OperationContractAttribute.IsOneWay Property


Gets or sets a value that indicates whether an operation returns a reply message.

 property bool IsOneWay { bool get(); void set(bool value); };
public bool IsOneWay { get; set; }
member this.IsOneWay : bool with get, set
Public Property IsOneWay As Boolean

Property Value

true if this method receives a request message and returns no reply message; otherwise, false. The default is false.


The following example is a service that implements a service contract that specifies three operations. Two of the methods implement two-way operations, which return underlying response messages to the caller no matter what the return value is. The third method implements an operation that receives a call (an underlying inbound message) but returns no underlying response message.

public class OneAndTwoWay  
  // The client waits until a response message appears.  
  public int MethodOne (int x, out int y)  
    y = 34;  
    return 0;  

  // The client waits until an empty response message appears.  
  public void MethodTwo (int x)  

  // The client returns as soon as an outbound message  
  // is queued for dispatch to the service; no response  
  // message is generated or sent.  
  public void MethodThree (int x)  


Use the IsOneWay property to indicate that an operation does not return a reply message. This type of operation is useful for notifications or event-style communication, especially in two-way communication. Without waiting for an underlying response message, callers of one-way operations have no direct way to detect a failure in processing the request message. (Service applications that use reliable channels and one-way operations can detect a message delivery failure at the channel level. For details, see Reliable Sessions Overview.)

In duplex (or two-way) service-oriented applications in which the client and server communicate with each other independently, a client channel can use the IsOneWay property on its methods to indicate that the service can make one-way calls to the client that the client can treat as events. No return call or message is generated because the service does not expect any response message.

If the IsOneWay property is set to false (the default), even methods that return void result in a reply message. In this case, the infrastructure creates and sends an empty message to indicate to the caller that the method has returned. (Using this approach enables the infrastructure to send SOAP faults back to the client.) Setting IsOneWay to true is the only way to cancel the creation and dispatch of a response message.

One-way methods must not return a value or have ref or out parameters; otherwise a System.InvalidOperationException exception is thrown.

Specifying that an operation is a one-way operation means only that there is no response message. It is possible to block if a connection cannot be made, or the outbound message is very large, or if the service cannot read inbound information fast enough. If a client requires a non-blocking call, generate AsyncPattern operations. For more information, see One-Way Services and Accessing Services Using a WCF Client.

Applies to