数组,集合,IEnumerable接口,迭代器

发展:数组-->集合-->泛型

(1)数组

1. 数组数据结构是System.Array类的一个实例.

2. System.Array类的语法为

[SerializableAttribute]

[ComVisibleAttribute(true)]

public abstract class Array : ICloneable, IList, ICollection, IEnumerable

3. 下面看一个使用数组的例子(我称之为隐式实现)

protected void Page_Load(object sender, EventArgs e)

{

string[] strArrName = new string[3] { "Jim", "Andy", "Sun" };

foreach (string strName in strArrName)

{

lblName.Text += strName + ",";

}

}

或者这样写

protected void Page_Load(object sender, EventArgs e)

{

string[] strArrName = new string[3];

strArrName[0] = "Jim";

strArrName[1] = "Andy";

strArrName[2] = "Sun";

foreach (string strName in strArrName)

{

lblName.Text += strName + ",";

}

}

显示结果如下

Jim,Andy,Sun,

4. 下面看另一个使用数组的例子(我称之为显式实现)

protected void Page_Load(object sender, EventArgs e)

{

Array myArray = Array.CreateInstance(typeof(string), 3);

myArray.SetValue("Jim", 0);

myArray.SetValue("Andy", 1);

myArray.SetValue("Sun", 2);

foreach (string strName in myArray)

{

lblName.Text += strName + ",";

}

}

显示结果如下

Jim,Andy,Sun,

5. 优点:可以高效的访问给定下标的元素;System.Array类有自己的C#语法,使用它编程非常的直观.

6. 缺点:在实例化时必须指定数组的大小,以后也不能添加,插入,删除元素.

(2)集合

1. 针对数组数据结构的缺点,我们使用集合数据结构.

2. 集合数据结构中的类都位于System.Collections命名空间中.

3. 说到集合,我们必须先了解几个接口.想具体了解以下接口,可参考(3)集合接口

3.1 IEnumerable接口和IEnumerator接口

3.2 ICollection接口

public interface ICollection : IEnumerable

3.3 IList接口

public interface IList : ICollection, IEnumerable

3.4 IDictionary接口

public interface IDictionary : ICollection, IEnumerable

4. 说明一下:

4.1 ICollection接口是System.Collections命名空间中类的基接口.

4.2 ICollection接口扩展IEnumerable;IDictionary和IList则是扩展ICollection的更为专用的接口.IDictionary实现是键/值对的集合,如Hashtable类.IList实现是值的集合,其成员可通过索引访问,如ArrayList类.

4.3 某些集合(如Queue类和Stack类)限制对其元素的访问,它们直接实现ICollection接口.

4.4 如果IDictionary接口和IList接口都不能满足所需集合的要求,则从ICollection接口派生新集合类以提高灵活性.

(3)IEnumerable接口和IEnumerator接口

1. 我的理解:只有实现了IEnumerable接口的数据结构类才能使用foreach语句,下面给出例子

//Person类

public class Person

{

private string _firstName;

private string _lastName;

public string FirstName

{

get { return _firstName; }

}

public string LastName

{

get { return _lastName; }

}

public Person(string strFirstName, string strLastName)

{

this._firstName = strFirstName;

this._lastName = strLastName;

}

}

//PersonList集合,实现IEnumerable接口

public class PersonList : IEnumerable

{

private Person[] _arrPerson;

public PersonList(Person[] myArrPerson)

{

_arrPerson = new Person[myArrPerson.Length];

for (int i = 0; i < myArrPerson.Length; i++)

{

_arrPerson[i] = myArrPerson[i];

}

}

public IEnumerator GetEnumerator()

{

return new PeopleEnumerator(_arrPerson);

}

}

//实现IEnumerator接口

public class PeopleEnumerator : IEnumerator

{

private int _position = -1;

public Person[] _arrPerson;

public object Current

{

get

{

try

{

return _arrPerson[_position];

}

catch (IndexOutOfRangeException)

{

throw new InvalidOperationException();

}

}

}

public PeopleEnumerator(Person[] myArrPerson)

{

_arrPerson = myArrPerson;

}

public bool MoveNext()

{

_position++;

return (_position < _arrPerson.Length);

}

public void Reset()

{

_position = -1;

}

}

//集合的使用

protected void Page_Load(object sender, EventArgs e)

{

Person[] myArrPerson = new Person[3]

{

new Person("John", "Smith"),

new Person("Jim", "Johnson"),

new Person("Sue", "Rabon"),

};

PersonList myPersonList = new PersonList(myArrPerson);

foreach (Person myPerson in myPersonList)

{

lblName.Text += myPerson.FirstName + " " + myPerson.LastName + ",";

}

}

6. 说明一下我的理解,定义了一个集合类,实现IEnumerable接口,则必须定义一个与之相应的实现IEnumerator接口的类,这样是不是很麻烦呢?

(4)迭代器

1. 使用迭代器可避免上述麻烦,修改代码,注意橙色部分

public class Person

{

private string _firstName;

private string _lastName;

public string FirstName

{

get { return _firstName; }

}

public string LastName

{

get { return _lastName; }

}

public Person(string strFirstName, string strLastName)

{

this._firstName = strFirstName;

this._lastName = strLastName;

}

}

public class PersonList : IEnumerable

{

private Person[] _arrPerson;

public PersonList(Person[] myArrPerson)

{

_arrPerson = new Person[myArrPerson.Length];

for (int i = 0; i < myArrPerson.Length; i++)

{

_arrPerson[i] = myArrPerson[i];

}

}

public IEnumerator GetEnumerator()

{

//当编译器检测到迭代器时,它将自动生成IEnumerable或IEnumerable<T>接口的Current,MoveNext和Dispose方法.

for (int i = 0; i < _arrPerson.Length; i++)

{

yield return _arrPerson[i];

}

}

}

例子

实现IEnumerable接口的类可以进行简单迭代，例如foreach语句

using System;

using System.Collections.Generic;

using System.Text;

using System.Collections;

namespace IEnumerable接口

{

class Program

{

static void Main(string[] args)

{

A a = new A();

foreach (int? var in a)//当int值可能被赋空值时用？

{

Console.WriteLine(var);

}

}

}

class A : IEnumerable

{

int x = 1;

int y = 2;

int z = 3;

public IEnumerator GetEnumerator()

{

// int i = -1;

for (int i = 0; i <=3; i++)

{

if (i == x)

{

yield return 1;

}

else if (i == y)

{

yield return 2;

}

else if (i == z)

{

yield return 3;

}

else

{

yield return null;

}

}

}

}

}