C＃ - 将Delegate作为参数传递给方法

Question

I am trying to get familiar with the concept of delegates in C#. I have created this console application so far:

Program.cs

using System;

namespace DelegatesTest
{
    class Program
    {
        static void Main(string[] args)
        {
            ArithmeticOperation.ArOpDel additionDelegate = new ArithmeticOperation.ArOpDel(ArithmeticOperation.Addition);
            Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate(10, 5)));
            Console.ReadKey();
        }
    }
}

ArithmeticOperation.cs

using System;

namespace DelegatesTest
{
    public static class ArithmeticOperation
    {
        public delegate int ArOpDel(int x, int y);

        public static string ConvertResultToString(ArOpDel del)
        {
            string result = String.Format("The result of the {0} operation is {1}", del.Method.Name, del.ToString());
            return result;
        }

        public static int Addition(int x, int y)
        {
            return x + y;
        }

        public static int Subtraction(int x, int y)
        {
            return x - y;
        }

        public static int Multiplication(int x, int y)
        {
            return x * y;
        }

        public static int Division(int x, int y)
        {
            return x / y;
        }
    }
}

As you can see from the code, I am using a static class called ArithmeticOperation.cs to perform some arithmetic operations. The ConvertResultToString method takes one of the arithmetic operations methods as a parameter in order to display the result elegantly as a string.

Unfortunately, my code does not compile. It is giving me the following error:

Argument '1': cannot convert from 'int' to 'DelegatesTest.ArithmeticOperation.ArOpDel'

The error is being given on this line:

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate(10, 5)));

Can you please help me solve this problem as I am not very experienced with delegates? In fact, I have created this application to learn about delegates.

Answer 1

additionDelegate(10, 5) deleagate additionDelegate(10, 5)将通过算术运算返回int ，它不会返回deleagate ，这是编译错误的原因。

Answer 2

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate(10, 5)));

You are not passing the delegate here. You are calling it, which results in an int .

This would pass the delegate:

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate));

You would need to actually call the delegate somewhere though.

Answer 3

when you do this

 Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate(10, 5)));

you are forcing the compiler to execute the method and return the result to pass it as an argument which in this case it's an int while the ConvertResultTostring expect a delegate here how you can get it work without using generic

 class Program
    {
        static void Main(string[] args)
        {
            ArithmeticOperation.ArOpDel additionDelegate = ArithmeticOperation.Addition;

            Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate,5,6));
            Console.ReadKey();
        }
    }
    public static class ArithmeticOperation
    {
        public delegate int ArOpDel(int x, int y);

        public static string ConvertResultToString(ArOpDel del,int x, int y )
        {
            string result = String.Format("The result of the {0} operation is {1}", del.Method.Name, del(x,y).ToString());
            return result;
        }

        public static int Addition(int x, int y)
        {
            return x + y;
        }

        public static int Subtraction(int x, int y)
        {
            return x - y;
        }

        public static int Multiplication(int x, int y)
        {
            return x * y;
        }

        public static int Division(int x, int y)
        {
            return x / y;
        }
    }

Answer 4

additionDelegate(10, 5) is an invocation of additionDelegate which actually is an Addition function. So, the result is an integer.

In order to pass a delegate you should pass additionDelegate itself instead of additionDelegate(10, 5) . But, in this case, the result of the operation will not be available in ConvertResultToString unless you invoke it there.

public static string ConvertResultToString(ArOpDel del)
{
     string result = String.Format("The result of the {0} operation is {1}", del.Method.Name, del(10, 5).ToString());
     return result;
}

...

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate));

Answer 5

additionDelegate(10, 5) means invoke the delegate,the result is an int type which does not match the ConvertResultToString method stub. you need change

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate(10, 5)))

to

Console.WriteLine(ArithmeticOperation.ConvertResultToString(additionDelegate))

and change

string result = String.Format("The result of the {0} operation is {1}", del.Method.Name, del.ToString()); 

to

string result = String.Format("The result of the {0} operation is {1}", del.Method.Name, del(10,5).ToString());