C#高级特性_Lambda

“Lambda 表达式”(lambda expression)是一个匿名函数

省略delegate，甚至省略参数类型；

直接用（参数）=> {语句或表达式}

例如：

button1.Click += (sender, e) =>{......}

new Thread  ( () => {......} ). Start();

PlotFun ( x => x*x, 0, 100 );

lambda特点：

lambda表达式比匿名函数简单，不写参数的匿名函数可以转化成任意多个参数的委托。

使用示例：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

using System.Threading;

namespace MethodDelegateLamda
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //示例1,使用线程
        private void button1_Click(object sender, EventArgs e)
        {
            //csharp 1.0
            //使用委托，使用已定义好的函数
            new Thread(new ThreadStart(MyFun)).Start();

            //csharp 2.0
            //省略委托：MyFun自动实例化为ThreadStart委托（
            new Thread(MyFun).Start();
            //匿名方法
            new Thread(new ThreadStart( delegate(){ Console.Write("my function"); })).Start();
            //匿名方法，省略参数列表
            new Thread(new ThreadStart( delegate{ Console.Write("my function"); })).Start();
            //匿名方法，自动转委托
            new Thread( delegate(){ Console.Write("my function"); }).Start(); 

            //csharp 3.0
            //Lambda表达式
            new Thread(() => { Console.Write("my function"); }).Start();

        }

        void MyFun()
        {
            Console.Write("my function");
        }

        //示例2,使用事件

        private void button3_Click(object sender, EventArgs e)
        {
            Example3();
        }
        void Example3()
        {
            //csharp 1.0
            //使用委托，使用自定义函数
            this.MouseMove += new MouseEventHandler(Form1_MouseMove);

            //csharp 2.0
            //自动转委托
            this.MouseMove += Form1_MouseMove; 

            Label lbl = this.label1; //这个变量下面使用了闭包（简单地说，使用外部的局部变量）
            this.MouseMove += new MouseEventHandler(delegate(object sender, MouseEventArgs e) { lbl.Text = e.X + "," + e.Y; });
            this.MouseMove += delegate(object sender, MouseEventArgs e) { lbl.Text = e.X + "," + e.Y; };

            //csharp 3.0
            //使用Lambda表达式
            this.MouseMove += (object sender, MouseEventArgs e) => { lbl.Text = e.X + "," + e.Y; };　//Lamda
            this.MouseMove += (sender, e) => { lbl.Text = e.X + "," + e.Y; }; //可以省略类型
        }

        void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            this.label1.Text = e.X + "," + e.Y;
        }

        //示例3, 数组排序
        class Book
        {
            public string title;
            public double price;
            public Book(string title, double price) { this.title=title; this.price=price; }
        }
        private void button2_Click(object sender, EventArgs e)
        {
            Random rnd = new Random();
            Book [] books  = new Book[ 10];
            for( int i=0; i<books.Length; i++ ) books[i] = new Book( "Book"+i, rnd.Next(100) );

            //csharp 1.0
            Array.Sort(books, new MyComparer()); //用一个IComparer

            //csharp 2.0
            Array.Sort<Book>(books, new Comparison<Book>(delegate(Book book1, Book book2) { return (int)(book1.price - book2.price); })); //使用Comparison委托
            Array.Sort<Book>(books, delegate(Book book1, Book book2) { return (int)(book1.price - book2.price); });

            //csharp 3.0
            Array.Sort<Book>(books, (Book book1, Book book2) => (int)(book1.price - book2.price));
            Array.Sort<Book>(books, (book1, book2) => (int)(book1.price - book2.price)); //省略参数类型

            //使用Linq
            IOrderedEnumerable<Book> result = from book in books orderby book.price select book;

            var result2 = from book in books  where book.price>=0 orderby book.price select book.title;
            foreach (string s in result2) Console.Write(s);

            var result3 = books
                .Where<Book>(b => b.price>=0)
                .OrderBy<Book, double>(b => b.price, Comparer<double>.Default)
                .Select<Book,Book>(book => book);
            foreach (Book b in result3) Console.Write(b.price+" ");
       }

        class MyComparer : System.Collections.IComparer
        {
            public int Compare(object x1, object x2)
            {
                return (int)(((Book)x1).price - ((Book)x2).price);
            }
        }
    }
}