}

edited Apr 18 '11 at 12:48

answered Apr 18 '11 at 12:39

Christian Hayter

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could I in QuitApplication do a while( guiThread.isBusy); before Application.Exit? BUT, dows Application.Exit terminate ALL? – Jason94 Apr 18 '11 at 12:45
Jason, have a look at Barry's question link for the answer to that. All I am saying is, I think it's more user-friendly to avoid the issue entirely by doing what I suggest instead. – Christian Hayter Apr 18 '11 at 12:49
How do you let the Form1 know about the worker? or did you mean: if( Program.instance.worker.IsBusy)? – Jason94 Apr 18 '11 at 13:13
Yes that's correct for your code. `BackgroundWorker` is normally intended to be used within a form, so that's how I constructed my example code. – Christian Hayter Apr 18 '11 at 13:44

Is CancelAsync working or not?

1 Answers1