In C#, wait on the mainthread while continuing to process UI updates? (.NET 2.0 CF)

Question

I want to otherwise block code execution on the main thread while still allowing UI changes to be displayed.

I tried to come up with a simplified example version of

Answer 1

You should probably restructure your code as others have suggested, but depending on the behavior you're looking for, you might also want to have a look at using a Thread.Join on your background worker thread. Join actually allows the calling thread to process COM and SendMessage events while it waits for the other thread to finish. This seems like it could be dangerous in come cases, but I've actually had a couple scenarios where it was the only way to wait for another thread to finish cleanly.

Thread..::.Join Method

Blocks the calling thread until a thread terminates, while continuing to perform standard COM and SendMessage pumping.

(from http://msdn.microsoft.com/en-us/library/95hbf2ta.aspx)

Answer 2

I agree with the others that are suggesting you use Background Worker. It does the heavy lifting and allows the UI to continue. You can use the Report Progress of Background Worker to initiate times where the Main Form can be set to be disabled while it performs the actions in the background and then re-enable once the 'certain instances' have completed processing.

Let me know if this helps! JFV

Answer 3

Just a code snippet: don't have much time sorry :)

    private void StartMyDoSomethingThread() {
        Thread d = new Thread(new ThreadStart(DoSomething));
        d.Start();
    }

    private void DoSomething() {
        Thread.Sleep(1000);
        ReportBack("I'm still working");
        Thread.Sleep(1000);
        ReportBack("I'm done");
    }

    private void ReportBack(string p) {
        if (this.InvokeRequired) {
            this.Invoke(new Action<string>(ReportBack), new object[] { p });
            return;
        }
        this.Text = p;
    }

Answer 4

Common activities which 'block' the main thread are things like opening messages boxes or modal dialog. The main code appears to block at the MessageBox or ShowDialog call.

The way those items work (and MessageBox is just a specialized modal dialog) is that they contain their own message pump while they're blocking.

Although it's a nasty hack, you can do something like this in your app by looping calling Application.DoEvents() to keep the user messages pumping while you're waiting for your other task to complete. You need to be careful because all sorts of nasty things might lead from pumping messages like this - for example someone close the form or reenter your current message handler - the modal dialogs avoid this by effectively disabling input from the form which launches them.

I did mean to say that BackgroundWorker is a better solution, if you can make it fit. I sometimes combine it with a modal 'progress dialog' to give me the background thread / message pumping and the blocking of the UI thread.

Edit - to expand on the last bit:

One approach I've used is to have a 'progress form' class, which takes a BackgroundWorker object as a constructor parameter, and contains handlers for the progress and completion events of the background worker which gets passed to it.

The form which wants the work done creates the background worker and hooks up the 'work' event (can't remember what it's called right now), and then creates a progress dialog to which it passes the background worker. It then modally shows the progress dialog, which means it will wait (but pumping messages) until the progress dialog closes.

The progress form is responsible for starting the BackgroundWorker from its OnLoad override, and closes itself when it sees the BackgroundWorker complete. Obviously you can add message text, progress bars, cancel buttons, whatever to the progress form.