cross threading seting form controls

Mickey Marshall

I found something very curious today:

I have a standard c# Windows Form type program that has a couple of threads in it.

One thread is the "Stop" thread. In it, when the work of the thread is complete I want to re-enable some form controls.

Originally, Stop was run in the main thread but for other reasons, I had to put into a separate thread. So the code was unchanged from the beginning. Then I realized that there was another control I had to enable.

I added 'tsbPlay.Enabled=true' and as expected I got a cross threading error when I got there.

Then I noticed that just above I noticed that I was calling 'this.buttonx.enabled' all along with no problems. So I change 'tsbPlay.Enabled=true' to 'this.tsbPlay.Enabled=true' and all worked error free.

Having successfully blown my mind I decided to ask the experts .

I'm sure that this method is probably not cool but why does it not work?

Thanks

Moose

P.S. I'm using VS2005.

4 Replies

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Mickey Marshall10y ago
Normally, that's what I do too. However, a ToolStripButton does not seem to support InvokeRequired not even Invoke. I will probably replace the ToolStrip with a group of buttons and handle it as normal. Thanks
Rajesh Singh10y ago
I have also faced this cross thread problem in windows application.
It works some times but some times doesnot work. Some where it works but some time doesn't.
It works for some controls but it doesnot work for some controls. It will not work when you have multiple thread like UI thread, file watcher, etc.
So I handle cross threading using InvokeRequired---

if (this.InvokeRequired)
{
this.Invoke((MethodInvoker)delegate
{
UpdateControl();// access UI controls
});
}
else
{
UpdateControl();//access UI controls
}
Mickey Marshall10y ago
Thank you for your reply but you missed the point:
It actually works without a cross thread error when I use 'this.control'.
Also, The 'Control' is actually a toolstripbutton and therefore has neither Invoke or InvokeRequired.

Moose
Rajesh Singh10y ago
Hi
UI runs in separate thread than other threads which you are using.
When you are using any UI control in your thread apart of UI thread then it will give cross thread error.

Please use below code to avoid cross threading issue.

if (this.InvokeRequired)
{
this.Invoke((MethodInvoker)delegate
{
UpdateControl();// access UI controls
});
}
else
{
UpdateControl();//access UI controls
}

http://stackoverflow.com/questions/5868783/solve-a-cross-threading-exception-in-winforms/