在两个线程之间通信

Question

I have sth like that. It's giving me error. I cut out all unneeded parts of code. It is giving me this error

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

---

 public partial class MainWindow : Window
{
    BackgroundWorker worker;
    Grafik MainGrafik;

    double ProgressBar
    {
        set { this.progressBarMain.Value = value; }
    }

    public MainWindow()
    {
        InitializeComponent();
        worker = new BackgroundWorker();
        worker.DoWork += new DoWorkEventHandler(worker_DoWork);

        MainGrafik = new Grafik();
        MainGrafik.ProgressUpdate += 
            new Grafik.ProgressUpdateDelegate(MainGrafik_ProgressUpdate);

        worker.RunWorkerAsync();
    }

    void MainGrafik_ProgressUpdate(double progress)
    {
        ProgressBar = progress;
    }


    void worker_DoWork(object sender, DoWorkEventArgs e)
    {
        while(true)
        {
            MainGrafik.Refresh();
            Thread.Sleep(2000);
        }
    }
}

---

class Grafik
{
    public delegate void ProgressUpdateDelegate(double progress, 
        DateTime currTime);
    public event ProgressUpdateDelegate ProgressUpdate;

    public void Refresh()
    {
            ProgressUpdate(5); // Just for testing
    }
}

Answer 1

You can't update UI objects from another thread. They have to be updated in the UI thread. Try adding this code to the MainGrafik_ProgressUpdate(double progress)

void MainGragfik_ProgressUpdate(double progress)
{
    if (InvokeRequired)
    {
         BeginInvoke((MethodIvoker)(() =>
         {
             MainGragfik_ProgressUpdate(progress);
         }));

         return;
    }

    ProgressBar = progress;
}

Answer 2

The thread firing the ProgressUpdate event is your BackgroundWorker. The ProgressUpdate event handlers are likely running on that thread, and not the UI thread.

Answer 3

in short call this on the form in the context of your other thread's execution:

  void MainGrafik_ProgressUpdate(object sender, EventArgs e) { 
  Action<T> yourAction =>() yourAction;            

   if(yourForm.InvokeRequired)
        yourForm.Invoke(yourAction);
   else yourAction;

  }

Or with MethodInvoker (blank delegate)

 void MainGrafik_ProgressUpdate(object sender, EventArgs e) { 
     MethodInvoker invoker = delegate(object sender, EventArgs e) {

        this.ProgressBar = whatever progress;
  };        


  }