callback class to update wpf UI

Question

I am creating a chatting app using WCF-Duplex and WPF. Is there is any way to call a UI function when the callback method (which is in another class than the UI) is invoked from the server?!

Here is a sample of my classes:

Service:

[ServiceContract( 
    Name = "GPH_QuickMessageService",
    Namespace = "TextChat",
    SessionMode = SessionMode.Required,
    CallbackContract = typeof(IMessageServiceCallback))]

        public interface IMessageServiceInbound
        {
            [OperationContract]
            int JoinTheConversation(string userName);

        }   public interface IMessageServiceCallback
        {
            [OperationContract(IsOneWay = true)]
            void NotifyUserJoinedTheConversation(string userName);
        }

The JoinTheConversation invokes NotifyUserJoinedTheConversation method at the client

The Client: The Form:

           public partial class Account : Window 
    {
      public Account()
        {
           InitializeComponent();

        }
      public void updateUsersInConversation(string username)
       {
             TreeViewItem item = new TreeViewItem();
             item.Header = username;
             contactsTree.Children.Add(item);
       }
   }

The callback implementation at the client

[CallbackBehavior(UseSynchronizationContext = false)]
public class ChatCallBack : GPH_QuickMessageServiceCallback, IDisposable
{

    public ChatCallBack()
    {
        //UIContext = context;
    }

    public void NotifyUserJoinedTheConversation(string userName)
    {
        MessageBox.Show("IN CLIENT");
        //I want to call updateUsersInConversation in the UI class
    }
  }

I searched alot and found a lot of things about delegation and SendOrPostCallBack but I just couldn't link all these things together. I am sorry for the long post and hope anyone can help me with that

It is the class that implements the callback functions for the WCF service at the client — Shereen, May 26 '14 at 18:35

score 1 · Accepted Answer · edited May 23 '17 at 11:57

You can try with Dispatcher.Invoke() inside an Event Handler registered in your Account class.

More info here: How to update UI from another thread running in another class

[Edit] Some code example:

class ChatCallBack 
{
    public event EventHandler<string> UserJoinedTheConversation;

    public void NotifyUserJoinedTheConversation(string username)
    {
        var evt = UserJoinedTheConversation;
        if (evt != null)
            evt(this, username);
    }

    //other code
}

And in you Account Class:

private ChatCallBack chatCallBack;
public Account() //class constructor
{
    InitializeComponent();
    chatCallBack = new ChatCallBack();
    chatCallBack.UserJoinedTheConversation += (sender, username) =>
    {
        Dispatcher.Invoke(() => updateUsersInConversation(username));
    };
}

Sajeetharan · Answer 2 · 2014-05-26T19:12:09.617

You can do this,

Create a method to return the Instance of the MainWindow,

 public static Account _this;

        public Account()
        {
            InitializeComponent();
            _this = this;

        }
        public void updateUsersInConversation(string username)
        {
            TreeViewItem item = new TreeViewItem();
            item.Header = username;
            //contactsTree.Children.Add(item);
        }
        public  static Account GetInstance()
        {
            return _this;
        }

And in your Client call back class, you can invoke the method like this

        public void NotifyUserJoinedTheConversation(string userName)
        {
          Account temp = Account.GetInstance();
          temp.updateUsersInConversation("test");
        }

It gives me an error saying that I can't update the UI elements because it is in a different thread. — Shereen, May 26 '14 at 23:41

callback class to update wpf UI

2 Answers2