Delegates with return type

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Hi I have two methods with return type one being instance and the other one is static method. I am trying to access those methods with delegates but i am unable to access it i get a error " Has wrong return type

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Delgates_Ex1
{

    public delegate void ExampleDelgate (int x, int y);


    class Democlass
    {
        public int Add(int x, int y)

        {

            Console.WriteLine("Addition Method");
            return (x + y);
              
        }


        public static int mul(int x, int y)
        {
            Console.WriteLine("Multiplication Method");

            return (x * y);
        }

    }


    class Program
    {

        static void Main(string[] args)
        {
            Democlass d = new Democlass();

            ExampleDelgate ed = new ExampleDelgate(d.Add);

            ed(30, 10);

            Console.WriteLine("\n");

            ed = new ExampleDelgate(Democlass.mul);
            ed(30 * 10);

        }
    }
}

Posted 30-May-14 3:56am

ShaHam11

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3 solutions

Solution 3

In addition to the correct Solution 1:

You don't need a separate delegate type declaration for such a simple signature; it is already done for you and is System.Func<int, int, int>. You don't need a separate type declaration at all:

C#

System.Func<int, int, int> ed = new System.Func<int, int, int>(Demo.Mul);

Moreover, you don't even need a separate (named) method implementation:

C#

System.Func<int, int, int> ed = new System.Func<int, int, int>( (x, y) => {
    return x * y;
});

The special feature of using lambda: you can make the like shown above local in some method, not exposed anywhere else. Why would you need such a thing? For just one thing, please see my short article: Hide Ad-hoc Methods Inside the Calling Method’s Body[^].

—SA

Posted 30-May-14 5:35am

Sergey Alexandrovich Kryukov

Comments

Thomas Daniels 30-May-14 11:38am

Good addition, +5!

Solution 2

ProgramFOX has solved your problem, however you may also find this CodeProject article useful - C# - Delegates 101 - A Practical Example[^]

Posted 30-May-14 4:08am

CHill60

Comments

Thomas Daniels 30-May-14 10:11am

That article will indeed be useful for the OP, +5!

CHill60 30-May-14 11:45am

Thank you!

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Thomas Daniels · Accepted Answer · 2014-05-30T04:04:00

Solution 1

Change the return type of your delegate from void to int:

C#

public delegate int ExampleDelgate (int x, int y);

Also, when you try to access the mul method with a delegate, you should pass 30 and 10 as parameters and not as a multiplication:

C#

ed = new ExampleDelgate(Democlass.mul);
//ed(30 * 10); // remove this line
ed(30, 10); // add this

Posted 30-May-14 4:04am

Thomas Daniels

Comments

ShaHam11 30-May-14 10:07am

thank you for the solution

Thomas Daniels 30-May-14 10:07am

You're welcome!

Sergey Alexandrovich Kryukov 30-May-14 11:35am

5ed. Please see some extra ideas in Solution 3.
—SA

Thomas Daniels 30-May-14 11:38am

Thank you!