C# invalid cross thread call while invoking?!

Question

5.00/5 (1 vote)

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Hello!

I use the following method to invoke something:

C#

public void InvokeHelper(object from, object to)
        {
            BeginInvoke(new MethodInvoker(delegate()
            {
                from = to;
            }));
        }

But sometimes it throws an invalidcrossthreadcall exception. I use it about 50 times a second.

So the question is why is it throw exception?

Posted 14-Jan-11 4:24am

velvet7

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Comments

#realJSOP 14-Jan-11 10:29am

What happens if you call it less frequently?

velvet7 14-Jan-11 10:33am

Well, maybe if i call it less frequently solves the problem, but I have to call it 50 times a seco

#realJSOP 14-Jan-11 10:39am

Were the from and to objects created on the UI thread, or in the thread that's calling the InvokeHelper method?

Nish Nishant 14-Jan-11 10:51am

Post more info such as whether this is Silverlight, Winforms, WPF etc.

Sergey Alexandrovich Kryukov 14-Jan-11 10:58am

@velvet7: of course not, this is a bug! Normally, Invoke always work, but this is not real Invoke.
Please 1) show the code of MethodInvoker; 2) Is it WinForms? 3) If your code, BeginInvoke if the method of what instance of what class (in other words, in what class you write this InvokeHelper method?

The problem is way too easy to resolve if you answer these questions.

velvet7 14-Jan-11 11:03am

1) MethodInvoker is in .Net, that isn't mine 2) Yes, it is in WinForms 3) I write it in Form1 : Form class

velvet7 14-Jan-11 11:10am

The full exception:Cross-thread operation not valid: Control 'Form1' accessed from a thread other than the thread it was created on.

Maybe it helps.

_Erik_ 14-Jan-11 12:00pm

Is this exactly the code your program runs or have you simplified it? I'm asking becouse, for example, calling CreateGraphics on a control which has not still created the handle can cause illegal cross thread calls.

velvet7 14-Jan-11 14:12pm

Yes. But I still can't get it to work.

4 solutions

Solution 3

you might want to consider the context as well

C#

public void InvokeHelper(object from, object to, System.Threading.SynchronizationContext context)
        {

              _conex.Post(new SendOrPostCallback((obj) => {
                                                     
                     //your code here
                     }
              ), null);

        }

Posted 14-Jan-11 6:37am

cechode

Solution 4

Consider to use ThreadSynchronization pattern.
As a remember BeginInvoke returns asyncResult
So, you can use AsyncWaitHandle.WaitOne

Posted 14-Jan-11 21:52pm

Lionberg

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Espen Harlinn · Accepted Answer · 2011-01-14T05:59:00

Solution 1

Try writing it like this:

public void InvokeHelper(object from, object to)
{
 BeginInvoke( (MethodInvoker) delegate { from = to; });
}

Regards
Espen Harlinn

Posted 14-Jan-11 5:59am

Espen Harlinn

E.F. Nijboer · Accepted Answer · 2011-01-14T06:04:00

I would suggest to first check if it is necessary. You might also need to check IsHandleCreated to ensure that the control is created. Have a look at the first link for more info on that and for an example check the second link.

if(this.InvokeRequired)
{
  this.BeginInvoke(method);
} else
{
  method();
}

http://msdn.microsoft.com/nl-nl/library/system.windows.forms.control.invokerequired.aspx[^]

http://msdn.microsoft.com/nl-nl/library/ms171728.aspx[^]

Good luck!