How to: Create a One-Way Contract

Article
08/07/2009

This topic shows the basic steps to create methods that use a one-way contract. Such methods invoke operations on a Windows Communication Foundation (WCF) service from a client but do not expect a reply. This type of contract can be used, for example, to publish notifications to many subscribers. You can also use one-way contracts when creating a duplex (two-way) contract, which allows clients and servers to communicate with each other independently so that either can initiate calls to the other. This can allow, in particular, the server to make one-way calls to the client that the client can treat as events. For detailed information about specifying one-way methods, see the IsOneWay property and the OperationContractAttribute class.

For more information about creating a client application for a duplex contract, see How to: Access WCF Services with One-Way and Request-Reply Contracts. For a working sample, see the Service Contract: One-Way sample.

To create a one-way contract

Create the service contract by applying the ServiceContractAttribute class to the interface that defines the methods the service is to implement.
Indicate which methods in the interface a client can invoked by applying the OperationContractAttribute class to them.
Designate operations that must have no output (no return value and no out or ref parameters) as one-way by setting the IsOneWay property to true. Note that the operations that carry the OperationContractAttribute class satisfy a request-reply contract by default because the IsOneWay property is false by default. So you must explicitly specify the value of the attribute property to be true if you want a one-way contract for the method.

Example

The following code example defines a contract for a service that includes several one-way methods. All of the methods have one-way contracts except Equals, which defaults to request-reply and returns a result.

<ServiceContract(Namespace:="http://Microsoft.ServiceModel.Samples", SessionMode:=SessionMode.Required)> _
Public Interface ICalculatorSession

    <OperationContract(IsOneWay:=True)> _
    Sub Clear()
    <OperationContract(IsOneWay:=True)> _
    Sub AddTo(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub SubtractFrom(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub MultiplyBy(ByVal n As Double)
    <OperationContract(IsOneWay:=True)> _
    Sub DivideBy(ByVal n As Double)
    <OperationContract()> _
    Function Equal() As Double
End Interface

[ServiceContract(Namespace="http://Microsoft.ServiceModel.Samples", SessionMode=SessionMode.Required)]
public interface ICalculatorSession
{
    [OperationContract(IsOneWay=true)]
    void Clear();
    [OperationContract(IsOneWay = true)]
    void AddTo(double n);
    [OperationContract(IsOneWay = true)]
    void SubtractFrom(double n);
    [OperationContract(IsOneWay = true)]
    void MultiplyBy(double n);
    [OperationContract(IsOneWay = true)]
    void DivideBy(double n);
    [OperationContract]
    double Equals();
}

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How to: Create a One-Way Contract

To create a one-way contract

Example

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