Illegal cross thread exception in Invoke method

Dave Kreskowiak

Without seeing your code, it's pretty much impossible to tell you where it's going wrong.

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yeah1000

Code is the following:

Delegate:
private delegate void ChangeTextDelegate(string text);

Method:
public static void ChangeText(string text)
{
if (richtextbox1.InvokeRequired)
{
richtextbox1.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
}
else
{
int startIndex;
startIndex = richtextbox1.TextLength; <- Exception points here
...
}
}

I call it like this: ChangeText("hello"); (in another thread)

modified on Thursday, March 18, 2010 7:19 AM

Luc Pattyn · modified on Thursday, March 18, 2010 7:19 AM

Hi, please show code inside PRE tags, that results in better readability. What you have shown seems correct, assuming the RTB got created on the GUI thread. It would be wrong when created e.g. inside the DoWork handler of a BackgroundWorker. How and where did you create it? :)

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

I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.

AspDotNetDev · modified on Thursday, March 18, 2010 7:19 AM

FYI, this is what code looks like when you wrap it in PRE tags and specify C# for the LANG attribute, as Luc mentioned:

// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
if (richtextbox1.InvokeRequired)
{
richtextbox1.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
}
else
{
int startIndex;
startIndex = richtextbox1.TextLength; // <- Exception points here.
// ...
}
}

Not sure why you are getting an exception there (perhaps post a screenshot and the full text of the exception?), but you might try the following to see if it works (changes in bold):

// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
if (this.InvokeRequired)
{
this.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
}
else
{
int startIndex;
startIndex = richtextbox1.TextLength; // <- Exception points here.
// ...
}
}

FYI, here is what I typed to make the code look like it does above:

<pre lang="C#">// Delegate:
private delegate void ChangeTextDelegate(string text);

// Method:
public static void ChangeText(string text)
{
if (<big><big>this</big></big>.InvokeRequired)
{
<big><big>this</big></big>.Invoke(new ChangeTextDelegate(ChangeText), new object[] { text });
}
else
{
int startIndex;
startIndex = richtextbox1.TextLength; // <- Exception points here.
// ...
}
}</pre>

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AspDotNetDev

FYI, that would prevent a locking situation, but would not likely prevent a cross-thread exception. It would also change the flow of the program (i.e., the call would be asynchronous rather than blocking), which the OP may not want.

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Luc Pattyn

I agree. :)

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

I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that.

yeah1000

Here is the stack trace, perhaps it can help clarify the problem...

System.InvalidOperationException was unhandled
Message="Cross-thread operation not valid: Control 'SomeClass' accessed from a thread other than the thread it was created on."
Source="System.Windows.Forms"
StackTrace:
at System.Windows.Forms.Control.get_Handle()
at System.Windows.Forms.Control.get_InternalHandle()
at System.Windows.Forms.Control.WmWindowPosChanged(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.TextBoxBase.WndProc(Message& m)
at System.Windows.Forms.RichTextBox.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.CallWindowProc(IntPtr wndProc, IntPtr hWnd, Int32 msg, IntPtr wParam, IntPtr lParam)
at System.Windows.Forms.NativeWindow.DefWndProc(Message& m)
at System.Windows.Forms.Control.DefWndProc(Message& m)
at System.Windows.Forms.Control.WmCreate(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.TextBoxBase.WndProc(Message& m)
at System.Windows.Forms.RichTextBox.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.IntCreateWindowEx(Int32 dwExStyle, String lpszClassName, String lpszWindowName, Int32 style, Int32 x, Int32 y, Int32 width, Int32 height, HandleRef hWndParent, HandleRef hMenu, HandleRef hInst, Object pvParam)
at System.Windows.Forms.UnsafeNativeMethods.CreateWindowEx(Int32 dwExStyle, String lpszClassName, String lpszWindowName, Int32 style, Int32 x, Int32 y, Int32 width, Int32 height, HandleRef hWndParent, HandleRef hMenu, HandleRef hInst, Object pvParam)
at System.Windows.Forms.NativeWindow.CreateHandle(CreateParams cp)
at System.Windows.Forms.Control.CreateHandle()
at System.Windows.Forms.TextBoxBase.CreateHandle()
at System.Windows.Forms.Control.get_Handle()
at System.Windows.Forms.Ric

yeah1000

Soo, any ideas? :)

AspDotNetDev

I assume you already tried using the "this" keyword like I said above? If that doesn't work, you can take two approaches. With one approach, try to create the error with a very small tester form. Then, post that here for us to review. Or, try removing code from your project little by little until it starts working.

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yeah1000

I am currently testing it with the 'this' keyword. But why should this approach solve the problem? What are the technicalities behind it? :)

AspDotNetDev

Was just a wild guess really. Not sure if it would help.

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yeah1000

Okay, that didn't help :( Any more ideas?

AspDotNetDev

Show me the exact code that causes the problem. Create as small of a tester application as you can and paste ALL of the code for it (but remember to try and make the example concise). It's probably something simple, but I can't help you unless I see the code you are using.

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yeah1000

I was finally able to fix the problem: Apparently the handle for the richtextbox did not exist when i tried to invoke it. Since i used it in a background thread, the invokerequired property returned 'false', sometimes causing it to display the illegal cross thread operation exception (suring program startup). The solution was to use the Form_load event which would signal the background thread when it was fully loaded. But its still a bit unclear how such a thing can happen. When does actually InitializeComponent return? When can i be sure that the control handles exist?

AspDotNetDev

Glad to hear you got it working. :) InitializeComponent should be called from the constructor. You should only reference controls after that call to InitializeComponent.

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yeah1000

Oh but i did call it from the constructor, then started the background thread and inside that thread tried to access the controls.