Call child class method using dynamic keyword - c#-4.0

Question

I have several classes all implementing an interface IBar. Those classes are BarA, BarB, BarC.
I also have a base class Foo:
abstract class Foo
{
void Do(IBar bar)
{
Handle((dynamic)bar);
}
void Handle(IBar bar)
{
Console.Out.WriteLine("Fallback Scenario");
}
}
I want a child class FooChild like follows:
class FooChild : Foo
{
void Handle(BarA bar) {
Console.Out.WriteLine("Handling BarA");
}
void Handle(BarB bar) {
Console.Out.WriteLine("Handling Bar");
}
}
No I want to do the following, but I don't get the result I expect
var foo = new FooChild();
foo.Handle(new BarA()); // expected: Handling BarA, actual: Fallback Scenario
foo.Handle(new BarB()); // expected: Handling BarB, actual: Fallback Scenario
foo.Handle(new BarC()); // expected: Fallback Scenario, actual: Fallback Scenario
I can solve it by moving the Do(IBar bar) method to the FooChild class, but I don't want to do that. I might have 10 Foo childs and don't want to repeat that code. Is there a solution for this?

Answer 1

I think you want this:
void Do(IBar bar)
{
dynamic dynamicThis = this;
dynamicThis.Handle((dynamic) bar);
}
That way the method will be found against the actual type of this. Otherwise, the compiler remembers that the method was called from Foo, and only treats the argument dynamically, finding methods which would have been available from Foo with the actual type of bar. You want methods which would have been available from the actual type of this, as well as using the actual type of bar (via the cast to dynamic).
(You'll need to make the Handle methods public though.)