C#基础知识---Lambda表达式
一、Lambda表达式简介
Lambda表达式可以理解为匿名函数，可以包含表达式和语句。它提供了一种便利的形式来创建委托。
Lambda表达式使用这个运算符--- “=>”，它读成“goes to” ,该运算符的左边为输入参数，右边是表达式或者语句块。
二、例子
例1：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Lambda
{
class Program
{
static void Main(string[] args)
{
//下面是C# 1中创建委托实例的代码
Func<string, int> del1 = new Func<string, int>(CallBackMethod);
//C#2中用匿名方法来创建委托实例，CallBackMethod
Func<string, int> del2 = delegate (string text)
{
return text.Length;
};
//C# 3中使用Lambda表达式来创建委托实例
Func<string, int> del3 = (string text) => text.Length;
// 可以省略参数类型string,把上面代码再简化为：
Func<string, int> del4 = (text) => text.Length;
// 如果Lambda表达式只需一个参数，并且那个参数可以隐式指定类型时，
// 此时可以把圆括号也省略,简化为：
Func<string, int> del5 = text => text.Length;
int length = del5("Test");
Console.WriteLine("Length:" + length);
Console.ReadKey();
}
private static int CallBackMethod(string str)
{
return str.Length;
}
}
}
1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4 using System.Text;
5 using System.Threading.Tasks;
6 using System.Windows.Forms;
7
8 namespace Lambda
9 {
10 class Program
11 {
12 static void Main(string[] args)
13 {
14
15 //下面是C# 1中创建委托实例的代码
16 Func<string, int> del1 = new Func<string, int>(CallBackMethod);
17
18 //C#2中用匿名方法来创建委托实例，CallBackMethod
19 Func<string, int> del2 = delegate (string text)
20 {
21 return text.Length;
22 };
23
24 //C# 3中使用Lambda表达式来创建委托实例
25 Func<string, int> del3 = (string text) => text.Length;
26
27 // 可以省略参数类型string,把上面代码再简化为：
28 Func<string, int> del4 = (text) => text.Length;
29
30 // 如果Lambda表达式只需一个参数，并且那个参数可以隐式指定类型时，
31 // 此时可以把圆括号也省略,简化为：
32 Func<string, int> del5 = text => text.Length;
33
34 int length = del5("Test");
35 Console.WriteLine("Length:" + length);
36
37 Console.ReadKey();
38 }
39
40 private static int CallBackMethod(string str)
41 {
42 return str.Length;
43 }
44 }
45 }
例2：
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace Lambda
{
class Program
{
static void Main(string[] args)
{
Button button1 = new Button() { Text = "按钮1", Width = 50, Height = 50, Name = "button1" };
button1.Left = 10;
button1.BackColor = System.Drawing.Color.Red;
Button button2 = new Button() { Text = "按钮二", Width = 50, Height = 50, Left = 70, Name = "button2" };
button2.BackColor = System.Drawing.Color.Green;
// C# 2中使用匿名方法来订阅事件
button1.Click += delegate (object sender, EventArgs e)
{
ReportEvent("Click事件", sender, e);
};
// C# 3Lambda表达式方式来订阅事件
button2.Click += (sender, e) => ReportEvent("Click事件", sender, e);
Form form = new Form { Name = "在控制台中创建的窗体", AutoSize = true };
form.Controls.Add(button1);
form.Controls.Add(button2);
// 运行窗体
string str = "";
bool isShow = false;
while (!isShow)
{
str = Console.ReadLine();
switch (str)
{
case "show":
isShow = true;
Application.Run(form);
break;
case "quit":
Environment.Exit(0);
break;
}
}
Console.ReadKey();
}
// 记录事件的回调方法
private static void ReportEvent(string title, object sender, EventArgs e)
{
Console.WriteLine("事件名称：{0}", title);
Console.WriteLine("激发事件的对象：{0}", (sender as Button).Name);
Console.WriteLine("事件参数类型： {0}", e.GetType());
Console.WriteLine();
Console.WriteLine();
}
}
}
1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4 using System.Text;
5 using System.Threading.Tasks;
6 using System.Windows.Forms;
7
8 namespace Lambda
9 {
10 class Program
11 {
12 static void Main(string[] args)
13 {
14 Button button1 = new Button() { Text = "按钮1", Width = 50, Height = 50, Name = "button1" };
15 button1.Left = 10;
16 button1.BackColor = System.Drawing.Color.Red;
17
18 Button button2 = new Button() { Text = "按钮二", Width = 50, Height = 50, Left = 70, Name = "button2" };
19 button2.BackColor = System.Drawing.Color.Green;
20
21 // C# 2中使用匿名方法来订阅事件
22 button1.Click += delegate (object sender, EventArgs e)
23 {
24 ReportEvent("Click事件", sender, e);
25 };
26
27
28 // C# 3Lambda表达式方式来订阅事件
29 button2.Click += (sender, e) => ReportEvent("Click事件", sender, e);
30
31
32 Form form = new Form { Name = "在控制台中创建的窗体", AutoSize = true };
33
34 form.Controls.Add(button1);
35 form.Controls.Add(button2);
36 // 运行窗体
37
38 string str = "";
39 bool isShow = false;
40 while (!isShow)
41 {
42 str = Console.ReadLine();
43 switch (str)
44 {
45 case "show":
46 isShow = true;
47 Application.Run(form);
48 break;
49 case "quit":
50 Environment.Exit(0);
51 break;
52
53 }
54 }
55 Console.ReadKey();
56 }
57 // 记录事件的回调方法
58 private static void ReportEvent(string title, object sender, EventArgs e)
59 {
60 Console.WriteLine("事件名称：{0}", title);
61 Console.WriteLine("激发事件的对象：{0}", (sender as Button).Name);
62 Console.WriteLine("事件参数类型： {0}", e.GetType());
63 Console.WriteLine();
64 Console.WriteLine();
65 }
66 }
67 }
运行结果如下：
