.net - C# Cross-Thread communication

Question

in C#.NET , I've written the following simple background worker thread:

public class MyBackgrounder
{
    public delegate void dlgAlert();
    public dlgAlert Alert;
    public event EventHandler eventAlert;
    Thread trd;

    public void Start()
    {
        if (trd == null || trd.ThreadState == ThreadState.Aborted)
        {
            trd = new Thread(new ThreadStart(Do));
        }
        trd.IsBackground = true;
        trd.Priority = ThreadPriority.BelowNormal;
        trd.Start();
    }

    void Do()
    {

        Thread.Sleep(3000);
        Done();
    }

    void Done()
    {
        if (Alert != null)
            Alert();
        if (eventAlert != null)
            eventAlert(this, new EventArgs());
        Kill();
    }

    public void Kill()
    {
        if (trd != null)
            trd.Abort();
        trd = null;
    }
}


static class Program
{

    [STAThread]
    static void Main()
    {
        MyBackgrounder bg = new MyBackgrounder();
        bg.eventAlert += new EventHandler(bg_eventAlert);
        bg.Alert = jobDone;
        bg.Start();
    }

    static void bg_eventAlert(object sender, EventArgs e)
    {
        // here, current thread's id has been changed
    }

    static void jobDone()
    { 
        // here, current thread's id has been changed
    }

}

It just waits for 3 seconds (does its job) and then raises an specified event or calls a delegate. there's no problem until here and everything works fine. But when i watch the 'Thread.CurrentThread.ManagedThreadId' , i see it's the background thread! maybe it's normal , but how can i prevent this behavior? if you test the 'System.Windows.Forms.Timer' component and handle its 'Tick' event , you can see that the 'Thread.CurrentThread.ManagedThreadId' has not been changed from main thread Id to anything else.

what can i do?

Answer 1

If You are using Windows Forms you can do something like this:

1. In your Form add property

   private readonly System.Threading.SynchronizationContext context;
   public System.Threading.SynchronizationContext Context
   {
       get{ return this.context;}
   }
   

2. In Your Form constructor set the property

   this.context= WindowsFormsSynchronizationContext.Current;
   

3. Use this property to pass it to Your background worker as a constructor parameter. This way your worker will know about your GUI context. Create similar property inside Your background worker.

   private readonly System.Threading.SynchronizationContext context;
   public System.Threading.SynchronizationContext Context
   {
       get{ return this.context;}
   }
   
   public MyWorker(SynchronizationContext context)
   {
       this.context = context;
   }
   

4. Change your Done() method:

   void Done()
   {
       this.Context.Post(new SendOrPostCallback(DoneSynchronized), null);
   }
   
   void DoneSynchronized(object state)
   {
       //place here code You now have in Done method.
   }
   

5. In DoneSynchronized You should always be in Your GUI thread.