What happens when Exception occurs in a method in Multicast Delegate

Question

I would like to understand whats the best way to handle exceptions in Multicast delegates ?

My question is, what happens if a method throw exception in Multicast delegate execution ? Will it stop ? Continue ? How to handle ? A small program with explanation will be really helpful if somebody can share please.... thank you....

Answer 1

The exception will be propagated immediately, and any "later" actions in the delegate's invocation list will not get executed. If you want to make sure you execute all the delegates - perhaps aggregating all the exceptions together, for example - you'd need to call Delegate.GetInvocationList, cast each of those delegates to the same type as the original, and invoke them one by one, catching the exceptions as they were thrown.

Here's some sample code which does this - it would be nice to do this in a more generic way, ideally building a new delegate which (when executed) would execute all of the constituent delegates and aggregate the exceptions... but this is a start.

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

class Program
{
    public static void Main()
    {
        Action x = null;
        x += () => Console.WriteLine("First");
        x += () => { throw new Exception("Bang 1"); };
        x += () => { throw new Exception("Bang 2"); };
        x += () => Console.WriteLine("Second");

        try
        {
            ExecuteAll<Action>(x, action => action());
        }
        catch (AggregateException e)
        {
            Console.WriteLine(e);
        }
    }

    public static void ExecuteAll<T>(Delegate multi, Action<T> invoker)
    {
        List<Exception> exceptions = new List<Exception>();
        foreach (var single in multi.GetInvocationList())
        {
            try
            {
                invoker((T)(object)single);
            }
            catch (Exception e)
            {
                exceptions.Add(e);
            }
        }
        if (exceptions.Count > 0)
        {
            throw new AggregateException(exceptions);
        }
    }
}