C# Can't close form created by Background Worker

Question

My Backgroundworker loads a new "pop-up" form, but how do I terminate background worker and the newly created form?

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    BussyForm bussyForm = new BussyForm();
    bussyForm.ShowDialog();
}

This has no effect:

backgroundWorker1.Dispose();
backgroundWorker1.CancelAsync();
backgroundWorker1 = null;

Info [here](http://stackoverflow.com/questions/4387527/how-to-properly-handle-form-closing-when-using-background-workers) and [here](http://stackoverflow.com/questions/16770337/closing-the-form-when-backgroundworker-stops-working). — Brian, Dec 10 '13 at 16:54

score 2 · Accepted Answer · answered Dec 10 '13 at 17:32

You shouldn't be showing a form from a non-UI thread. You should only have one UI thread, and it, and only it, should access all of your user interface controls. Your non-UI threads shouldn't access UI elements at all.

You should be showing the given busy popup from the UI thread instead.

Requesting cancellation from the BackgroundWorker, or disposing of it, won't close the form, or force the thread to stop executing, which is why your form stays open.

Instead just show your popup from the UI thread when you start the background worker, and have the BGW's completed event call Close on the form:

private void button1_Click(object sender, EventArgs args)
{
    BusyForm busyForm = new BusyForm();

    BackgroundWorker worker = new BackgroundWorker();
    worker.DoWork += worker_DoWork;
    worker.RunWorkerCompleted += (_, e) => { busyForm.Close(); };
    worker.RunWorkerAsync();

    busyForm.ShowDialog();
}

Ok.. I understand. I need to rethink my design. Thanks for the code! — Half_Baked, Dec 10 '13 at 22:04

score 0 · Answer 2 · answered Dec 10 '13 at 16:57

0

CancelAsync doesn't actually abort your thread or anything like that. It sends a message to the worker thread that work should be cancelled via BackgroundWorker.CancellationPending. Your DoWork delegate that is being ran in the background must periodically check this property and handle the cancellation itself.

You call bussyForm.ShowDialog(); so you need to close this form manually.

answered Dec 10 '13 at 16:57

Ringo

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Did you try backgroundWorker1.CancellationPending? – Ringo Dec 10 '13 at 17:10
Problem was i had two UI threads, so Im back to one, and now it works – Half_Baked Dec 10 '13 at 22:15

C# Can't close form created by Background Worker

2 Answers2

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