I have a winform application (one form), on this form there is a RichTextBox. In the constructor of this form I create an instance of the class MyClass
. In the
Using BackgroundWorker component, only the ProgressChanged
and RunWorkerCompleted
events allow you to invoke methods/properties on UI controls (which should be always done on UI thread). As you are updating the UI in DoWork
event which runs on a non-UI thread you are getting this error, you should probably update you UI controls using Invoke or BeginInvoke methods in DoWork event if you want to.
i think the error stops on this line:
richtextBox.Text.Add("MyText");
your question i similar to this:
BackgroundWorker OnWorkCompleted throws cross-thread exception
Add:
e.Result = "MyText";
In your bw_DoWork
And:
richTextBox1.AppendText((string)e.Result);
In your bw_RunWorkerCompleted
(Alter it to fit your code)
EDIT:
If it's done many times during the BackgroundWorker
's work, you can add:
_bw.ReportProgress(0, "MyText");
to the bw_DoWork
and:
richTextBox1.AppendText((string)e.UserState);
to the bw_ProgressChanged
.
To make it cleaner and based on Jon Skeet's suggestion, I made an extension method which does the same, you can change the "this Label control
" to this TextBox control
or simply use "this Control control
" (and basically allow every control to be updated easily):
internal static class ExtensionMethods
{
/// <summary>
/// Updates the label text while being used in a multithread app.
/// </summary>
/// <param name="control">The control.</param>
/// <param name="text">The text.</param>
internal static void UpdateThreadedText(this Label control, string text)
{
Action action = () => control.Text = text;
control.Invoke(action);
}
/// <summary>
/// Refreshes the threaded.
/// </summary>
/// <param name="control">The control.</param>
internal static void RefreshThreaded(this Label control)
{
Action action = control.Refresh;
control.Invoke(action);
}
}
And then the usage is quite simple:
this.yourLabelName.UpdateThreadedText("This is the text");
this.yourTextBoxName.UpdateThreadedText("This is the text");
this.yourControlName.UpdateThreadedText("This is the text");
or
this.yourLabelName.RefreshThreaded();
Works for me nicely :)
Using BackgroundWorker
doesn't exempt you of the normal threading rules - such as that only the UI thread can access UI components.
If you want to update the UI from a BackgroundWorker
other than using the progress/completion events (which are raised on the UI thread) you need to use Control.Invoke / Control.BeginInvoke just as you would in other situations. For example:
if (....)
{
Action action = () => richtextBox.Text.Add("MyText");
richtextBox.Invoke(action); // Or use BeginInvoke
}
try this code,
BeginInvoke((MethodInvoker)delegate
{
richtextBox.Text.Add("MyText");
});