System.InvalidOperationException

Question

i have made a chatting application and i built wcf server side appliation which is to be started when the UI of the chatting application is started but each time i start the application the above picture gives details of my error

i keep getting this error

"System.InvalidOperationException: 'The callback contract of contract IChattingService either does not exist or does not define any operations. If this is not a duplex contract, consider using ChannelFactory instead of DuplexChannelFactory.'"

HERE IS THE IChattingService code:

namespace ChattingInterfaces  
{  
    [ServiceContract(CallbackContract = typeof(IClientContracts))]  
    public interface IChattingService  
    {  
        [OperationContract]  
        int Login(string userName);  
  
        [OperationContract]  
        void SendMessage(string message, string userName);  
  
        [OperationContract]  
        void Logout();  
    }  
}  

MAIN WINDOW CODE;

using ChattingInterfaces;  
using System;  
using System.ServiceModel;  
using System.Windows;  
  
namespace ChattingUI  
{  
    /// <summary>  
    /// Interaction logic for MainWindow.xaml  
    /// </summary>  
    public partial class MainWindow : Window  
    {  
        public static IChattingService Server;  
        private static DuplexChannelFactory<IChattingService> duplexChannelFactory;  
        public MainWindow()  
        {  
            InitializeComponent();  
  
            duplexChannelFactory = new DuplexChannelFactory<IChattingService>(new UserCallback(), "ChatServiceEndPoint");  
            Server = duplexChannelFactory.CreateChannel();  

        

Please some one should help me solve this problem i have tried to comprehend but i can't please help me out to start up my server and my UI at the same run time because i can't achieve this alone;
please help me out

Answer 1

Hi @Kwebena Acquah ,

"System.InvalidOperationException: 'The callback contract of contract IChattingService either does not exist or does not define any operations. If this is not a duplex contract, consider using ChannelFactory instead of DuplexChannelFactory.'"

As the error says. Maybe you can try to use ChannelFactory instead of DuplexChannelFactory, you can refer to the code below.
I didn't find a reference to wcf in your mainwindow code, e.g. using WindowsFormsApp1.ServiceReference1,
you can check the documentation on how to add a wcf reference.
https://learn.microsoft.com/en-us/visualstudio/data-tools/how-to-add-update-or-remove-a-wcf-data-service-reference?view=vs-2022

 public partial class MainWindow : Window  
     {  
         public MainWindow()  
         {  
             InitializeComponent();  
      
            BasicHttpBinding binding = new BasicHttpBinding();  
            EndpointAddress address = new EndpointAddress("***");  
  
            ChannelFactory<IChattingService> factory = new ChannelFactory<IChattingService>(binding, address);  
            
            Server = factory.CreateChannel();  
        }  
        public IChattingService Server { get; private set; }  
        public void RecieveMessage(string message, string userName)  
        {  
            textBox1.Text += DateTime.Now + "\n" + userName + ":" + message + "\n";  
        }  

Edit

    NetTcpBinding binding = new NetTcpBinding();    
    EndpointAddress addr = new EndpointAddress("net.tcp://localhost:8000/ChatService");    
    ChannelFactory<IChattingService> chn = new ChannelFactory<IChattingService>(binding, addr);    
    Server = chn.CreateChannel();    

Best regards,
Lan Huang

---

If the answer is the right solution, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.