Socket.SendAsync Method (SocketAsyncEventArgs)


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Sends data asynchronously to a connected Socket object.

Namespace:   System.Net.Sockets
Assembly:  System (in System.dll)

member SendAsync : 
        e:SocketAsyncEventArgs -> bool


Type: System.Net.Sockets.SocketAsyncEventArgs

The System.Net.Sockets.SocketAsyncEventArgs object to use for this asynchronous socket operation.

Return Value

Type: System.Boolean

Returns true if the I/O operation is pending. The SocketAsyncEventArgs.Completed event on 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 e parameter will not be raised and the e object passed as a parameter may be examined immediately after the method call returns to retrieve the result of the operation.

Exception Condition

The SocketAsyncEventArgs.Buffer or SocketAsyncEventArgs.BufferList properties on the e parameter must reference valid buffers. One or the other of these properties may be set, but not both at the same time.


A socket operation was already in progress using the System.Net.Sockets.SocketAsyncEventArgs object specified in the e parameter.


Windows XP or later is required for this method.


The Socket has been closed.


The Socket is not yet connected or was not obtained via an Accept, AcceptAsync,or BeginAccept, method.

The SendAsync method is used to write outgoing data from one or more buffers on a connection-oriented socket. This method can also be used, however, on connectionless sockets that have specified a remote host on a connect operation.

The SendAsync method starts an asynchronous send operation to the remote host established in the Accept, AcceptAsync, BeginAccept, BeginConnect, Connect, or ConnectAsync method.

The following properties and events on the System.Net.Sockets.SocketAsyncEventArgs object are required to successfully call this method:

The caller may set the SocketAsyncEventArgs.UserToken property to any user state object desired before calling the SendAsync 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.

The SendAsync method will throw an exception if you do not first call Accept, AcceptAsync, BeginAcceptBeginConnect, Connect, or ConnectAsync.

Calling the SendAsync method gives you the ability to send data within a separate execution thread.

For message-oriented sockets, do not exceed the maximum message size of the underlying Windows sockets service provider. If the data is too long to pass atomically through the underlying service provider, no data is transmitted and the SendAsync method throws a SocketException with the SocketAsyncEventArgs.SocketError set to the native Winsock WSAEMSGSIZE error code (10040).

Note that the successful completion of the SendAsync method does not indicate that the data was successfully delivered.

Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0
Available since 2.0
Windows Phone Silverlight
Available since 7.1
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