c＃wpf dispatcher.begin调用冻结

Question

im working on an application which communicates with server.

thread  = new Thread(new ThreadStart(ClientStart));
thread.SetApartmentState(ApartmentState.STA);                
thread.Start();

private void ClientStart()
    {
        tcpClient = new TcpClient(ip,3000);
        stream = tcpClient.GetStream();
        while (true) {                
            stream.Read(...);
            PrintMessage(...);
        .....
        }
}
private void PrintMessage(LogWin w, string msg)
{
  DateTime dt = DateTime.Now;
  w.GetMessageBox().Dispatcher.BeginInvoke(DispatcherPriority.Input,new Action(()=>w.GetMessageBox()
            .AppendText(String.Format("{0:d/M/yyyy HH:mm:ss}", dt) + " : " + msg)));

}

later i need to print result to a messagebox. I know i have to use Dispatcher, because im working in another thread, but my application freezes even if i use beginInvoke method.

Edit based on Sheridan's answer :

now im getting: 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.

Dispatcher dispatcher = Dispatcher.CurrentDispatcher;
thread = new Thread(() => ClientStart(dispatcher));
thread.SetApartmentState(ApartmentState.STA);
thread.Start();

private void ClientStart(Dispatcher dispatcher)
    { 
....

and changed print method:

 dispatcher.BeginInvoke(DispatcherPriority.Input, new Action(() =>
       w.GetMessageBox()
            .AppendText(String.Format("{0:d/M/yyyy HH:mm:ss}", dt) + " : " + msg)));

solved by using Application.Current.Dispatcher

Answer 1

Always be wary of Dispatcher.CurrentDispatcher as that will will return an object for dispatching on the CURRENT thread - which may not be the UI. You want (and generally almost always want) the UI thread dispatcher.

You can get that through Application.Current.Dispatcher Which always returns the UI thread dispatcher.

Its frustating that these calls looks so similar...

[If you are in the main window you can just call Dispatcher but that probably not the case for you]

Answer 2

From the Dispatcher.BeginInvoke Method page on MSDN:

In WPF, only the thread that created a DispatcherObject may access that object

Therefore, if you first called the Dispatcher from your background thread, then it can only run on that background thread. Instead of that, ensure that you 'initialise' your Dispatcher object on the UI thread:

Dispatcher = Dispatcher.CurrentDispatcher;

From the Dispatcher Class page on MSDN:

If you attempt to get the CurrentDispatcher for the current thread and a Dispatcher is not associated with the thread, a Dispatcher will be created.

Then passing a reference to that UI thread Dispatcher to your background thread will enable you to access the UI thread again from the background thread.