wcf chat application

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WCF

Hello everyone,

I am newbie to WCF, in fact i have no idea of wcf cooncepts. Now i am in a condotion where i need to complete a chat application using WCF. I have done a bit please help me how to proceed.

Here is my code
I have included 3 projects under single solution. One is library for interfaces

namespace WCF_interface
{
    [ServiceContract(CallbackContract=typeof(IClientCallback),SessionMode=SessionMode.Required)]
    public interface IServiceInterface
    {
        [OperationContract]
        void JoinChat(string username);
        [OperationContract]
        void SendMessageTo(string username, string message);
        [OperationContract]
        void LeaveChat(string username);
        [OperationContract]
        string[] GetOnlineUsersList();
        
       
        
    }
    public interface IClientCallback
    {
        [OperationContract(IsOneWay=true)]
        void ReceiveMessage(string sender, string message);
        [OperationContract(IsOneWay=true)]
        void UserEnter(string username);
        [OperationContract(IsOneWay=true)]
        void UserLeave(string username);

    }
}

Another is ChatServer

namespace ChatServer
{
    public partial class ChatServer : Form
    {
        ServiceHost host = null;
        public ChatServer()
        {
            InitializeComponent();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
           
        }
        private void button1_Click(object sender, EventArgs e)
        {
            host = new ServiceHost(typeof(ChatServerClass));
            host.AddServiceEndpoint(typeof(IServiceInterface), new NetTcpBinding("TcpBinding"), "net.tcp://localhost:2020/ChatService");
            host.Open();
            MessageBox.Show("Server Started");
            
            
        }
        private void button2_Click(object sender, EventArgs e)
        {
            host.Close();
            MessageBox.Show("server stopped");
        }

    }
}

and within ChatServe i have one more class which implements IServiceInterface

namespace ChatServer
{
    [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
    public class ChatServerClass : IServiceInterface
    {
        public delegate void UserJoin(string username);
        public delegate void SendMessage(string username, string message);
        public delegate void UserLeft(string username);
        public delegate void GetOnlineUsers(string username);

        public event UserJoin Newjoin;
        public event SendMessage MessageTo;
        public event UserLeft RemoveUser;
        public event GetOnlineUsers AvailableUsers;

              
        bool flag = true;
        List<string> ListofUsers = new List<string>();
        IClientCallback icallback;
        
                           
        [OperationBehavior]
        public void JoinChat(string name)
        {
            checkifuserexists(name);
            if (flag == true)
            {
                ListofUsers.Add(name);
               // Client cs = new Client();
               //Newjoin += new UserJoin(cs.Client_Newjoin);
               MessageBox.Show("User Logged in");
               //Newjoin(name);
            }
            else
                MessageBox.Show("Select other Name");
            
            ListofUsers.ToArray();
            
        }

        [OperationBehavior]
        public void SendMessageTo(string username, string message)
        {
            
            //Newjoin("hello");
        }
        public void ChatServerClass_Newjoin(string name)
        {
            //MessageBox.Show(name);
                                                                                    //Newjoin -= new UserJoin(ChatServerClass_Newjoin);
        }
        
        [OperationBehavior]
        public void LeaveChat(string username)
        {
            ListofUsers.Remove(username);
        }

        [OperationBehavior]
        public string[] GetOnlineUsersList()
        {
            return ListofUsers.ToArray();
        }

        

        public bool checkifuserexists(string name)
        {
            
            for (int i = 0; i < ListofUsers.Count; i++)
            {
                if (name == ListofUsers[i])
                {
                    flag = false;
                    break;
                }
                else
                    flag = true;

            }

            return flag;
        }

        
    }
}</string></string>

And My client side is

namespace WCF_ChatClient
{
    public partial class Client : Form,IClientCallback
    {
        
      
        IServiceInterface client;
        IClientCallback Icall;
        private string sel;
        List<string> ListofUsers = new List<string>();
        //public Dictionary<string,> ListofUsers = new Dictionary<string,>();
        DuplexChannelFactory<iserviceinterface> connect;
       private string username;

       
        public Client()
        {
            InitializeComponent();
            connect = new DuplexChannelFactory<iserviceinterface>(this, "TcpBinding");
            client = connect.CreateChannel();
            
            
        }

        
        public Client(string username)
        {
            this.username = username;
        }
        private void login_btn_Click(object sender, EventArgs e)
        {
            //Client newclient = new Client(login_txt.Text);
            username = login_txt.Text;
            //InstanceContext context = new InstanceContext(Icall);
            //connect.Open();
            client.JoinChat(username);
        }

        public void Client_Newjoin(string name)
        {
            this.login_txt.Focus();
            this.login_txt.ReadOnly = true;
            MessageBox.Show(name);
         }

        
        private void Send_btn_Click(object sender, EventArgs e)
        {
            
            client.SendMessageTo(username, sel);
            rtb_msg.Clear();
        }

        public void ReceiveMessage(string username, string message)
        {
            
        }
     

        public void UserEnter(string username)
        {
            
        }

        public void UserLeave(string username)
        {
        }

         private void button1_Click_1(object sender, EventArgs e)
        {
            client.LeaveChat(username);
             
        }

         private void UsersOnline_cmb_Click(object sender, EventArgs e)
         {
             UsersOnline_cmb.Items.Clear();
             string[] users = client.GetOnlineUsersList();
             foreach (string str in users)
                 UsersOnline_cmb.Items.Add(str);
         }

         private void UsersOnline_cmb_SelectedIndexChanged(object sender, EventArgs e)
         {
             sel = UsersOnline_cmb.SelectedItem.ToString();
         }

    }

  }</iserviceinterface></iserviceinterface></string></string>

The problem is i am not getting how to implement the callbacks and where exactly to implement the callbacks in my code. My client design page consists of textbox, login button, rich text box , and send button and combo box to show list of online users. PLease help me . I have gone through the COdeproject example of chat application but its usin xaml. THe client and server connection is established successfully. Please Help

Thank you