How come another thread can update main controls without invoking them? [modified]

[yeah1000]

Hi, i have a strange problem. I can update any main thread control from a different thread without any cross thread exceptions. I can change the text of a textbox from the thread and from any button click handler in main thread. What are the possible causes of this kind of behavior? Can it somehow remember that i have used invoke on the controls? When i do the exact same thing in a new project i get the crossthread exception. An illustration of what i mean: private void button1_Click(object sender, EventArgs e) { Thread someThread = new Thread(Threadfun); someThread.Start(); } private void Threadfun() { label1.Text = "hello"; } ty

modified on Thursday, February 25, 2010 10:50 AM

[Saksida Bojan]

Are you compiled it under .NET framework? I know that in .NET2.0 was added detection.

[Lost User]

private void Form1_Load(object sender, EventArgs e)
{
Thread t = new Thread(RunMyThread);
t.IsBackground = true;
t.Start();
}

private void RunMyThread()
{
Invoke(new MethodInvoker(InvokeLabel));
}

private void InvokeLabel()
{
label1.Text = "Hello World";
}

[yeah1000]

.Net framework 3.5 stancrm, i know that this is the way to go but my problem was that i was able to chagne the parameter without invoking :)

[Saksida Bojan]

The only whay that it doesn't throw you is that you either used try catch to handle error or that control is created on a same thread as thread that is modifying your control. You can check AnyControl.InvokeRequired proprty

[Luc Pattyn]

some Control operations are harmless and work across threads without causing an exception; example: reading Label.Text. As this is undocumented, you should not rely on it. I collected the most relevant information here[^]. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

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I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.
All Toronto weekends should be extremely wet until we get it automated in regular forums, not just QA.

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[Rob Philpott]

There is a setting you could check: http://msdn.microsoft.com/en-us/library/system.windows.forms.control.checkforillegalcrossthreadcalls.aspx Interesting, according to that page exceptions are only thrown if debugging (which I hadn't realised). Are you debugging?

Regards, Rob Philpott.

[Luc Pattyn]

Rob Philpott wrote:

exceptions are only thrown if debugging

Didn't know that and so I checked it with a Threading.Timer modifying a Label.Text; throws an exception inside Visual Studio; however even a debug build will not throw an exception if run outside Visual Studio. :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]

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I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.
All Toronto weekends should be extremely wet until we get it automated in regular forums, not just QA.

---