泛型接口(C# 编程指南)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<T> 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 2.0 类库定义了若干新的泛型接口,以用于 System.Collections.Generic 命名空间中新的集合类。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 GenericList<T> 类派生的 SortedList<T> 类。有关更多信息,请参见泛型介绍(C# 编程指南)。SortedList<T> 添加了约束 where T : IComparable<T>。这将使 SortedList<T> 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 IComparable<Person> 的 Person。 C# 复制代码 //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:C# 复制代码 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:C# 复制代码 interface IDictionary<K, V> { } 类之间的继承规则同样适用于接口:C# 复制代码 interface IMonth<T> { }interface IJanuary : IMonth<int> { } //No error interface IFebruary<T> : IMonth<int> { } //No error interface 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<T> 从 IEnumerable 继承,因为 IEnumerable<T> 仅在 GetEnumerator 的返回值和当前属性 getter 中使用 T。具体类可以实现已关闭的构造接口,如下所示:C# 复制代码 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:C# 复制代码 interface IBaseInterface1<T> { } interface IBaseInterface2<T, U> { }class SampleClass1<T> : IBaseInterface1<T> { } //No error class SampleClass2<T> : IBaseInterface2<T, string> { } //No error
//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:C# 复制代码
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:C# 复制代码
interface IDictionary<K, V>
{
}
类之间的继承规则同样适用于接口:C# 复制代码
interface IMonth<T> { }interface IJanuary : IMonth<int> { } //No error
interface IFebruary<T> : IMonth<int> { } //No error
interface 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<T> 从 IEnumerable 继承,因为 IEnumerable<T> 仅在 GetEnumerator 的返回值和当前属性 getter 中使用 T。具体类可以实现已关闭的构造接口,如下所示:C# 复制代码
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:C# 复制代码
interface IBaseInterface1<T> { }
interface IBaseInterface2<T, U> { }class SampleClass1<T> : IBaseInterface1<T> { } //No error
class SampleClass2<T> : IBaseInterface2<T, string> { } //No error