Asynchronous web service requests

Asynchronous web service requests are useful when the mobile web service application is only occasionally connected to a network. With this method, a web service request is made by calling a method on the service binding class to place the request in an outgoing queue. The method returns a WSResult, which can be used to query the status of the response at a later time, even after the application has been restarted.

The following example makes an asynchronous request to get the USD-to-CAD exchange rate:

// C#
WSResult r = service.AsyncConversionRate( Currency.USD, Currency.CAD );
  
// Get the request ID.  Save it for later use if necessary.
string reqID = r.GetRequestID();

// Later: get the response for the specified request ID
WSResult r = service.GetResult( reqID );
if( r.GetStatus() == WSStatus.STATUS_RESULT_AVAILABLE ) {
  Console.WriteLine( "The conversion rate is " + r.GetDoubleValue( "ConversionRateResult" ) );
} else {
  Console.WriteLine( "Response not available" );
} 
// Java
WSResult r = service.asyncConversionRate( NET.webserviceX.Currency.USD, NET.webserviceX.Currency.CAD );
     
// Get the request ID.  Save it for later use if necessary.
String reqID = r.getRequestID();

// Later: get the response for the specified request ID
WSResult r = service.getResult( reqID );
if( r.getStatus() == WSStatus.STATUS_RESULT_AVAILABLE ) {
    System.out.println( "The conversion rate is " + r.getDoubleValue( "ConversionRateResult" ) );
} else {
    System.out.println( "Response not available" );
}

It is also possible to use a WSListener to get an asynchronous callback when the response to a web service request is available. For example:

// C#
// Make a request to get the USD to CAD exchange rate
WSResult r = service.AsyncConversionRate( Currency.USD, Currency.CAD );
  
// Register a listener for the result
service.SetListener( r.GetRequestID(), new CurrencyConvertorListener() );

// Java
// Make a request to get the USD to CAD exchange rate
WSResult r = service.asyncConversionRate( NET.webserviceX.Currency.USD, NET.webserviceX.Currency.CAD );
     
// Register a listener for the result
service.setListener( r.getRequestID(), new CurrencyConvertorListener() );

The WSListener interface defines two methods for handling asynchronous events:

OnResult An OnResult method is implemented to handle a response to a web service request. It is passed a WSResult object that represents the result of the web service request.
OnException An OnException method is implemented to handle errors that occurred during processing of the response to the web service request. It is passed a WSException object and a WSResult object. The WSException object contains information about the error that occurred, and the WSResult object can be used to obtain the request ID that the response corresponds to.

// C#
class CurrencyConvertorListener : WSListener
{
   public CurrencyConvertorListener() {
   }

   public void OnResult( WSResult r ) {
    try {
         USDToCAD._statusMessage = "USD to CAD currency exchange rate: " + r.GetDoubleValue( "ConversionRateResult" );
    } catch( Exception exc ) {
        USDToCAD._statusMessage = "Request " + r.GetRequestID() + " failed: " + exc.Message;
    }
   }

   public void OnException( WSException exc, WSResult r ) {
    USDToCAD._statusMessage = "Request " + r.GetRequestID() + " failed: " + exc.Message;
   }
} 
// Java
private class CurrencyConvertorListener implements WSListener
{
  public CurrencyConvertorListener() {
  }
 
  public void onResult( WSResult r ) {
   try {
        USDToCAD._statusMessage = "USD to CAD currency exchange rate: " + r.getDoubleValue( "ConversionRateResult" );
   } catch( Exception exc ) {
        USDToCAD._statusMessage = "Request " + r.getRequestID() + " failed: " + exc.getMessage();
   }
   }

   public void onException( WSException exc, WSResult r ) {
        USDToCAD._statusMessage = "Request " + r.getRequestID() + " failed: " + exc.getMessage();
   }
}

Discuss this page in DocCommentXchange.