C [advanced part] C generic [need to be further supplemented: generic interfaces and instances of generic events]

C# Learning summary - General catalogue

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Preface

Generic （Generic） Allow you to Delay writing specifications for data types of programming elements in a class or method , Until it's actually used in the program . let me put it another way , Generics allow you to Write a class or method that can work with any data type .

You can Write the specification of a class or method through alternative parameters of a data type . When the compiler encounters a function call of a class's constructor or method , It generates code to handle the specified data type . The following simple example will help you understand this concept ：

using System;
using System.Collections.Generic;

namespace GenericApplication
{
    
    public class MyGenericArray<T>
    {
    
        private T[] array;
        public MyGenericArray(int size)
        {
    
            array = new T[size + 1];
        }
        public T getItem(int index)
        {
    
            return array[index];
        }
        public void setItem(int index, T value)
        {
    
            array[index] = value;
        }
    }
           
    class Tester
    {
    
        static void Main(string[] args)
        {
    
            //  Declare an integer array 
            MyGenericArray<int> intArray = new MyGenericArray<int>(5);
            //  Set the value 
            for (int c = 0; c < 5; c++)
            {
    
                intArray.setItem(c, c*5);
            }
            //  Get value 
            for (int c = 0; c < 5; c++)
            {
    
                Console.Write(intArray.getItem(c) + " ");
            }
            Console.WriteLine();
            //  Declare a character array 
            MyGenericArray<char> charArray = new MyGenericArray<char>(5);
            //  Set the value 
            for (int c = 0; c < 5; c++)
            {
    
                charArray.setItem(c, (char)(c+97));
            }
            //  Get value 
            for (int c = 0; c < 5; c++)
            {
    
                Console.Write(charArray.getItem(c) + " ");
            }
            Console.WriteLine();
            Console.ReadKey();
        }
    }
}

Running results ：

0 5 10 15 20
a b c d e

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Generic （Generic） Characteristics of

Using generics is a technique to enhance program functionality , Specifically in the following aspects ：

• It helps you maximize reuse of code 、 Protect types of security and improve performance .
• You can create generic collection classes ..NET The class library is in the framework System.Collections.Generic The namespace contains some new generic collection classes . You can use these generic collection classes instead of System.Collections Set class in .
• You can create your own generic interfaces 、 Generic classes 、 Generic methods 、 Generic events and generic delegates .
• You can constrain generic classes to access methods of specific data types .
• Information about the types used in generic data types can be obtained at run time by using reflection .

Generic methods

In the example above , We have used generic classes , We can declare generic methods through type parameters . The following procedure illustrates this concept ：

using System;
using System.Collections.Generic;

namespace GenericMethodAppl
{
    
    class Program
    {
    
        static void Swap<T>(ref T lhs, ref T rhs)
        {
    
            T temp;
            temp = lhs;
            lhs = rhs;
            rhs = temp;
        }
        static void Main(string[] args)
        {
    
            int a, b;
            char c, d;
            a = 10;
            b = 20;
            c = 'I';
            d = 'V';

            //  Display values before switching 
            Console.WriteLine("Int values before calling swap:");
            Console.WriteLine("a = {0}, b = {1}", a, b);
            Console.WriteLine("Char values before calling swap:");
            Console.WriteLine("c = {0}, d = {1}", c, d);

            //  call  swap
            Swap<int>(ref a, ref b);
            Swap<char>(ref c, ref d);

            //  Display the value after the exchange 
            Console.WriteLine("Int values after calling swap:");
            Console.WriteLine("a = {0}, b = {1}", a, b);
            Console.WriteLine("Char values after calling swap:");
            Console.WriteLine("c = {0}, d = {1}", c, d);
            Console.ReadKey();
        }
    }
}

Running results ：

Int values before calling swap:
a = 10, b = 20
Char values before calling swap:
c = I, d = V
Int values after calling swap:
a = 20, b = 10
Char values after calling swap:
c = V, d = I

Commissioned by the generic

You can define generic delegates through type parameters . for example ：

delegate T NumberChanger<T>(T n);

The following example demonstrates the use of delegates ：

using System;
using System.Collections.Generic;

delegate T NumberChanger<T>(T n);
namespace GenericDelegateAppl
{
    
    class TestDelegate
    {
    
        static int num = 10;
        public static int AddNum(int p)
        {
    
            num += p;
            return num;
        }

        public static int MultNum(int q)
        {
    
            num *= q;
            return num;
        }
        public static int getNum()
        {
    
            return num;
        }

        static void Main(string[] args)
        {
    
            //  Create a delegate instance 
            NumberChanger<int> nc1 = new NumberChanger<int>(AddNum);
            NumberChanger<int> nc2 = new NumberChanger<int>(MultNum);
            //  Use a delegate object to call a method 
            nc1(25);
            Console.WriteLine("Value of Num: {0}", getNum());
            nc2(5);
            Console.WriteLine("Value of Num: {0}", getNum());
            Console.ReadKey();
        }
    }
}

When the above code is compiled and executed , It will produce the following results ：

Value of Num: 35
Value of Num: 175

summary

C# Learning summary - General catalogue