Postsharp Aspect with Async methods - postsharp

Question

I'm using Trial Ultimate version of PostSharp 4.0 but this doesn't work for me. Can you please check my code and advise. The error doesn't gets logged. And if i put the breakpoint doesn't hit onException method
This is code that I've written for Error handling Aspect
[Serializable]
public class MyMethodAspectAttribute : OnMethodBoundaryAspect
{
public MyMethodAspectAttribute()
{
this.ApplyToStateMachine = true;
}
public override void OnEntry(MethodExecutionArgs args)
{
Console.Write("Method Entry");
}
public override void OnException(MethodExecutionArgs args)
{
Console.Write(args.Exception.Message);
args.ReturnValue = null;
args.FlowBehavior = FlowBehavior.Return;
}
}
This is class where I've implemented this aspect
public class ErrorMethods
{
[MyMethodAspect]
public Task<int> Calculate(int i, int j)
{
var task = Task.Factory.StartNew(
() => i / j);
return task;
}
}
This is how I've used this method
private async void Button_Click(object sender, RoutedEventArgs e)
{
var obj = new ErrorMethods();
var result = await obj.Calculate(1, 0);
if (null == result)
{
MessageBox.Show("error");
}
}

Answer 1

The Calculate method in your example is not an async method, so setting ApplyToStateMachine aspect's property doesn't have effect on this method. The exception is thrown when a newly created task executes in the background and the aspect has no chance of catching it.
If you change your Calculate method to async method, then the async state machine execution can be intercepted by the aspect and OnException handler is invoked upon exception.
Note, however that setting the ReturnValue and FlowBehavior does not alter the flow of the state machine, so the exception will not be swallowed.
public class ErrorMethods
{
[MyMethodAspect]
public async Task<int> Calculate( int i, int j )
{
return await Task.Factory.StartNew( () => i / j );
}
}