[.net 面向对象程序设计进阶] (5) Lamda表达式(一) 创建委托

//零个参数
() => MethodName()
//一个参数
(x) => x+x
X=>x+x
//两个及以上参数
(m,n) => m.Length>n
//显式类型参数
(int x,string y)=>y.Length>x

delegate void TestDelegate(string s);
…
TestDelegate myDel = n => { string s = n + " " + "World"; Console.WriteLine(s); };
myDel("Hello");

 this.myButton.Click += new System.EventHandler(this.myButton_Click);

//事件通常委托写法
private void myButton_Click(object sender, EventArgs e)
{
    MessageBox.Show("您好，我是按钮点击事件！");
}

//事件Lambda语句写法
myButton.Click += (sender, e) => { MessageBox.Show("您好，我是按钮点击事件！这是Lambda语句写法"); };

//异步事件普通写法
private async void asyncButton_Click(object sender, EventArgs e)
{
    await MyMethodAsync();
    MessageBox.Show("您好，我是按钮点击事件！异步的哟！");

}
async Task MyMethodAsync()
{            
    await Task.Delay(1000);
}

//异步事件Lambda写法
asyncButton.Click += async (sender, e) => { await MyMethodAsync();  MessageBox.Show("您好，我是按钮点击事件！异步的哟！这是Lambda语句写法"); };
async Task MyMethodAsync()
{            
    await Task.Delay(1000);
}

//Action 无返回值类型的 泛型委托
//匿名方法声明及调用
Action<int, int> act = delegate (int a, int b) {
    Console.WriteLine(a + "+" + b + "=" + (a + b));
};
act(11, 22);
//表达式声明及调用
Action<int, int> actLambda = (a, b) => { Console.WriteLine(a + "+" + b + "=" + (a + b)); };
actLambda(111, 222);

//Func 带返回值的 泛型委托
//匿名方法声明及调用
Func<int, int, string> acc = delegate (int a, int b) {
    return (a + "+" + b + "=" + (a + b));
};
Console.WriteLine(acc(11, 22));
//表达式声明及调用
Func<int, int, string> ac = (a, b) => { return (a + "+" + b + "=" + (a + b)); };
Console.WriteLine(ac(111, 222));

//查询下列数中的奇数 - Lambda写法
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
int oddNumbers = numbers.Count(n => n % 2 == 1);
Console.WriteLine("奇数有："+oddNumbers.ToString()+ "个,Lambda写法");
//查询下列数中的奇数 -Linq查询写法
var oddNumbersFunc = (from num in numbers
                        where num % 2 == 1
                        select num
                    ).Count();

Console.WriteLine("奇数有：" + oddNumbersFunc.ToString() + "个,Linq查询写法");

//TakeWhile只要满足指定的条件就返回，在检检到number中的6时，就返回，其中8 和9 不满足条件，则返回 5 4 1 3 
int[] numbers = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
var firstNumbersLessThan6 = numbers.TakeWhile(n => n < 6);
Console.WriteLine("满足条件就返回的数有：" + firstNumbersLessThan6.Count().ToString() + "个,Lambda写法");
//第二个参数index表示n的索引位置
string NewNumber = String.Empty;
numbers.TakeWhile((n, index) => n >= index).ToList().ForEach(m=> NewNumber+=m +" ");
Console.WriteLine("满足条件就返回的数有：" + NewNumber + ",Lambda写法");

//Lambda的类型推理
List<MyClass> list = new List<MyClass>() {
    new MyClass(){  at1 = "aaa", at2 = 2, at3 = DateTime.Now},
    new MyClass{ at1 = "bbb", at2 = 5, at3 = DateTime.Parse("2015-06-07") },
    new MyClass{ at1 = "aaa", at2 = 1, at3 = DateTime.Parse("2010-11-12")  }
};            
Console.WriteLine("at1为aaa的元素有：" + list.Where(m => m.at1 == "aaa").Count() + "个,Lambda写法"); 

class MyClass {
    public  string at1 { get; set; }
    public int at2 { get; set; }
    public DateTime at3 { get; set; }
}

class Program
{
    static int num = 2;
    static void Main(string[] args)
    {
        int num2 = 7;

        //Lambda表达式的变量范围
        //相对以下表达式内部，一个类的字段num和一个变量num2,下面测试在表达式内部调用
        int[] numbers2 = { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
        //我们对大于num小于num2的数求和
        int sum = numbers2.Where(m => m > num && m < num2).Sum();
        Console.WriteLine("大于num小于num2的和为：" + sum);
        Console.ReadKey();
    }
}