Unity Application Block – Creating an Handler for exception application block

As mentioned in my previous post, Unity can be used to address cross cutting concerns by registering and invoking interceptors. In this post, I’ll show how to create an Exception handler for the enterprise library exception block using unity to reduce the cross concerns in your code for exception handling.

Step 1: Create ICallHanlder implementation

public class ExceptionCallHandler : ICallHandler

{

    public IMethodReturn Invoke(IMethodInvocation input, GetNextHandlerDelegate getNext)

    {

        var __Result = getNext()(input, getNext);

        if (__Result.Exception == null)

            return __Result;

        var __Rethrow = ExceptionPolicy.HandleException(__Result.Exception, "MyExceptionPolicy");

        if (__Rethrow) throw __Result.Exception;

        else throw new ArgumentException("An exception occured");

    }

    public int Order { get; set; }

}

Step 2: Create an attribute for Exception Handling

public class ExceptionCallHandlerAttribute : HandlerAttribute

{

    public override ICallHandler CreateHandler(Microsoft.Practices.Unity.IUnityContainer container)

    {

        return new ExceptionCallHandler();

    }

} 

Step 3: Use the handler attribute in your code.

[ExceptionCallHandler]

void Update(T instance);

Step 4: Configure the container

IUnityContainer ___Container = new UnityContainer();

___Container.AddNewExtension<Interception>();

___Container.RegisterType<IRepository<Employee, Guid>, EmployeeRepository>();

___Container.Configure<Interception>().SetDefaultInterceptorFor<IRepository<Employee, Guid>>(new TransparentProxyInterceptor());

It’s that simple to remove the try catch blocks from your code!!!