CODEWITHSUNDEEP
c#wpfmultithreading
Sangeetha
Sangeetha

Reputation: 709

Calling thread cannot access this object

In my wpf application I have added a piece of code in the button click as below:

 private void btn_convert_Click(object sender, RoutedEventArgs e)
 {
    Thread t = new Thread(new ThreadStart(WorkerMethod));
    t.SetApartmentState(ApartmentState.MTA);
    t.IsBackground = true;
    t.Start();
 }

Inside my WorkerMethod() method I have some code like the line below:

btn_convert.Content = "Convert";

When it reaches to this line it throws the exception as the calling thread cannot access this object because a different thread owns it.

I dont want to use Dispatcher as it freezes the UI.. UI should be responsive so I have not opted for Dispatcher invoke or BeginInvoke.

Please give me your valuable suggestions.

Upvotes: 0

Views: 197

Answers (2)

DerApe
DerApe

Reputation: 3175

UI changes can only be applied by the main thread. You can check if the main thread call is necessary:

if (btn_convert.InvokeRequired)
{
  btn_convert.Invoke((MethodInvoker)(() => btn_convert.Content = "Convert"));
}

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1503290

I dont want to use Dispatcher as it freezes the UI.. UI should be responsive so i am not opted for Dispatcher invoke or BrginInvoke.

That just shows that you've used the dispatcher badly.

You must access the UI from the UI thread. That doesn't mean your whole WorkerMethod needs to run on the UI thread, but this line:

btn_convert.Content = "Convert";

definitely does. So you might want to keep your current code for starting a thread (do you really need to set the apartment state though) but change any code accessing the UI to use the dispatcher. For example:

Action setButtonContentAction = () => btn_convert.Content = "Convert";
Dispatcher.BeginInvoke(setButtonContentAction);

Alternatively, depending on what your WorkerThread is doing - and if you're using C# 5 - you might want to use the new async features. That can make it easier to keep UI work on the UI thread, but it does depend on what else is going on.

Upvotes: 7

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