Csharp 简明教程

C

Generics 允许您定义类或方法中编程元素的数据类型规范，直到它在程序中实际使用。换句话说，泛型允许您编写可处理任何数据类型的类或方法。

Generics allow you to define the specification of the data type of programming elements in a class or a method, until it is actually used in the program. In other words, generics allow you to write a class or method that can work with any data type.

您使用数据类型的备用参数编写类或方法的规范。当编译器遇到类的构造函数或方法的函数调用时，它会生成代码来处理特定数据类型。一个简单的示例有助于理解这个概念 −

You write the specifications for the class or the method, with substitute parameters for data types. When the compiler encounters a constructor for the class or a function call for the method, it generates code to handle the specific data type. A simple example would help understanding the 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) {

         //declaring an int array
         MyGenericArray<int> intArray = new MyGenericArray<int>(5);

         //setting values
         for (int c = 0; c < 5; c++) {
            intArray.setItem(c, c*5);
         }

         //retrieving the values
         for (int c = 0; c < 5; c++) {
            Console.Write(intArray.getItem(c) + " ");
         }

         Console.WriteLine();

         //declaring a character array
         MyGenericArray<char> charArray = new MyGenericArray<char>(5);

         //setting values
         for (int c = 0; c < 5; c++) {
            charArray.setItem(c, (char)(c+97));
         }

         //retrieving the values
         for (int c = 0; c< 5; c++) {
            Console.Write(charArray.getItem(c) + " ");
         }
         Console.WriteLine();

         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

0 5 10 15 20
a b c d e

Features of Generics

泛型是一种用以下方式丰富您的程序的技术 −

Generics is a technique that enriches your programs in the following ways −

It helps you to maximize code reuse, type safety, and performance.
You can create generic collection classes. The .NET Framework class library contains several new generic collection classes in the System.Collections.Generic namespace. You may use these generic collection classes instead of the collection classes in the System.Collections namespace.
You can create your own generic interfaces, classes, methods, events, and delegates.
You may create generic classes constrained to enable access to methods on particular data types.
You may get information on the types used in a generic data type at run-time by means of reflection.

Generic Methods

在前面的示例中，我们使用了一个泛型类；我们可以用一个类型参数声明一个泛型方法。下面的程序说明了这个概念：

In the previous example, we have used a generic class; we can declare a generic method with a type parameter. The following program illustrates the 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 swap:
         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 values after swap:
         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();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

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

Generic Delegates

您可以用类型参数定义一个泛型委托。例如：

You can define a generic delegate with type parameters. For example −

delegate T NumberChanger<T>(T n);

下面的示例展示了这个委托的用法：

The following example shows use of this delegate −

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 delegate instances
         NumberChanger<int> nc1 = new NumberChanger<int>(AddNum);
         NumberChanger<int> nc2 = new NumberChanger<int>(MultNum);

         //calling the methods using the delegate objects
         nc1(25);
         Console.WriteLine("Value of Num: {0}", getNum());

         nc2(5);
         Console.WriteLine("Value of Num: {0}", getNum());
         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Value of Num: 35
Value of Num: 175