Illegal cross thread exception in Invoke method

[AspDotNetDev]

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 (<b><big><big><u>this</u></big></big></b>.InvokeRequired)
{
<b><big><big><u>this</u></big></big></b>.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.

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[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.