How to connect with a MessageWebSocket (XAML)

Article
08/31/2015

This topic will show you how to enable a Windows Store app to send and receive data by using a MessageWebSocket. This type of WebSocket object allows sections of a message to be read with each read operation. MessageWebSockets are typically used in scenarios where messages are not extremely large. Both UTF-8 and binary files are supported.

Prerequisites

The following examples use C# or C++ and are based on the WebSocket sample. For general help creating a Windows Runtime app using C# or Visual Basic, see Create your first Windows Runtime app using C# or Visual Basic. For general help creating a Windows Runtime app using C++, see Create your first Windows Runtime app using C++.

To ensure your Windows Runtime app is network ready, you must set any network capabilities that are needed in the project Package.appxmanifest file. If your app needs to connect as a client to remote services on the Internet, then the Internet (Client) capability is needed. If the app needs to connect as a client to remote services on a home network or work network, then the Home/Work Networking capability is needed.

Note On Windows Phone, there is only one network capability (Internet (Client & Server))which enables all network access for the app.

For more information, see How to set network capabilities.

Use a MessageWebSocket to send data

The code in this section creates a new MessageWebSocket, connects to a WebSocket server, and sends data to the server. Once a successful connection is established, the app waits for the MessageWebSocket.MessageReceived event to be invoked, indicating that data was received.

Note You may wish to display messages to the user or log that certain events have happened (for example, when a connection is made or when an error occurs).

Open the CS folder. Open your .cs file and add the following code.

private MessageWebSocket messageWebSocket;
private DataWriter messageWriter;

private async void Start_Click(object sender, RoutedEventArgs e)
   {
      try
      {
         // Make a local copy to avoid races with Closed events.
         MessageWebSocket webSocket = messageWebSocket;

         // Have we connected yet?
         if (webSocket == null)
         {
            Uri server = new Uri(ServerAddressField.Text.Trim());

            webSocket = new MessageWebSocket();
            // MessageWebSocket supports both utf8 and binary messages.
            // When utf8 is specified as the messageType, then the developer
            // promises to only send utf8-encoded data.
            webSocket.Control.MessageType = SocketMessageType.Utf8;
            // Set up callbacks
            webSocket.MessageReceived += MessageReceived;
            webSocket.Closed += Closed;

            await webSocket.ConnectAsync(server);
            messageWebSocket = webSocket; // Only store it after successfully connecting.
            messageWriter = new DataWriter(webSocket.OutputStream);
         }

         string message = InputField.Text;

         // Buffer any data we want to send.
         messageWriter.WriteString(message);

         // Send the data as one complete message.
         await messageWriter.StoreAsync();

       }
       catch (Exception ex) // For debugging
       {
          WebErrorStatus status = WebSocketError.GetStatus(ex.GetBaseException().HResult);
          // Add your specific error-handling code here.
       }
   }

Register your callback for the MessageWebSocket.MessageReceived event

When the MessageWebSocket.MessageReceived event occurs, the registered callback is called and receives data from MessageWebSocketMessageReceivedEventArgs.

Add the following code to your .cs file.

private void MessageReceived(MessageWebSocket sender, MessageWebSocketMessageReceivedEventArgs args)
   {
      try
      {
         using (DataReader reader = args.GetDataReader())
         {
            reader.UnicodeEncoding = Windows.Storage.Streams.UnicodeEncoding.Utf8;
            string read = reader.ReadString(reader.UnconsumedBufferLength);
         }
      }  
      catch (Exception ex) // For debugging
      {
         WebErrorStatus status = WebSocketError.GetStatus(ex.GetBaseException().HResult);
         // Add your specific error-handling code here.
      }
   }

Register your callback for the MessageWebSocket.Closed event

When the MessageWebSocket.Closed event occurs, the registered callback is called and receives data from WebSocketClosedEventArgs to close the connection.

Add the following code to your .cs file.

private void Closed(IWebSocket sender, WebSocketClosedEventArgs args)
   {
      // You can add code to log or display the code and reason
      // for the closure (stored in args.Code and args.Reason)

      // This is invoked on another thread so use Interlocked 
      // to avoid races with the Start/Close/Reset methods.
      MessageWebSocket webSocket = Interlocked.Exchange(ref messageWebSocket, null);
      if (webSocket != null)
      {
         webSocket.Dispose();
      }
   }