CODEWITHSUNDEEP
c#
Eddie Deyo
Eddie Deyo

Reputation: 5420

How do you invoke a method with any signature dynamically in C#?

I had a class with some common error handling code, and I wanted to pass in the method and arguments to call, but I couldn't quite come up with the syntax. What I want to do is roughly this:

private void InvokeHelper(Delegate method, params object[] args)
{
  bool retry = false;

  do
  {
    try
    {
      method.DynamicInvoke(args);
      retry = false;
    }
    catch (MyException ex)
    {
      retry = HandleException(ex);
    }
  } while (retry);
}

and then be able to do things like:

InvokeHelper(foo.MethodA, a, b, c);
InvokeHelper(foo.MethodB, x, y );

This gets a compiler error converting foo.MethodA and foo.MethodB into System.Delegate. I came up with the workaround below (and I actually like it better because then I get type checking on my arguments to my methods), but I'm curious if there's a way to do what I was originally trying to do? I know I could use foo.GetType().GetMethod("MethodA") and invoke that, but I was trying to avoid reflection. I mainly just want to understand how methods are dynamically invoked in .net.

Workaround:

private delegate void EmptyDelegate();

private void InvokeHelper(EmptyDelegate method)
{
  bool retry = false;

  do
  {
    try
    {
      method.Invoke();
      retry = false;
    }
    catch (MyException ex)
    {
      retry = HandleException(ex);
    }
  } while (retry);
}

then call:

InvokeHelper(delegate() { foo.MethodA(a, b, c); });
InvokeHelper(delegate() { foo.MethodB(x, y); });

Upvotes: 2

Views: 1230

Answers (2)

Amy B
Amy B

Reputation: 110161

Here's a re-write, following Will's advice to use Action:

    private void InvokeHelper(Action method)
    {
        bool retry = false;

        do
        {
            try
            {
                method();
                retry = false;
            }
            catch (MyException ex)
            {
                retry = HandleException(ex);
            }
        } while (retry);
    }

    public void Test()
    {
        FooClass foo = new FooClass();
        InvokeHelper( () => foo.MethodA(1, "b", 3) );
        InvokeHelper( () => foo.MethodB(2, "y"));
    }

Upvotes: 2

user1228
user1228

Reputation:

First off, your signature is 

private void InvokeHelper(Delegate method, params object[] args)

Yet you're making the mistake that you have to group your args into an array to call this method:

InvokeHelper(foo.MethodA, new object[] { a, b, c});

The parms keyword tells the compiler to do this for you; you can call this method thusly:

InvokeHelper(foo.MethodA, a, b, c);

Second, if you're targeting 3.0 or greater, don't use Delegate, use Action:

private void InvokeHelper(Action method)

and call it this way:

InvokeHelper(()=> MyMethodToInvoke(a, b, c));

which is just an overall better way of doing this.

As to why you're getting the compiler issue, its because System.Delegates hate us. Its a simple fact. That, and because there is no implicit cast from method group to Delegate.

Upvotes: 4

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