Check For Illegal Crossthreads Error

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How does one correct this?

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

Posted 1-May-11 7:00am

Member 7766180

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Sergey Alexandrovich Kryukov 1-May-11 15:47pm

Tag it! WPF, Forms, what?!
--SA

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Kim Togo · Accepted Answer · 2011-05-01T07:13:00

Solution 1

Check out Control.InvokeRequired[^] from MSDN.

Basic you do:

private void DisplayString(string index)
{
  if (this.InvokeRequired)
  {
    this.Invoke(new Action(() => DisplayString(index)));
    return;
  }
  this.textBox_Index.Text = index;
}

InvokeRequired tells if the caller is from another thread then where the TextBox was created. If it is true.
We have to Invoke to the same thread before we can change the TextBox.

WinForms UI Thread Invokes: An In-Depth Review of Invoke/BeginInvoke/InvokeRequre[^]

Posted 1-May-11 7:13am

Kim Togo

Updated 1-May-11 7:29am

v2

Comments

Member 7766180 1-May-11 14:12pm

Thank You Kim!
DS

Kim Togo 1-May-11 15:03pm

Your are welcome.

Sergey Alexandrovich Kryukov 1-May-11 15:49pm

Yes, that's it, my 5. Well, InvokeRequred is rarely needed, as developers often know it's not UI thread. Dispatcher would be better as OP did not specify Forms or WPF or what.
--SA

Kim Togo 2-May-11 2:29am

Thanks SA. You a right about InvokeRequred is rarely needed.
But if you what to make a method "Thread-safe" in a UI control. InvokeRequred is a good thing.

Sergey Alexandrovich Kryukov 2-May-11 3:58am

No! It would be just a waste of time. Not a mistake of course, but calling Invoke/BeginInvoke is not a mistake as well, so let's consider the perfect solution.

InvokeRequired will always return false if called from UI thread, always true otherwise.
Invoke will work in both cases.

Therefore, InvokeRequired should be used only in the method which can be called from both UI and non-UI thread; in all other cases it should be always Invoke/BeginInvoke (non-UI thread) or a direct call (UI thread). I considered all three cases -- final answer.

--SA