Array类

创建数组

Array intArray1 = Array.CreateInstance(typeof(int), 5);

for (int i = 0; i < 5; i++)

{

intArray1.SetValue(33, i);

}

for (int i = 0; i < 5; i++)

{

Console.WriteLine(intArray1.GetValue(i));

}

Console.ReadKey();

分析:array类是一个抽象类,所以不能使用构造函数来创建数组(不能使用new).但除了可以使用C#语法创建数组实例之外,还可以使用静态方法CreateInstance()创建数组.如果事先不知道元素的类型,该静态方法就非常游泳.因为类型可以作为Type对象传递给CreateInstance()方法.

还可以将使用Array类创建的数组强制转换成声明为int[]的数组:

int[] intArray2 = (int[])intArray1;

CreateInstance()方法有许多重载版本,可以创建多维数组和不基于0的数组:

using System;

namespace ConsoleApplication4

{

class Program

{

static void Main(string[] args)

{

int[] lengths = { 2, 3 };

int[] lowerBounds = { 1, 10 };

Array racers = Array.CreateInstance(typeof(Person), lengths, lowerBounds);

racers.SetValue(new Person("a", "b"), 1, 10);

racers.SetValue(new Person("c", "d"), 1, 11);

racers.SetValue(new Person("e", "f"), 1, 12);

racers.SetValue(new Person("g", "h"), 2, 10);

racers.SetValue(new Person("i", "j"), 2, 11);

racers.SetValue(new Person("k", "l"), 2, 12);

Person[,] racers1 = (Person[,])racers;

Person first = racers1[1, 10];

}

}

public class Person

{

public Person()

{ }

public Person(string firstName, string lastName)

{

this.FirstName = firstName;

LastName = lastName;

}

public string FirstName { get; set; }

public string LastName { get; set; }

public override string ToString()

{

return String.Format("{0} {1}", FirstName, LastName);

}

}

}

使用SetValue()方法设置数组的元素,参数是:要设置的值,和当前索引号.

复制数组

因为数组是引用类型,所以江数组变量赋予另一个数组变量,就会得到两个引用同一数组的变量.而复制数组,会使数组实现ICloneable接口.这个接口定义的Clone()方法会创建数组的浅表副本.

如果数组的元素是值类型,则:

如果数组包含引用类型,则不复制元素,而知复制引用.

除了使用Clone()方法之外,还可以使用Array.Copy()方法创建浅表副本.但Clone()方法和Copy()方法有一个重要区别:Clone()方法会创建一个新数组,而Copy()方法必须传递阶数相同且有足够元素的已有数组.

如果需要包含引用类型的数组的深层副本,就必须迭代数组并创建对象.

排序

string[] names = {"zhao","qian","sun","li" };

Array.Sort(names);

foreach (var item in names)

{

Console.WriteLine(item);

}

Console.ReadKey();

排序后的结果:

li

qian

sun

zhao

由此看见,排序是按照字典序排列.

如果对数组使用自定义类,就必须事先IComparable接口.这个接口定义了一个方法CompareTo(),如果要比较的对象相等,该方法就返回0.如果该实例应拍在参数对象的前面,该方法就返回小于0的值.如果该实例应排在参数对象的后面,该方法就返回大于0的值.

案例:

public class Person:IComparable<Person>

{

public Person()

{ }

public Person(string firstName, string lastName)

{

this.FirstName = firstName;

LastName = lastName;

}

public string FirstName { get; set; }

public string LastName { get; set; }

public override string ToString()

{

return String.Format("{0} {1}", FirstName, LastName);

}

public int CompareTo(Person other)

{

if (other==null)

{

throw new ArgumentNullException("other");

}

int result = this.LastName.CompareTo(other.LastName);

if (result==0)

{

result = this.FirstName.CompareTo(other.FirstName);

}

return result;

}

}

编写测试代码:

static void Main(string[] args)

{

Person[] persons ={

new Person{FirstName="shan",LastName="yongxu"},

new Person{FirstName="sun",LastName="yanzhao"},

new Person{FirstName="zhu",LastName="haitao"},

new Person{FirstName="wang",LastName="jiwei"}

};

Array.Sort(persons);

foreach (var item in persons)

{

Console.WriteLine(item);

}

Console.ReadKey();

}

这样是按照名排序,不是按照姓排序.

如果Person对象的排序方式与上述不同,或者不能修改在数组中用作元素的类,就可以实现IComparer接口或IComparer<T>接口.这两个接口定义了方法Compare().要比较的类必须实现这两个接口之一.ICompare接口的Compare()方法定义了两个要比较的参数的原因.其返回值与IComparable接口的CompareTo()方法类似.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleApplication1

{

public enum PersonCompareType

{

FirstName,

LastName

}

public class PersonComparer : IComparer<Person>

{

private PersonCompareType compareType;

public PersonComparer(PersonCompareType compareType)

{

this.compareType = compareType;

}

public int Compare(Person x, Person y)

{

if (x==null||y==null)

{

throw new ArgumentNullException("x==y");

}

switch (compareType)

{

case PersonCompareType.FirstName:

return x.FirstName.CompareTo(y.FirstName);

case PersonCompareType.LastName:

return x.LastName.CompareTo(y.LastName);

default:

throw new ArgumentNullException("type");

}

}

}

class Program

{

static void Main(string[] args)

{

Person[] persons ={

new Person{FirstName="shan",LastName="yongxu"},

new Person{FirstName="sun",LastName="yanzhao"},

new Person{FirstName="zhu",LastName="haitao"},

new Person{FirstName="wang",LastName="jiwei"}

};

Array.Sort(persons,new PersonComparer(PersonCompareType.FirstName));

foreach (var item in persons)

{

Console.WriteLine(item);

}

Console.ReadKey();

}

}

public class Person : IComparable<Person>

{

public Person()

{ }

public Person(string firstName, string lastName)

{

this.FirstName = firstName;

LastName = lastName;

}

public string FirstName { get; set; }

public string LastName { get; set; }

public override string ToString()

{

return String.Format("{0} {1}", FirstName, LastName);

}

public int CompareTo(Person other)

{

if (other == null)

{

throw new ArgumentNullException("other");

}

int result = this.LastName.CompareTo(other.LastName);

if (result == 0)

{

result = this.FirstName.CompareTo(other.FirstName);

}

return result;

}

}

}

分析:类PersonComparer实现了IComparer<Person>接口,可以按照FirstName或LastName对象排序.枚举PersonComparerType定义了可用于PersonComparer的排序选项:FirstName和LastName.排序方式由PersonComparer类的构造函数定义,在该构造函数中设置了一个PersonComparerType值.实现Compare()方法时用一个switch语句指定是按照FirstName还是LastName排序.

这样就可以按照你的需要来排序;是按照姓排序,还是按照名排序?

Array类还提供了Sort方法,需要将一个委托作为参数,这个参数可以传递给方法,从而比较两个对象,而不需要依赖IComparable或IComparer接口.