How can I create an Action delegate from MethodInfo?

Question

I want to get an action delegate from a MethodInfo object. Is this possible?

Steviestevy

Answer 1

Use Delegate.CreateDelegate:

// Static method
Action action = (Action) Delegate.CreateDelegate(typeof(Action), method);

// Instance method (on "target")
Action action = (Action) Delegate.CreateDelegate(typeof(Action), target, method);

For an Action<T> etc, just specify the appropriate delegate type everywhere.

In .NET Core, Delegate.CreateDelegate doesn't exist, but MethodInfo.CreateDelegate does:

// Static method
Action action = (Action) method.CreateDelegate(typeof(Action));

// Instance method (on "target")
Action action = (Action) method.CreateDelegate(typeof(Action), target);

Morphine

Upvoted. How to apply this to DataEventArgs<T> ? #33376826 – Nictitate

Delegate.CreateDelegate does not appear to be available in .Net Core. Any ideas there? – Galer

@IAbstract: Interesting - I hadn't spotted that. You can call MethodInfo.CreateDelegate instead. (Just tried it, and it worked fine.) – Morphine

@JonSkeet: yeah, actually found that and appreciate adding to answer. +1 for completeness!!! – Galer

@JonSkeet [side-bar & food for thought] re: Delegate vs MethodInfo in try-catch blocks. I discovered the much perturbing failure of try-catch blocks when invoking a MethodInfo (e.g., obtained via reflection). However, if a delegate is created from the MethodInfo and cast to a Delegate sub-class - i.e., Action, Func - and executed in a try-catch block, any exceptions are caught as expected. – Galer

@IAbstract: That sounds very odd. Possibly ask about it in a new question? – Morphine

Can a parameter be passed into this delegate? – Acrylonitrile

@DouglasGaskell: Not an Action, no. If you want a delegate with an argument, pick a delegate with a signature matching what you want. – Morphine

Answer 2

This seems to work on top of John's advice too:

public static class GenericDelegateFactory
{
    public static object CreateDelegateByParameter(Type parameterType, object target, MethodInfo method) {

        var createDelegate = typeof(GenericDelegateFactory).GetMethod("CreateDelegate")
            .MakeGenericMethod(parameterType);

        var del = createDelegate.Invoke(null, new object[] { target, method });

        return del;
    }

    public static Action<TEvent> CreateDelegate<TEvent>(object target, MethodInfo method)
    {
        var del = (Action<TEvent>)Delegate.CreateDelegate(typeof(Action<TEvent>), target, method);

        return del;
    }
}

Bamboozle