Question

I am able to open a new window in a new thread by the following code.

The following code is from MainWindow.xaml.cs

private void buttonStartStop_Click(object sender, RoutedEventArgs e)
{    

  Test test = new Test();

  Thread newWindowThread = new Thread(new ThreadStart(test.start));
  newWindowThread.SetApartmentState(ApartmentState.STA);
  newWindowThread.IsBackground = true;
  newWindowThread.Start();
}

and the following from test.start()

public void start()
{

  OutputWindow outputwindow = new OutputWindow();
  outputwindow.Show();


  Output.print("Begin");
  System.Windows.Threading.Dispatcher.Run();
  Output.print("FINAL");
  System.Windows.Threading.Dispatcher.Run();

}

And the following is from the Output class

public static void print(String str)
{
  Dispatcher uiDispatcher = OutputWindow.myOutputWindow.Dispatcher;
  uiDispatcher.BeginInvoke(new Action(delegate() { OutputWindow.myOutputWindow.textBoxOutput.AppendText(str + "\n"); }));
  uiDispatcher.BeginInvoke(new Action(delegate() { OutputWindow.myOutputWindow.textBoxOutput.ScrollToLine(OutputWindow.myOutputWindow.textBoxOutput.LineCount - 1); }));
}

public static void printOnSameLine(String str)
{
  Dispatcher uiDispatcher = OutputWindow.myOutputWindow.Dispatcher;
  uiDispatcher.BeginInvoke(new Action(delegate() { OutputWindow.myOutputWindow.textBoxOutput.AppendText(str); }));
  uiDispatcher.BeginInvoke(new Action(delegate() { OutputWindow.myOutputWindow.textBoxOutput.ScrollToLine(OutputWindow.myOutputWindow.textBoxOutput.LineCount - 1); }));
}

“Begin” Does get printed in the textbox but “FINAL” does not, I want the start method in Test class to update the textbox in outputwindow through out the program. What is the best way to do this?

Thank you in advance

Answer 1

I’m not sure what are you trying to do. It is normal that FINAL does not print because you called System.Windows.Threading.Dispatcher.Run(). This method keeps thread alive and listens for events. You can look at it like if you have while(true){} inside the Run method. Method will continue to run until Dispatcher is shutdown. You should keep background thread alive and call your static methods from another thread when you need to set a message. Here’s an example:

        // reference to window in another thread
        Window outputWindow = null;

        Thread thread = new Thread(() =>
        {
            // another thread
            outputWindow = new Window();
            outputWindow.Show();
            // run event loop
            System.Windows.Threading.Dispatcher.Run();
        }) { ApartmentState = ApartmentState.STA, IsBackground = true };
        thread.Start();

        while (outputWindow == null)
        {
            // wait until the window in another thread has been created
            Thread.Sleep(100);
        }

        // simulate process
        for (int i = 0; i < 10; i++)
        {
            outputWindow.Dispatcher.BeginInvoke((Action)(() => { outputWindow.Title = i.ToString(); }), System.Windows.Threading.DispatcherPriority.Normal);
            Thread.Sleep(500); // simulate some hard work so we can see the change on another window's title
        }

        // close the window or shutdown dispatcher or abort the thread...
        thread.Abort();

EDIT:

This could be quick & dirty generic solution. DoSomeHardWork creates another GUI thread for wait window which displays progress information. This window creates work thread which actually does the work. Work is implemented in method Action. 1st argument is wait window so you can change it from work thread. Of course, in the real world you should go through interface and not directly to window implementation but this is just an example. 2nd argument is object so you can pass whatever you need to the work thread. If you need more arguments pass object[] or modify method signature. In this example I simulate hard work with counter and sleep. You can execute this code on button click multiple times and you will see all wait windows counting their own counter without freezing. Here is the code:

    public static void DoSomeHardWork(Action<Window, object> toDo, object actionParams)
    {
        Thread windowThread = new Thread(() =>
        {
            Window waitWindow = new Window();
            waitWindow.Loaded += (s, e) =>
            {
                Thread workThread = new Thread(() =>
                {
                    // Run work method in work thread passing the
                    // wait window as parameter
                    toDo(waitWindow, actionParams);
                }) { IsBackground = true };
                // Start the work thread.
                workThread.Start();
            };
            waitWindow.Show();
            Dispatcher.Run();
        }) { ApartmentState = ApartmentState.STA, IsBackground = true };
        // Start the wait window thread.
        // When window loads, it will create work thread and start it.
        windowThread.Start();
    }

    private void MyWork(Window waitWindow, object parameters)
    {
        for (int i = 0; i < 10; i++)
        {
            // Report progress to user through wait window.
            waitWindow.Dispatcher.BeginInvoke((Action)(() => waitWindow.Title = string.Format("{0}: {1}", parameters, i)), DispatcherPriority.Normal);
            // Simulate long work.
            Thread.Sleep(500);
        }
        // The work is done. Shutdown the wait window dispather.
        // This will stop listening for events and will eventualy terminate
        // the wait window thread.
        waitWindow.Dispatcher.InvokeShutdown();
    }

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        DoSomeHardWork(MyWork, DateTime.Now);
    }