Thread error in WPF (a different thread owns it.)

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1.00/5 (1 vote)

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Hi,

I am trying to access the textbox from another class in WPF. The method has been initiated by a thread. And when I am trying to set the textbox value it is getting an error

An unhandled exception of type 'System.InvalidOperationException' occurred in WindowsBase.dll

Additional information: The calling thread cannot access this object because a different thread owns it.

method called:

C#

Thread tScan = new Thread(MyClass.Start);

method Statusprint called from MyClass.Start() method like,

C#

public static void StatusPrint()
        {
            Instance.txtReport.Text = "value will set here.";
        }

As I am new in WPF so, need your help to get rid of this.

What I have tried:

I tried to do this way.

C#

public static void StatusPrint()
        {
            System.Windows.Threading.Dispatcher.CurrentDispatcher.BeginInvoke(new ThreadStart(() => Instance.txtReport.Text = "value will set here."));
        }

here Instance is a static variable declared in MainWindow class initiated to this.
here I am not getting any runtime error but it is just not executing.

Posted 1-Mar-17 0:57am

Arkadeep De

Updated 1-Mar-17 1:31am

v2

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Graeme_Grant · Answer 1 · 2017-03-01T01:03:00

Solution 1

Why ThreadStart inside the Dispatcher.CurrentDispatcher? You don't want to start a new thread. Change ThreadStart to Action and it should work.

Posted 1-Mar-17 1:03am

Graeme_Grant

Comments

Arkadeep De 1-Mar-17 7:40am

tried this one with Action. But getting this error..

{System.Windows.Threading.DispatcherOperation}
Dispatcher: {System.Windows.Threading.Dispatcher}
Priority: Normal
Result: null
Status: Pending
Task: Id = 85, Status = WaitingForActivation, Method = "{null}", Result = "{Not yet computed}"

Pete O'Hanlon 1-Mar-17 7:40am

My 5.

Pete O'Hanlon · Answer 2 · 2017-03-01T01:31:00

Solution 2

I have an extension method that I like to use in this case:

C#

public static void BeginInvokeIfRequired(this Dispatcher dispatcher, Action operation)
{
  if (operation== null) return;
  if (dispatcher.CheckAccess())
  {
    action();
  }
  else
  {
    dispatcher.BeginInvoke(action);
  }
}

To call it, all you need to do is this:

C#

Application.Current.Dispatcher.BeginInvokeIfRequired(()=>Instance.txtReport.Text = "value will set here.");

Posted 1-Mar-17 1:31am

Pete O'Hanlon

Comments

Graeme_Grant 1-Mar-17 7:36am

a neater solution...

Pete O'Hanlon 1-Mar-17 7:40am

Thanks - I have a similar solution for Dispatcher.Invoke :)

Graeme_Grant 1-Mar-17 7:43am

I have something similar but did a quick fix to the question asked.

Graeme_Grant 1-Mar-17 8:18am

my 5 too! :)