泛型接口（C# 编程）

原文链接：http://blog.csdn.net/u013108312/article/details/52051204
为泛型集合类或表示集合中项的泛型类定义接口通常很有用。对于泛型类，使用泛型接口十分可取，例如使用 IComparable 而不使用 IComparable，这样可以避免值类型的装箱和取消装箱操作。.NET Framework 类库定义了若干泛型接口，以用于 System.Collections.Generic 命名空间中的集合类。
将接口指定为类型参数的约束时，只能使用实现此接口的类型。下面的代码示例显示从 SortedList 类派生的 GenericList 类。有关更多信息，请参见 泛型介绍（C# 编程指南）。 SortedList 添加约束 where T : IComparable。这将使 SortedList 中的 BubbleSort 方法能够对列表元素使用泛型 CompareTo 方法。在此示例中，列表元素为简单类，即实现 Person 的 IComparable。

//Type parameter T in angle brackets.public class GenericList<T> : System.Collections.Generic.IEnumerable<T>{    protected Node head;    protected Node current = null;    // Nested class is also generic on T    protected class Node    {        public Node next;        private T data;  //T as private member datatype        public Node(T t)  //T used in non-generic constructor        {            next = null;            data = t;        }        public Node Next        {            get { return next; }            set { next = value; }        }        public T Data  //T as return type of property        {            get { return data; }            set { data = value; }        }    }    public GenericList()  //constructor    {        head = null;    }    public void AddHead(T t)  //T as method parameter type    {        Node n = new Node(t);        n.Next = head;        head = n;    }    // Implementation of the iterator    public System.Collections.Generic.IEnumerator<T> GetEnumerator()    {        Node current = head;        while (current != null)        {            yield return current.Data;            current = current.Next;        }    }    // IEnumerable<T> inherits from IEnumerable, therefore this class     // must implement both the generic and non-generic versions of     // GetEnumerator. In most cases, the non-generic method can     // simply call the generic method.    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()    {        return GetEnumerator();    }}public class SortedList<T> : GenericList<T> where T : System.IComparable<T>{    // A simple, unoptimized sort algorithm that     // orders list elements from lowest to highest:    public void BubbleSort()    {        if (null == head || null == head.Next)        {            return;        }        bool swapped;        do        {            Node previous = null;            Node current = head;            swapped = false;            while (current.next != null)            {                //  Because we need to call this method, the SortedList                //  class is constrained on IEnumerable<T>                if (current.Data.CompareTo(current.next.Data) > 0)                {                    Node tmp = current.next;                    current.next = current.next.next;                    tmp.next = current;                    if (previous == null)                    {                        head = tmp;                    }                    else                    {                        previous.next = tmp;                    }                    previous = tmp;                    swapped = true;                }                else                {                    previous = current;                    current = current.next;                }            }        } while (swapped);    }}// A simple class that implements IComparable<T> using itself as the // type argument. This is a common design pattern in objects that // are stored in generic lists.public class Person : System.IComparable<Person>{    string name;    int age;    public Person(string s, int i)    {        name = s;        age = i;    }    // This will cause list elements to be sorted on age values.    public int CompareTo(Person p)    {        return age - p.age;    }    public override string ToString()    {        return name + ":" + age;    }    // Must implement Equals.    public bool Equals(Person p)    {        return (this.age == p.age);    }}class Program{    static void Main()    {        //Declare and instantiate a new generic SortedList class.        //Person is the type argument.        SortedList<Person> list = new SortedList<Person>();        //Create name and age values to initialize Person objects.        string[] names = new string[]         {             "Franscoise",             "Bill",             "Li",             "Sandra",             "Gunnar",             "Alok",             "Hiroyuki",             "Maria",             "Alessandro",             "Raul"         };        int[] ages = new int[] { 45, 19, 28, 23, 18, 9, 108, 72, 30, 35 };        //Populate the list.        for (int x = 0; x < 10; x++)        {            list.AddHead(new Person(names[x], ages[x]));        }        //Print out unsorted list.        foreach (Person p in list)        {            System.Console.WriteLine(p.ToString());        }        System.Console.WriteLine("Done with unsorted list");        //Sort the list.        list.BubbleSort();        //Print out sorted list.        foreach (Person p in list)        {            System.Console.WriteLine(p.ToString());        }        System.Console.WriteLine("Done with sorted list");    }}

可将多重接口指定为单个类型上的约束，如下所示：

class Stack<T> where T : System.IComparable<T>, IEnumerable<T>{}

一个接口可定义多个类型参数，如下所示：

interface IDictionary<K, V>{}

适用于类的继承规则同样适用于接口：

interface IMonth<T> { }interface IJanuary     : IMonth<int> { }  //No errorinterface IFebruary<T> : IMonth<int> { }  //No errorinterface IMarch<T>    : IMonth<T> { }    //No error//interface IApril<T>  : IMonth<T, U> {}  //Error

如果泛型接口为逆变的，即仅使用其类型参数作为返回值，则此泛型接口可以从非泛型接口继承。在 .NET Framework 类库中，IEnumerable 从 IEnumerable 继承，因为 IEnumerable 只在 GetEnumerator 的返回值和 Current 属性 getter 中使用 T。
具体类可以实现已关闭的构造接口，如下所示：

interface IBaseInterface<T> { }class SampleClass : IBaseInterface<string> { }

只要类参数列表提供了接口必需的所有参数，泛型类便可以实现泛型接口或已关闭的构造接口，如下所示：

interface IBaseInterface1<T> { }interface IBaseInterface2<T, U> { }class SampleClass1<T> : IBaseInterface1<T> { }          //No errorclass SampleClass2<T> : IBaseInterface2<T, string> { }  //No error

对于泛型类、泛型结构或泛型接口中的方法，控制方法重载的规则相同。

原文链接：http://blog.csdn.net/u013108312/article/details/52051204