Create delegate with types known at runtime

问题:

How can I create a Delegate with types only known at run time ?

I would like to do the following :

Type type1 = someObject.getType();
Type type2 = someOtherObject.getType();   

var getter = (Func<type1, type2>)Delegate.CreateDelegate(
    typeof(Func<,>).MakeGenericType(type1, type2), someMethodInfo);

How can I achieve something similar ?

回答1:

I suspect you want Expression.GetFuncType as a simpler way of doing your typeof(...).MakeGenericType operation.

var delegateType = Expression.GetFuncType(type1, type2);
Delegate getter = Delegate.CreateDelegate(delegateType, someMethodInfo);

You can't have a compile-time type for getter that's more specific than Delegate though¹, because you simply don't know that type at compile-time. You could potentially use dynamic though, which would make it easier to invoke the delegate:

dynamic getter = ...;
var result = getter(input);

---

¹ As noted in comments, you could cast to MulticastDelegate, but it wouldn't actually buy you anything.

回答2:

You could create a generic method for that:

public Func<T1, T2> GetFunc<T1, T2>(T1 Object1, T2 Object2, MethodInfo Method)
{
    return (Func<T1, T2>)Delegate.CreateDelegate(typeof(Func<,>).MakeGenericType(typeof(T1), typeof(T2)), Method);
}

And I bet you can do something using the same philosophy with the Method to avoid all this reflection stuff.

Obs: that would work only if T1 and T2 are typed variables. If they are as object you'll get a Func<object, object>. But....if the objects you will give to the method are as object as well, that would be no problem at all. And maybe you can even use Func<object, object> always, depending on your scenario.