MultiThreaded apps and Getting values?

[knowthediff]

Hello,
I have a VS2003 app that I moved to VS 2005. I am trying to correct
the error that I now receive when the app runs. In several places I am
getting a InvalidOperationException "Cross-thread operation not valid:
Control '' accessed from a thread other than the thread it was created
on." I have been reading alot about this and I understand why I am
getting the error, but I am having problems fixing the problem.

Basically I have a custom control that inherits from a RichTextBox. In
vs 2003 something like this code:
this.SelectionStart = int.MaxValue;

Translates to this in vs2005:

delegate void SetSelectionStartCallback(int value);

private void SetSelectionStart(int value)
{
if (this.InvokeRequired)
{
SetSelectionStartCallback d = new
SetSelectionStartCallback(SetSelectionStart);
this.Invoke(d, new object[] { value });
}
else
{
this.SelectionStart = value;
}
}

this.SetSelectionStart(int.MaxValue);

This part I am OK with, but for simple "get" calls to the base
RichTextBox's properties I do not know how to code these. For example,
this next line of code throws the same error. How do I go about
retrieving the Text property in a thread safe manner? Is it possible
to retreive the instance to the control itself "this" in a thread safe
manner?

if (this.Text.Length > 0)

I do not want to take the easy way out and set
CheckForIllegalCrossThreadCalls=false.

Thanks!
-J

 

[Willy Denoyette [MVP]]

| Hello,
| I have a VS2003 app that I moved to VS 2005. I am trying to correct
| the error that I now receive when the app runs. In several places I am
| getting a InvalidOperationException "Cross-thread operation not valid:
| Control '' accessed from a thread other than the thread it was created
| on." I have been reading alot about this and I understand why I am
| getting the error, but I am having problems fixing the problem.
|
| Basically I have a custom control that inherits from a RichTextBox. In
| vs 2003 something like this code:
| this.SelectionStart = int.MaxValue;
|
| Translates to this in vs2005:
|
| delegate void SetSelectionStartCallback(int value);
|
| private void SetSelectionStart(int value)
| {
| if (this.InvokeRequired)
| {
| SetSelectionStartCallback d = new
| SetSelectionStartCallback(SetSelectionStart);
| this.Invoke(d, new object[] { value });
| }
| else
| {
| this.SelectionStart = value;
| }
| }
|
| this.SetSelectionStart(int.MaxValue);
|
| This part I am OK with, but for simple "get" calls to the base
| RichTextBox's properties I do not know how to code these. For example,
| this next line of code throws the same error. How do I go about
| retrieving the Text property in a thread safe manner? Is it possible
| to retreive the instance to the control itself "this" in a thread safe
| manner?
|
| if (this.Text.Length > 0)
|
| I do not want to take the easy way out and set
| CheckForIllegalCrossThreadCalls=false.
|
| Thanks!
| -J
|

One option is to use the MethodInvoker...

Invoke(new MethodInvoker(delegate() {
if (this.Text.Length > 0)
....
}),null);


Willy.