The Recaller Object

The business process management solution provides for retrying, in a generic way, some failed object method calls. The solution does this through the Recaller object in the ExceptionHandler orchestration. The ExceptionHandler orchestration uses the object to retry object method calls. For more information, see The ExceptionHandler Orchestration.

The Invoke Method

The Recaller object has a single, static method, Invoke. Because it is static, you never need to create an instance of the Recaller object. You can use the Invoke method in three ways: to construct an object, to call a static method for an object, or to call a non-static method for an object.

Note

The Invoke method serves as a wrapper for the Type.InvokeMember method in the .NET Framework Class Library.

Arguments for the Invoke Method

The following table describes arguments for the Invoke method:

Parameter	Type	Description
t	Type	The type of the object on which to call the method.
obj	Object	The instance of the object to use.
methodName	string	The name of the method to invoke.
args	Array	An array of type Object containing the method's arguments.

To call the constructor for an object, use an empty string ("") or null for methodName.

To call a static method, use null for obj.

To call a non-static method, supply all of the arguments.

Note

Using null as the value of the Type argument, t, causes Invoke to throw an ArgumentNullException exception. The argument t should not be null because the Invoke method uses the Type.InvokeMember .NET Framework method.

Calling Invoke

In the solution, only the ExceptionHandler orchestration uses the Recaller object. The ExceptionHandler is, in turn, used by other orchestrations. The values passed to the Invoke method come from these other orchestrations. For example, the following code appears in the Activate orchestration in the InitialException Expression shape:

Ex = CodeEx;  
ObjectType = orderHandler.GetType();  
CalledObject = orderHandler;  
Reason = "Standard Activate Failed";  
MethodName = "Activate";  
ParameterArray = System.Array.CreateInstance(typeof(System.Object),  
                                              3 );  
ParameterArray.SetValue(ServiceType, 0);  
ParameterArray.SetValue(OrderMsg.CustNum, 1);  
ParameterArray.SetValue(OrderMsg.OrderNum, 2);  
ReturnValue = null; // no return value expected  
  

Notice how the code creates an array using System.Array.CreateInstance and uses the SetValue method to store the values used in it.

After the Expression shape, the Activate orchestration calls the ExceptionHandler orchestration. The following code shows how the orchestration designer translates the Call shape:

call Microsoft.Samples.  
    BizTalk.SouthridgeVideo.  
        OrderManager.ExceptionHandlerOrch  
            (  
                Reason,  
                Ex,  
                CalledObject,  
                MethodName,   
                ParameterArray,   
                OrderCorrelation,   
                OrderMsg,   
                out ReturnValue,   
                ObjectType  
            );  
  

In the ExceptionHandler orchestration, the following code appears in the Call Original Code Expression shape:

ReturnValue =   
    Microsoft.Samples.  
        BizTalk.SouthridgeVideo.  
            Utilities.Recaller.  
                Invoke(  
                    ObjectType,  
                    CalledObject,  
                    MethodName,  
                    ParameterArray  
                );  

Notice that, although the argument names match those in the Activate orchestration's call, arguments are matched by order and not by name when calling orchestrations.

See Also

Implementation Highlights of the Business Process Management Solution
The ExceptionHandler Orchestration