【转载】今天心情非常好,再发一组 Linq、集合、数组、Lambda、QuerySyntax 的文章

基于System.Array定义数组

System.Array x=System.Array.CreateInstance( typeof ( string ),7);

x.SetValue("4",0);

x.SetValue("8",1);

x.SetValue("7",2);

x.SetValue("1",3);

x.SetValue("3",4);

x.SetValue("2",5);

x.SetValue("5",6);

System.Console.WriteLine(x.GetValue(5));

System.Collections.Generic. List <System.Windows.Forms. TextBox > jh = new List < TextBox >();

jh.Add( new TextBox ());

int i = 100;

foreach (System.Windows.Forms. TextBox tp in jh)

i = i + 100;

tp.Text =i.ToString();

tp.Left = i;

this .Controls.Add(tp);

System.Collections.Generic. List < a > jh = new List < a >();

jh.Add( new a ( "123" ));

jh.Add( new a ( "456" ));

jh.Add( new a ( "789" ));

foreach ( a tp in jh)

System. Console .WriteLine(tp.s);

System. Converter < TInput,TOutput >

public delegate TOutput Converter <TInput, TOutput>(TInput input);

将对象从一种类型转换为另一种类型的方法

public static void Main()

List < string > ls = new List < string >() { "1" , "2" , "3" };

//System.Converter<string, int> cw=new Converter<string,int>(stringToint);

//List<int> li = ls.ConvertAll<int>(cw);

List < int > li= ls.ConvertAll< int >(stringToint);

public static int stringToint( string s)

return int .Parse(s);

List < string > ls = new List < string >() { "1" , "2" , "3" };

// System.Collections.Generic.IEnumerable<int> li = ls.Select(i => int.Parse(i)); ;

var li = ls.Select(i=> int .Parse(i));

static void Main( string [] args)

List < string > ls = new List < string >() { "1" , "2" , "3" };

List < string > li = ls.ConvertAll< string >(stringAdd);

public static string stringAdd( string s)

return s+ "wxd" ;

static void Main( string [] args)

List < string > ls = new List < string >{ "wxd" , "lzm" };

// System.Action<string> w = new System.Action<string>(wxdPrint);

// ls.ForEach(w);

ls.ForEach(wxdPrint);

static void wxdPrint( string s)

Console .WriteLine(s);

Find、FindLast、FindIndex、FindLastIndex、Exists、TrueForAll

public T Find ( Predicate <T> match)

检索与条件匹配的所有元素，并返回整个 List 中的第一个匹配元素，其中包含与指定谓词所定义的条件相匹配的所有元素；否则为一个空 List

FindLast 返回索引值 public T FindLast ( Predicate <T> match)

FindIndex 返回索引值 public int FindIndex ( Predicate <T> match)

FindLastIndex 返回逻辑型 public int FindLastIndex ( Predicate <T> match)

Exists 返回逻辑型 public bool Exists ( Predicate <T> match)

TrueForAll 返回逻辑型，确定是否 List 中的每个元素都与指定的谓词所定义的条件相匹配 public bool TrueForAll ( Predicate <T> match)

List < int > ls = new List < int >() { 1, 2, 3 };

//System.Predicate<int> cw = new Predicate<int>(wxdFind);

// int a = ls.Find(cw);

int a = ls.Find(wxdFind);

public static bool wxdFind( int v)

bool b = (v >= 2); // 查找条件

return b;

FindAll

public List <T> FindAll ( Predicate <T> match)

检索与条件匹配的所有元素，如果找到，则为一个 List，其中包含与指定谓词所定义的条件相匹配的所有元素；否则为一个空 List

List < int > ls = new List < int >() { 1, 2, 3 };

// System.Predicate<int> cw = new Predicate<int>(WxdFind);

//List<int> li = ls.FindAll(cw);

List < int > li = ls.FindAll(WxdFind);

public static bool WxdFind( int v)

bool b = (v <= 2); // 查找条件

return b;

//以视图形式，不创建复本

List < int > ls = new List < int >() { 1, 2, 3 ,4,5};

//System.Collections.Generic.IEnumerable<int> li = ls.Where(i => i < 3);

var li = ls.Where(i => i < 3);

List < int > ls = new List < int >() { 1,2, 2, 3,4,5 };

//System.Predicate<int> cw = new Predicate<int>(WxdRem);

//int n = ls.RemoveAll(cw);

int n = ls.RemoveAll(WxdRem); //n为移除的个数

public static bool WxdRem( int v)

bool b = (v <= 2); // 条件

return b;

List < int > ls = new List < int >{1,3,2,4,5,0,8,1};

// System.Comparison<int> w = new Comparison<int>(wxdSort);

// ls.Sort(w);

ls.Sort(wxdSort);

static int wxdSort( int x, int y)

int v = x - y;

return v;

//return -v; //升序

//不改变原集合的顺序

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

//System.Collections.Generic.IEnumerable<int> li = ls.OrderBy(i => i);

var li = ls.OrderBy(i => i);

System.Collections

System.Collections.DictionaryEntry 结构字典键/值对

散列表（也叫哈希表），是根据关键码值直接进行访问的数据结构，也就是说，它通过把关键码值映射到表中一个位置来访问记录，以加快查找的速度。这个映射函数叫做散列函数，存放记录的数组叫做散列表。

哈希表使用的是链式存储

哈希表使用键值对的方式来存储

哈希表中，键名不能重复

foreach ( object zd in x)

{ System.Collections.DictionaryEntry obj =(DictionaryEntry)zd;

System.Console.WriteLine(obj.Key);

System.Console.WriteLine(obj.Value);

System.Collections.Generic. SortedList < a , System.Windows.Forms. TextBox > jh= new SortedList < a , TextBox >();

a k1 = new a ( "123" ,0);

a k2 = new a ( "456" ,100);

a k3 = new a ( "789" ,200);

jh.Add(k1, new TextBox ());

jh.Add(k2, new TextBox ());

jh.Add(k3, new TextBox ());

//值操作

foreach ( TextBox tp in jh.Values)

this .Controls.Add(tp);

//键操作

foreach ( a tp in jh.Keys)

tp.s = "ok" ;

//键值对操作

foreach (System.Collections.Generic. KeyValuePair < a , TextBox > tp in jh)

tp.Value.Text = tp.Key.s;

tp.Value.Left = tp.Key.l;

//通过键操作值

jh[k2].Text = "hello" ;

System.Collections.Generic. LinkedList < a > lb = new LinkedList < a >();

System.Collections.Generic. LinkedListNode < a > p;

void 添加结点()

p = new LinkedListNode < a >( new a ( "1" ));

lb.AddFirst(p);

lb.AddAfter(lb.First, new a ( "2" ));

lb.AddBefore(lb.First, new a ( "3" ));

lb.AddLast( new a ( "4" ));

lb.AddFirst( new a ( "5" ));

void 读取头尾结点()

string fs = lb.First.Value.s;

string ls = lb.Last.Value.s;

System. Console .WriteLine(fs +ls);

void 下一节点( object sender, EventArgs e)

p = p.Next;

if (p == null )

System. Console .WriteLine( "到达边界" );

System. Console .WriteLine(p.Value.s);

void 上一结点()

p = p.Previous;

if (p == null )

System. Console .WriteLine( "到达边界" );

System. Console .WriteLine(p.Value.s);

static void Main( string [] args)

System.Linq.Expressions. Expression < lzm < int , bool >> ep;

ep = le => le > 123;

public class 集合 : System.Collections. CollectionBase , System.Collections. IEnumerable

//属性访问器

成员 this [ int index]

get { return ( 成员 )List[index] ; }

//添加成员

public int Add( 成员 v)

{ return List.Add(v);}

//实现GetEnumerator接口

public new System.Collections. IEnumerator GetEnumerator()

迭代器 d = new 迭代器 ( this );

return d;

//--------以下为迭代器类-------------

//迭代器子类

public class 迭代器 : System.Collections. IEnumerator

int index = -1; //索引用

集合 jh;

public 迭代器( 集合 v) //构造函数

{ jh = v; }

public void Reset() //重新初始化索引

{index = -1;}

public object Current //返回当前索引所指的对象

get { return jh.List[index];}

public bool MoveNext() //将索引指针向下移动一位

if (index < jh.List.Count-1)

index = index + 1;

return true ;

return false ;

//--------以下为成员类-------------

//迭代器中的数据成员

public class 成员

{ public string a;}

//第一种方法：显示使用

System.Collections. IEnumerator ee = j.GetEnumerator();

while (ee.MoveNext())

集合 . 成员 temp = ( 集合 . 成员 )ee.Current;

System. Console .WriteLine(temp.a );

//第二种方法：隐式使用

foreach ( 集合 . 成员 bb in j)

System. Console .WriteLine(bb.a);

public class wxd : System.Collections. IEnumerable

string [] v = { "a" , "b" , "c" , "d" , "e" , "f" , "g" };

public System.Collections. IEnumerator GetEnumerator()

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

yield return v[i];

yield return "wxd" ;

yield return "lzm" ;

//第一种方法：显示使用

System.Collections. IEnumerator ee = x.GetEnumerator();

while (ee.MoveNext())

string temp = ( string )ee.Current;

System. Console .WriteLine(temp);

//第二种方法：隐式使用

foreach ( string v in x)

System. Console .WriteLine(v);

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

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。

static void Main( string [] args)

ArrayList ls = new ArrayList () { new wxd { value = 4 }, new wxd { value = 2 }, new wxd { value = 1 }, new wxd { value = 3 } };

ls.Sort( new wxd ());

class wxd : System.Collections. IComparer

public int value;

public int Compare( object x, object y)

int v = (( wxd )x).value - (( wxd )y).value;

return v;

static void Main( string [] args)

List < wxd > ls = new List < wxd > { new wxd { value = 4 }, new wxd { value = 2 }, new wxd { value = 1 }, new wxd { value = 3 } };

ls.Sort( new wxd ());

class wxd : System.Collections.Generic. Comparer < wxd >

public int value;

public override int Compare( wxd x, wxd y)

int v = x.value - y.value;

return v;

public int ID { get ; set ; }

public string Name { get ; set ; }

public static void Main()

List < a > list = new List < a > { new a { ID = 1, Name = "wxd" }, new a { ID = 2, Name = "lzm" }, new a { ID = 3, Name = "wxwinter" } };

var l1 = list.WxdWhere(le => le.Name == "lzm" );

// 上面的（Lambda表达式）等同于下面的（匿名方法）

IEnumerable < a > l2 = list.WxdWhere( delegate ( a le) { return le.Name == "lzm" ; });

//与调用系统Where一样

var l3 = list.Where(le => le.Name == "lzm" );

public static class e

// 相关委托

public delegate TResult Func <T, TResult>(T arg);

//相关Where扩展方法

//Func<TSource, bool>：接受一个类型为TSource的参数

//Func<TSource, bool>：某个需要满足的条件，返回bool值

public static IEnumerable <TSource> WxdWhere<TSource>( this IEnumerable <TSource> source, Func <TSource, bool > predicate)

foreach (TSource item in source)

if (predicate(item))

yield return item;

List < string > ls = new List < string >() { "1" , "2" , "3" };

// System.Collections.Generic.IEnumerable<int> li = ls.Select(i => int.Parse(i)); ;

var li = ls.Select(i=> int .Parse(i));

static void Main( string [] args)

List < string > ls = new List < string >() { "1" , "2" , "3" };

var li = ls.Select< string , string >(stringAdd);

public static string stringAdd( string s)

return s+ "wxd" ;

List < string > ls = new List < string >() { "wxd/1" , "lzm/2" , "wxwinter/3" };

var li = ls.SelectMany(p => p.Split( '/' ));

foreach ( var s in li)

Console .WriteLine(s);

List < int > ls = new List < int >() { 1, 2, 3, 4, 5 };

var li = ls.Where(i => i < 3); //li中此时只有1,2

ls[0] = 333; //1已改为333，li中此时只有2

//以视图形式，不创建复本

List < int > ls = new List < int >() { 1, 2, 3 ,4,5};

//System.Collections.Generic.IEnumerable<int> li = ls.Where(i => i < 3);

var li = ls.Where(i => i < 3);

List < int > ls = new List < int >() { 1, 2, 3, 4, 5 };

// System.Func<int, bool> ww = new Func<int, bool>(w);

// var li = ls.Where(ww);

var li = ls.Where(w);

public static bool w( int v)

return v<3;

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

var li = ls.OrderBy(i => i);

//----

ls[1] = 6666;

ls.Add(-5);

//---li中的顺序已重新排列

//不改变原集合的顺序

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

//System.Collections.Generic.IEnumerable<int> li = ls.OrderBy(i => i);

var li = ls.OrderBy(i => i);

static void Main( string [] args)

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

var li = ls.OrderBy< int , int >(w );

public static int w( int i)

return -i; //降序

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

//var li = ls.OrderBy<int, int>(delegate(int i) { return -i; });

var li = ls.OrderBy( delegate ( int i) { return -i; })

string [] wxd = { "Java" , "C#" , "C++" , "Delphi" , "VB.net" , "VC.net" , "C++ Builder" , "Kylix" , "Perl" , "Python" };

var query = wxd.GroupBy(p => p.Length);

foreach ( var item in query)

Console .WriteLine( "长度 {0}" , item.Key);

foreach ( var val in item)

Console .WriteLine(val);

string [] wxd = { "Java" , "C#" , "C++" , "Delphi" , "VB.net" , "VC.net" , "C++ Builder" , "Kylix" , "Perl" , "Python" };

var query = from item in wxd

group item by item.Length into lengthGroups

select lengthGroups;

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 3 } };

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

//返回一个新的匿名类的集合

var li=ls1.Join(ls2,temp1=>temp1.Name,temp2=>temp2.ID,(temp1,temp2)=> new { temp1.Name, temp1.Value, temp2.ID, temp2.bak });

foreach ( var s in li)

Console .WriteLine( "{0}-{1}-{2}-{3}" , s.Name, s.ID, s.Value, s.bak);

public class T1

public string Name;

public int Value;

public class T2

public string ID;

public string bak;

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 3 } };

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

//返回一个新的匿名类的集合

var li = ls1.GroupJoin(ls2, temp1 => temp1.Name, temp2 => temp2.ID, (temp1, temp2) => new { temp1.Name, temp1.Value, 个数 = temp2.Count() });

foreach ( var s in li)

Console .WriteLine( "Name :{0},共有:{1}" ,s.Name,s.个数.ToString());

public class T1

public string Name;

public int Value;

public class T2

public string ID;

public string bak;

//返回一个新的匿名类的集合

var li = from temp1 in ls1

join temp2 in ls2 on temp1.Name equals temp2.ID

into newtab

select new { temp1.Name, temp1.Value, 个数 = newtab.Count() };

List < int > ls = new List < int >() { 1, 3, 2, 4, 5, 0, 8, 1 };

var li = ls.Take(5); //li[1, 3, 2, 4, 5]

ls.Insert(0, 999); //li[999,1, 3, 2, 4]

List < int > ls1 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1 };

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,100,200,100,300 };

var li = ls1.Union(ls2);

List < int > ls1 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1 };

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,100,200,100,300 };

var li = ls1.Concat(ls2);

List < int > ls1 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,50 };

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,100,200,100,300 };

var li = ls1.Intersect(ls2);

List < int > ls1 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,50 };

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1,100,200,100,300 };

var li = ls1.Except(ls2);

ArrayList ls1 = new ArrayList { "a" , "b" , "1" };

// ArrayList ls1 = new ArrayList { "a", "b", 1 }; //下面的转换会报错

// List<string > ls2 = (List<string >)ls1; //编译会报错

// List<string> ls3 = (List<string>)ls1.Cast<string>(); //运行会报错

var ls4 = ls1.Cast< string >();

List < string > ls5 = ls1.Cast< string >().ToList< string >();

ArrayList ls1 = new ArrayList { "a" , "b" , "c" ,1 };

var ls4 = ls1.OfType< string >().Cast< string >();

ls1[0] = 345;

foreach ( object s in ls4)

System. Console .WriteLine(s);

List < int > ls = new List < int >() { 1, 3, 2, 2, 5, 2, 8 };

var o = ls.FirstOrDefault(); //第一个

var o1 = ls.FirstOrDefault(p => p > 2); //第一个大于2的

List < int > ls = new List < int >() { 1, 3, 2, 2, 5, 2, 8,1 };

var o = ls.LastOrDefault(); //最后一个

var o1 = ls.LastOrDefault(p => p > 2); //最后一个大于2的

static void Main( string [] args)

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

T2 obj = new T2 () { bak = "sss" , ID = "ok" };

ls2.Add(obj);

bool b = ls2.Contains(obj); //true 更多肉容见对像比效

public class T2

public string ID;

public string bak;

static void Main( string [] args)

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

bool b1 = ls2.Any(p => p.bak.Contains( "ell" ) ); //true

bool b2 = ls2.Any(p => p.ID== "a" ); //true

public class T2

public string ID;

public string bak;

static void Main( string [] args)

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

bool b1 = ls2.All(p => p.bak.Contains( "e" ) ); //false

bool b2 = ls2.All(p => p.ID.Length ==1 ); //true

public class T2

public string ID;

public string bak;

List < int > ls1 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1 };

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1 };

bool b1 = ls2.SequenceEqual(ls1); //true

List < int > ls2 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 1 };

int b1 = ls2.Count(p => p < 3); //5

int b2 = ls2.Count(); //8

List < int > ls3 = new List < int >() { 1, 3, 2, 2, 5, 2, 8, 2 };

var b1 = ls3.Average(); //3.125

var b2 = ls3.Sum(); //25

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 4 } };

var b1 = ls1.Average(p=>p.Value); //2.33333333333333

var b2 = ls1.Sum(p=>p.Value); //7

public class T1

public string Name;

public int Value;

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 4 } };

var b1 = ls1.Min(p=>p.Value); //1

var b2 = ls1.Max(p=>p.Value); //4

public class T1

public string Name;

public int Value;

List < int > ls3 = new List < int >() { 1, 2, 3, 4, 5, 6, 7, 8, 9,10 };

var b1 = ls3.Aggregate((x, y) => x + y ); //55 累加

var b2 = ls3.Aggregate((x, y) => x * y); //3628800 累乘

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 4 } };

var b3 = ls1.Aggregate< T1 >((x, y) => new T1 { Value = x.Value + y.Value });

System. Console .WriteLine(b3.Value); //7

public class T1

public string Name;

public int Value;

List < string > ls3 = new List < string >() { "wxd" , "lzm" , "wxwinter" , "wxd" };

var ls4 = ls3.Where(p => p == "ok" ).DefaultIfEmpty( "not" ); ;

//如果不存在返回给集合一个自定义的对象

List < string > ls3 = new List < string >() { "wxd" , "lzm" , "wxwinter" , "wxd" };

List < string > ss = ls3.ToList();

ls3[0] = "kk" ; //不影响 ss 集合

List < string > ls3 = new List < string >() { "wxd" , "lzm" , "wxwinter" , "wxd" };

var ss = ls3.Select(p=>p);

ls3[0] = "kk" ; //影响 ss 集合

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 4 } };

System.Collections.Generic. Dictionary < string , T1 > dd = ls1.ToDictionary(p => p.Name);

var d = ls1.ToDictionary(p => p.Name); //如果集合中有值相同的Name,将报错

//指定对象为键，原集合中的对象为值

foreach ( var s in dd)

System. Console .WriteLine(s);

public class T1

public string Name;

public int Value;

public int ID { get ; set ; }

public string Name { get ; set ; }

public static void Main()

List < a > list = new List < a > { new a { ID = 1, Name = "wxd" }, new a { ID = 2, Name = "lzm" }, new a { ID = 3, Name = "wxwinter" } };

var l1 = list.WxdWhere(le => le.Name == "lzm" );

// 上面的（Lambda表达式）等同于下面的（匿名方法）

IEnumerable < a > l2 = list.WxdWhere( delegate ( a le) { return le.Name == "lzm" ; });

//与调用系统Where一样

var l3 = list.Where(le => le.Name == "lzm" );

public static class e

// 相关委托

public delegate TResult Func <T, TResult>(T arg);

//相关Where扩展方法

//Func<TSource, bool>：接受一个类型为TSource的参数

//Func<TSource, bool>：某个需要满足的条件，返回bool值

public static IEnumerable <TSource> WxdWhere<TSource>( this IEnumerable <TSource> source, Func <TSource, bool > predicate)

foreach (TSource item in source)

if (predicate(item))

yield return item;

//int temp = i;

// list.Add(() => temp); // 1,2,3 这个temp，就称为lifting。lift是美语中的电梯，翻译为梯子或垫脚石，比较妥帖

list.Add(() => i); //3,3,3

foreach ( var item in list)

Console .WriteLine(item());

所盼望输出，0，1，2，而实际结果是3,3,3。

两个原因。

第一，在for循环中，只能有一个 i 变量。即再第一次循环时，i 的地址就分配好了，不会因为循环次数的多少而发生任何改变，其改变的只能是里面装载的值。

第二，lambda表达式在构造时，传进去的是变量的地址，而不是具体值。只有当真正执行这个lambda表达式时，才会去确定它的值。这就是为什么上面的例子中，其结果均为3。（for循环在最后，又给 i 加了1）

在for循环中，定义一临时变量temp存储 i的值即可。因为编译器会对该临时变量重新分配内存，这样，每次循环，都重新分配新的内存，就不会有这个问题

static void Main( string [] args)

List < T > ls = new List < T > { new T { Name = "a" , Value = 1 }, new T { Name = "b" , Value = 2 }, new T { Name = "c" , Value = 3 }, };

var l1 = from temp in ls select temp;

var l2 = from temp in ls select "姓名:" + temp.Name ;

var l3 = from temp in ls where temp.Value <= 2 select temp;

System.Collections. IEnumerable l4 = from temp in ls where temp.Value <= 2 select temp;

System.Collections.Generic. IEnumerable < T > l5 = from temp in ls where temp.Value <= 2 select temp;

public class T

public string Name;

public int Value;

static void Main( string [] args)

List < T > ls = new List < T > { new T { Name = "a" , Value = 1 }, new T { Name = "b" , Value = 2 }, new T { Name = "c" , Value = 3 }, };

var l3 = from temp in ls select new T2 { x=temp.Name , y=temp.Value , z=000};

foreach ( var s in l3)

{ Console .WriteLine(s.x + s.y + s.z); }

ls[0].Name = "wxd" ;

foreach ( var s in l3)

{ Console .WriteLine(s.x + s.y + s.z);}

System. Console .Read();

public class T

public string Name;

public int Value;

public class T2

public string x;

public int y;

public int z;

List < int > ls = new List < int >() { 1, 2, 3, 4, 5 };

// var l3 = (from temp in ls select temp);

var l3 = ( from temp in ls select temp).ToList() ;

static void Main( string [] args)

List < T > ls = new List < T > { new T { Name = "a" , Value = 1 }, new T { Name = "b" , Value = 2 }, new T { Name = "c" , Value = 3 }, };

List < int > li = new List < int > {1,2 };

var l1 = from temp1 in ls

from temp2 in li

where temp1.Value == temp2

select new { temp1.Name, v = temp2 * 100 }; //返回一个新的匿名类的集合

public class T

public string Name;

public int Value;

static void Main( string [] args)

List < T > ls = new List < T > { new T { Name = "a" , Value = 1 }, new T { Name = "b" , Value = 2 }, new T { Name = "c" , Value = 3 }, };

var l1 = ( from temp in ls orderby temp.Value, temp.Name select temp);

var l2 = ( from temp in ls orderby temp.Value descending select temp);

var l3 = ( from temp in ls where temp.Value < 5 orderby temp.Value ascending select temp);

var l4 = ( from temp in ls orderby temp.Value ascending where temp.Value < 5 select temp);

public class T

public string Name;

public int Value;

static void Main( string [] args)

List < T > ls = new List < T > { new T { Name = "a" , Value = 1 }, new T { Name = "b" , Value = 2 }, new T { Name = "c" , Value = 3 }, new T { Name = "d" , Value = 1 }, new T { Name = "e" , Value = 3 } };

var l1 = from temp in ls

group temp by temp.Value into gp

select gp;

var l2 = from temp in ls

orderby temp.Name descending //对ls的结果集合排序

group temp by temp.Value into gp

orderby gp.Key descending //对组集合排序

select gp;

System.Collections.Generic. IEnumerable <System.Linq. IGrouping < int , T >> l3 = from temp in ls

group temp by temp.Value into gp

select gp;

foreach ( var s in l2)

Console .WriteLine( "{0}组" ,s.Key);

foreach ( var ss in s)

Console .WriteLine(ss.Name);

public class T

public string Name;

public int Value;

string [] wxd = { "Java" , "C#" , "C++" , "Delphi" , "VB.net" , "VC.net" , "C++ Builder" , "Kylix" , "Perl" , "Python" };

var query = from item in wxd

orderby item

group item by item.Length into lengthGroups

orderby lengthGroups.Key descending

select lengthGroups;

foreach ( var item in query)

Console .WriteLine( "长度 {0}" , item.Key);

foreach ( var val in item)

Console .WriteLine(val);

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 3 } };

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

//返回一个新的匿名类的集合

var li = from temp1 in ls1 join temp2 in ls2 on temp1.Name equals temp2.ID select new { temp1.Name, temp1.Value, temp2.ID, temp2.bak };

foreach ( var s in li)

Console .WriteLine( "{0}-{1}-{2}-{3}" ,s.Name,s.ID,s.Value,s.bak);

public class T1

public string Name;

public int Value;

public class T2

public string ID;

public string bak;

static void Main( string [] args)

List < T1 > ls1 = new List < T1 > { new T1 { Name = "a" , Value = 1 }, new T1 { Name = "b" , Value = 2 }, new T1 { Name = "c" , Value = 3 } };

List < T2 > ls2 = new List < T2 > { new T2 { ID = "a" , bak = "hello" }, new T2 { ID = "a" , bak = "wxwinter" }, new T2 { ID = "c" , bak = "lzm" }, };

//返回一个新的匿名类的集合

var li = from temp1 in ls1

join temp2 in ls2 on temp1.Name equals temp2.ID

into newtab

select new { temp1.Name, temp1.Value, 个数 = newtab.Count() };

foreach ( var s in li)

Console .WriteLine( "Name :{0},共有:{1}" ,s.Name,s.个数.ToString());

public class T1

public string Name;

public int Value;

public class T2

public string ID;

public string bak;

winform

List < aa > ls = new List < aa > { new aa { a = "a" , b = "1" }, new aa { a = "b" , b = "2" } };

dataGridView1.DataSource = ls; //数据修改会与集合同步

//两个控件指针会同步

comboBox1.DataSource = ls;

comboBox1.DisplayMember = "b" ;

protected void Button1_Click( object sender, EventArgs e)

List < aa > ls = new List < aa > { new aa { a = "a" , b = "1" }, new aa { a = "b" , b = "2" } };

this .GridView1.DataSource = ls;

DropDownList1.DataSource = ls;

DropDownList1.DataTextField = "b" ;

DropDownList1.DataValueField = "a" ;

this .DataBind();