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Cross Thread

By , 23 Oct 2006
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Sample Image - Cross_Thread.jpg

Introduction

We can't perform operation on a control, if that control was created by another thread. While doing this kind of operations, we get Cross Thread is not valid. like that.

About this code

In this sample, i have used only one text box. I am planning to display GUID in textbox with uncondition loop. If we do that without thread, the application will be hang. so, I have created a thread in form load event.
private void Form1_Load(object sender, EventArgs e)
{
       guidThread = new Thread(new ThreadStart(CreateNewGuid));
       guidThread.Start();
}

Thread Method

There is a method CreateNewGuid() to generate guid with unconditional loop. Here, invoking a delegate event GuidThreadCallBack() to assgin the new generated guid to text box.
 public delegate void GuidThreadCallBack();
while (true)
  {
    newGUID = Guid.NewGuid().ToString();
    try
    {
     this.Invoke(new GuidThreadCallBack(setTextBoxValue));
    }
    catch { guidThread.Abort(); }
  }

Delegate Event Method

This method will assign the value to the text box. While assging the value to textbox, the delegate event method will use which thread created the text box.
private void setTextBoxValue()
 {
   textBox1.Text = newGUID;
   textBox1.Refresh();
 }

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

raajaak
Software Developer General Physics Corporation (GP)
India India
No Biography provided

Comments and Discussions

 
GeneralWatiN problem on Vista PinmemberKvita Patil30-Jul-09 1:11 
GeneralGot cross thread operation exception PinmemberKvita Patil3-Jul-09 23:55 
Generalanother way ... PinmemberAntofagasta20-Jun-08 8:09 
This is a very short snippet that demonstrates how to deal with cross-threading (for example using text boxes and other controls) in a nice manner. Note, however, not all controls can behandled in this manner. This approach might be useful in changing various control properties like the TEXT, COLOR, VALUE, ... from a different thread.
 
public class TextBoxCallbacks
{
delegate void SetTextBoxTextColor_Callback(TextBox txtbox, Color clr);

public static void SetTextBoxTextColor(TextBox txtbox, Color clr)
{
if (txtbox != null)
{
if (txtbox.InvokeRequired)
{
SetTextBoxTextColor_Callback d =
new SetTextBoxTextColor_Callback(SetTextBoxTextColor);
txtbox.Invoke(d, new object[] { txtbox, clr });
}
else
{
if (clr != null)
{
txtbox.ForeColor = clr;
}
else
throw new Exception("TextBoxColorException!");
}
}
else
throw new Exception("TextBoxEmptyException !");
}
....
other delegates and associated methods
....
}
GeneralCross Thread not valid in Form Pinmemberanu91417-Mar-08 18:24 
Questionwhat about BackgroundWorker? Pinmembereligazit24-Oct-06 12:03 

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