Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.IO;
using System.Collections;
using System.ComponentModel;

namespace ConsoleApplication1
{
    class BreakingChange
    {
        delegate void SampleDelegate(string x);

        public void CandidateAction(string x)
        {
            Console.WriteLine("Snippet.CandidateAction");
        }

        public class Derived : BreakingChange
        {
            public void CandidateAction(object o)
            {
                Console.WriteLine("Derived.CandidateAction");
            }
        }

        static void Main()
        {
            Derived x = new Derived();
            SampleDelegate factory = new SampleDelegate(x.CandidateAction);
            factory("test");
        }
    }
}

\Program.cs(32,38): warning CS1707: Delegate ‘ConsoleApplication1.BreakingChange.SampleDelegate’ bound to ‘ConsoleApplication1.BreakingChange.Derived.CandidateAction(object)’ instead of ‘ConsoleApplication1.BreakingChange.CandidateAction(string)’ because of new language rules
\Program.cs(23,25): (Related location)
\Program.cs(16,21): (Related location)

Question:
I know what causes this warning and know the reason behind it. However, I don’t know what the
best way to fix it?

1> Redefine the function (i.e.) change the function signature

2> Can we explicitly call BreakingChange.CandidateAction in the following line?

SampleDelegate factory = new SampleDelegate(x.CandidateAction);

Answer 1

Well, there are multiple ways to “fix” this, depending on what you want to, and can, do.

Personally I would add another overload to Derived that took a string, since you’re going to have the same issue with non-delegate calls as well.

public class Derived : BreakingChange
{
    public new void CandidateAction(string x)
    {
        base.CandidateAction(x);
    }

    public void CandidateAction(object o)
    {
        Console.WriteLine("Derived.CandidateAction");
    }
}

Or, since you know you want the base class method, you can cast the reference x:

new SampleDelegate(((BreakingChange)x).CandidateAction)