Cross-thread operation not valid: Control 'rchsdtOut' accessed from a thread other than the thread it was created on

Question

So I am getting this cross thread error and I cannot figure it out. Here is my base code before I attempted to muck around with it.

Bascally what the code is going is calling a batch file which then calls a java file. The outputdata is then redirected to the console in real time. When I just redirect the output just to the C# console, it works fine. But I want the same info to print out into a rich text box within the app. VS 2010 complaines at rchsdtOut.Text = e.Data.ToString(); that Cross-thread operation not valid: Control 'rchsdtOut' accessed from a thread other than the thread it was created on.

I have tried looking this up, and I do admit I am new to threading, so any help on how to easy accomplish this would be appreciated.

   //Declare and instantiate a new process component.
    System.Diagnostics.Process process1;
    process1 = new System.Diagnostics.Process();
    process1.StartInfo.UseShellExecute = false;
    process1.StartInfo.RedirectStandardOutput = true;
    process1.StartInfo.CreateNoWindow = true;
    process1.StartInfo.FileName = "cmd.exe";
    process1.StartInfo.Arguments = "BATFile.bat";
    process1.OutputDataReceived += (s, a) => myMethod(a);
    process1.Start();
    process1.BeginOutputReadLine(); 
    process1.WaitForExit();
    process1.Close(); 


    private void myMethod(DataReceivedEventArgs e) {       
       if (e.Data != null)
        {         
           rchsdtOut.Text = e.Data.ToString();
           Console.WriteLine(e.Data.ToString());

        } 
    }//end of private

Chris Shain · Answer 1 · 2012-01-19T18:35:08.237

6

Try this line:

process1.OutputDataReceived += (s, a) => rchsdtOut.Invoke(new System.Action(()=> myMethod(a)));

edited Jan 19 '12 at 18:35

answered Jan 19 '12 at 17:31

Chris Shain

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I added that line, but vs2010 indicates that cannot convert lambda expression type 'system.delegate' becuase it's not a delegate type. – user1158745 Jan 19 '12 at 18:13

score 5 · Accepted Answer · answered Jan 19 '12 at 17:32

5

It's not legal to access a WinForms control from a thread other than the one it was created on. You need to use Invoke or BeginInvoke to get control back to the appropriate thread.

private void myMethod(DataReceivedEventArgs e) {       
  if (e.Data != null) {
    Action action = () => rchstdOut.Text = e.Data.ToString();
    rchstdOut.Invoke(action, null);
    Console.WriteLine(e.Data.ToString());
  }
}

answered Jan 19 '12 at 17:32

JaredPar

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+1 This is a better solution than mine, because it waits to marshal until it is sure that the payload isn't null. – Chris Shain Jan 19 '12 at 17:39
@user1158745 that's really odd. Try using BeginInvoke instead of Invoke – JaredPar Jan 19 '12 at 18:23
Well the app doesn't appear to hang, but nothing is logged. – user1158745 Jan 19 '12 at 19:52
@user1158745 that likely means you aren't pumping your UI thread to let messages through. The problem appears to be the call to `WaitForExit`. That will block the UI thread and messages until the app completes. Try removing that call and it should start working as expected – JaredPar Jan 19 '12 at 19:53
Worked like a charm. Only issue, it doesn't seem to be appending to the richtextbox, but just overwriting it. anyideas? – user1158745 Jan 19 '12 at 20:08
This seemed to do is Action action = () => rchsdtOut.Text += "\r\n" + e.Data.ToString(); Thanks for your help. – user1158745 Jan 19 '12 at 20:10

Strillo · Answer 3 · 2012-01-20T08:37:32.947

0

Well rchsdtOut can only be upodated from the UI thread while your method is called from another. There are several solutions. If you want to have a general method to update controls you can check the control.InvokeRequired property (or this.Dispatcher.CheckAccess() in WPF) and use a delegate.

    private delegate void UpdateTextControlDelegate(Control control, string text);

    private void UpdateTextControl(Control control, string text)
    {
        if (control.InvokeRequired)
        {
            Invoke(new UpdateTextControlDelegate(UpdateTextControl), new object[] { control, text});
            return;
        }

        control.Text = text;
    }

...

if (e.Data != null)
{         
     UpdateTextControl(rchsdtOut, e.Data.ToString());
     Console.WriteLine(e.Data.ToString());
}

edited Jan 20 '12 at 08:37

answered Jan 19 '12 at 17:34

Strillo

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No need for checking here- the OP is explicitly starting a thread, so we *know* an Invoke is needed. – Chris Shain Jan 19 '12 at 17:40
1

True, however this way you can reuse the function in case you need it to be called not JUST by the OutputDataReceived event. – Strillo Jan 19 '12 at 17:46
I wanted to give this method a try, howerver, vs2010 doesn't like the 2nd new[]. Indicates no best type found for implicitly-typed array. – user1158745 Jan 19 '12 at 18:21
You can just use 'new object[]'. – Strillo Jan 19 '12 at 19:40
I gave that a try, but nothing is being written to the richtext box. – user1158745 Jan 19 '12 at 19:56
What is the value of `e.Data`? – Strillo Jan 20 '12 at 08:37

score 0 · Answer 4 · edited May 23 '17 at 10:34

0

You cannot access a Form Control from a thread other then where it was created. You will need to create some other object that both of the threads can access. Producer Consumer Problem

edited May 23 '17 at 10:34

Community

1
1

answered Jan 19 '12 at 17:36

Ryan Taylor

71
5

Cross-thread operation not valid: Control 'rchsdtOut' accessed from a thread other than the thread it was created on

4 Answers4