Socket.ConnectAsync Method (SocketAsyncEventArgs)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Begins an asynchronous request for a remote host connection.
Assembly: System.Net (in System.Net.dll)
Return ValueType: System.Boolean
Returns true if the I/O operation is pending. The SocketAsyncEventArgs.Completed event on the System.Net.Sockets.SocketAsyncEventArgs object passed in the e parameter will be raised upon completion of the operation.
Returns false if the I/O operation completed synchronously. In this case, The SocketAsyncEventArgs.Completed event on the System.Net.Sockets.SocketAsyncEventArgs object passed in the e parameter will not be raised. The System.Net.Sockets.SocketAsyncEventArgs object passed in the e parameter may be examined immediately after the method call returns to retrieve the result of the operation.
An argument is not valid. This exception occurs if multiple buffers are specified, the SocketAsyncEventArgs.BufferList property is not null.
The SocketAsyncEventArgs.RemoteEndPoint cannot be null.
An error occurred when attempting to access the socket. See the Remarks section for more information.
The Socket has been closed.
A caller higher in the call stack does not have permission for the requested operation.
If you are using a connection-oriented protocol, the ConnectAsync method starts an asynchronous request for a connection to the remote host.
To be notified of completion, you must create a callback method that implements the EventHandler<SocketAsyncEventArgs> delegate and attach the callback to the SocketAsyncEventArgs.Completed event.
The following properties and events on the System.Net.Sockets.SocketAsyncEventArgs object are required:
The caller may set the SocketAsyncEventArgs.UserToken property to any user state object desired before calling the ConnectAsync method, so that the information will be retrievable in the callback method. If the callback needs more information than a single object, a small class can be created to hold the other required state information as members.
Optionally, a buffer may be provided which will atomically be sent on the socket after the ConnectAsync method succeeds. In this case, the SocketAsyncEventArgs.Buffer property needs to be set to the buffer containing the data to send and the SocketAsyncEventArgs.Count property needs to be set to the number of bytes of data to send from the buffer. Once a connection is established, this buffer of data is sent.
When using a connection-oriented protocol, the underlying service provider will assign the most appropriate local network address and local port number for the connection.
If you receive a SocketException when calling this method, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets Error Codes documentation in the MSDN library for a detailed description of the error.
For sockets, the security policy system affects cross-domain network access. A security policy is required for any connections from sockets.
// Create a socket and connect to the server Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); socketEventArg.Completed += new EventHandler<SocketAsyncEventArgs>(SocketEventArg_Completed); socketEventArg.RemoteEndPoint = hostEntry; socketEventArg.UserToken = sock; sock.ConnectAsync(socketEventArg);