How to change window state of Form, on a different thread?

Question

Does anyone know how I can change the window state of a form, from another thread? This is the code I'm using:

    private void button4_Click(object sender, EventArgs e)
    {
            string pathe = label1.Text;
            string name = Path.GetFileName(pathe);
            pathe = pathe.Replace(name, "");
            string runpath = label2.Text;
            Process process;
            process = new Process();

            process.EnableRaisingEvents = true;
            process.Exited += new System.EventHandler(process_Exited);

            process.StartInfo.FileName = @runpath;
            process.StartInfo.WorkingDirectory = @pathe;
            process.Start();
            WindowState = FormWindowState.Minimized;
    }
    private void process_Exited(object sender, EventArgs e)
    {
        this.WindowState = FormWindowState.Normal;
    }

It's meant to run a program and minimize, then return to the normal state once the program has closed. Although I get this error "Cross-thread operation not valid: Control 'Form1' accessed from a thread other than the thread it was created on." Any idea how to get this to work?

score 9 · Accepted Answer · answered Apr 08 '10 at 15:31

9

This will work in .NET 3.5:

Invoke(new Action(() => { this.WindowState = FormWindowState.Normal; }));

Or 2.0:

Invoke(new MethodInvoker(delegate { this.WindowState = FormWindowState.Normal; }));

answered Apr 08 '10 at 15:31

Adam Robinson

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In 2.0 you can just go `Invoke(new Action(delegate { this.WindowState = FormWindowState.Normal; }));` as well, not MethodInvoker if you don't want to. Action exists in 2.0, it's Func<> that doesn't. – Kevin Anderson Apr 08 '10 at 16:13
@Kevin: True, but Action (no ``) only exists in 3.5 – Adam Robinson Apr 08 '10 at 16:29
That's true, with no type it's 3.5. – Kevin Anderson Apr 08 '10 at 17:38

score 1 · Answer 2 · answered Apr 08 '10 at 15:29

1

Just search this string in StackOverflow "Cross-thread operation not valid" or Google. Please, don't be that lazy.

answered Apr 08 '10 at 15:29

Andrey

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score 1 · Answer 3 · edited May 23 '17 at 10:30

1

See What’s the difference between Invoke() and BeginInvoke() on this site. The "chosen" answer gives a good explanation of what you're supposed to do.

Long story short, you want different THREADS not making a new process entirely (or highly unlikely you want that), and you probably want to use Invoke() and not BeginInvoke() which is asynchronous.

edited May 23 '17 at 10:30

Community

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answered Apr 08 '10 at 15:31

Kevin Anderson

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@Kevin: Considering he's starting an external application and waiting for it to exit, it seems like another process is *exactly* what he wants (in fact, requires). – Adam Robinson Apr 08 '10 at 16:35

score 1 · Answer 4 · answered Apr 08 '10 at 15:32

1

Add this line of code to the Click event handler:

process.SynchronizingObject = this;

answered Apr 08 '10 at 15:32

Hans Passant

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score -2 · Answer 5 · edited Sep 10 '13 at 21:10

-2

this will solve your problem add it in the form_load event

 System.Windows.Forms.Control.CheckForIllegalCrossThreadCalls = false;

edited Sep 10 '13 at 21:10

Roman C

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answered Sep 10 '13 at 20:48

hossein nazari

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This doesn't fix the problem, it *hides* the problem, by introducing race conditions into your code resulting in unexpected, unexplained, and inconsistent errors when running the code. As the program becomes more complex, the likelihood of problems, and the difficulty in either tracking them down or fixing the underlying problems, rises very quickly. This exception being thrown is a *feature*, and one that is very valuable. Disabling it is something you should virtually never be doing. – Servy Sep 10 '13 at 20:52

How to change window state of Form, on a different thread?

5 Answers5