How to: Call WCF Service Operations Asynchronously

Run the ServiceModel Metadata Utility Tool (Svcutil.exe) tool with both the /async and the /tcv:Version35 command options together as shown in the following command.

svcutil /n:http://Microsoft.ServiceModel.Samples,Microsoft.ServiceModel.Samples http://localhost:8000/servicemodelsamples/service/mex /a /tcv:Version35

This generates, in addition to the synchronous and standard delegate-based asynchronous operations, a WCF client class that contains:

• Two <operationName>Async operations for use with the event-based asynchronous calling approach. For example:
  
  
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  public void AddAsync(double n1, double n2)
  {
      this.AddAsync(n1, n2, null);
  }
  
  public void AddAsync(double n1, double n2, object userState)
  {
      if ((this.onBeginAddDelegate == null))
      {
          this.onBeginAddDelegate = new BeginOperationDelegate(this.OnBeginAdd);
      }
      if ((this.onEndAddDelegate == null))
      {
          this.onEndAddDelegate = new EndOperationDelegate(this.OnEndAdd);
      }
      if ((this.onAddCompletedDelegate == null))
      {
          this.onAddCompletedDelegate = new System.Threading.SendOrPostCallback(this.OnAddCompleted);
      }
      base.InvokeAsync(this.onBeginAddDelegate, new object[] {
                  n1,
                  n2}, this.onEndAddDelegate, this.onAddCompletedDelegate, userState);
  }
  
  

• Operation completed events of the form <operationName>Completed for use with the event-based asynchronous calling approach. For example:
  
  
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  public event System.EventHandler<AddCompletedEventArgs> AddCompleted;
  
  

• System.EventArgs types for each operation (of the form <operationName>CompletedEventArgs) for use with the event-based asynchronous calling approach. For example:
  
  
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  [System.Diagnostics.DebuggerStepThroughAttribute()]
  [System.CodeDom.Compiler.GeneratedCodeAttribute("System.ServiceModel", "3.0.0.0")]
  public partial class AddCompletedEventArgs : System.ComponentModel.AsyncCompletedEventArgs
  {
      private object[] results;
      
      public AddCompletedEventArgs(object[] results, System.Exception exception, bool cancelled, object userState) : 
              base(exception, cancelled, userState)
      {       this.results = results;         }
      
      public double Result
      {
          get            {
              base.RaiseExceptionIfNecessary();
              return ((double)(this.results[0]));
          }
      }
  }
  
  

In the calling application, create a callback method to be called when the asynchronous operation is complete, as shown in the following sample code.

// Asynchronous callbacks for displaying results.
static void AddCallback(object sender, AddCompletedEventArgs e)
{
    Console.WriteLine("Add Result: {0}", e.Result);
}

Prior to calling the operation, use a new generic System.EventHandler of type <operationName>EventArgs to add the handler method (created in the preceding step) to the <operationName>Completed event. Then call the <operationName>Async method. For example:

// AddAsync
double value1 = 100.00D;
double value2 = 15.99D;
client.AddCompleted += new EventHandler<AddCompletedEventArgs>(AddCallback);
client.AddAsync(value1, value2);
Console.WriteLine("Add({0},{1})", value1, value2);