源视频教程：https://www.bilibili.com/video/BV1tK4y1j7Eu

C#7~9版本新语法-官网：

C#7：https://docs.microsoft.com/zh-cn/dotnet/csharp/whats-new/csharp-7

C#8：https://docs.microsoft.com/zh-cn/dotnet/csharp/whats-new/csharp-8

C#9：https://docs.microsoft.com/zh-cn/dotnet/csharp/whats-new/csharp-9

一、C# 6新语法

1.1-自动属性初始化表达式

    public class Student
    {
        public Student(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName = lastName;
        }

        public int? Id { get; set; }

        public string FirstName { get; }
        public string LastName { get; }

        //对只读属性只能通过构造函数对其初始化值
        //public void SetName(string firstName, string lastName)
        //{
        //    FirstName = firstName;
        //    LastName = lastName;
        //}


        //自动属性初始化表达式
        public ICollection<double> Grades { get; } = new List<double>();

        //public override string ToString() => $"{LastName}, {FirstName}";
        //public override string ToString()
        //{
        //    return $"{FirstName}-{LastName}";
        //}

        public override string ToString()=> $"{FirstName}-{LastName}";
        

        public string FullName => $"{FirstName}-{LastName}";  //goes to


        public string FullName1
        {
            get
            {
                return string.Format("{0}-{1}", this.FirstName, this.LastName);
            }
        }

        public string TestName { get; set; }
    }




//1.只读自动属性
{
    Student student = new Student("Richard", "Richard01");
    string fullName = student.ToString();
    string fullName1 = student.FullName;
}

1.2-using static

using System;
using System.Collections.Generic;
using System.Text;

namespace SharpGrammarInfo.SharpSixInfoTest
{
    public class StaticClass
    {
        public static void Next()
        {
            Console.WriteLine("Next");
        }

        public static void NextTo()
        {
            Console.WriteLine("NextTo");
        }

        public static void ExceptionShow()
        {
            try
            {
                throw new Exception("教育");
            }
            catch (Exception ex) when (ex.Message.Contains("教育"))  //把异常的消息过滤，符合我的条件我就处理
            {

                throw;
            } 
        }         
    }
}

//引入命名空间
using static SharpGrammarInfo.SharpSixInfoTest.StaticClass;


//调用
//2.using static
{
    StaticClass.Next();
    StaticClass.NextTo();
    Next();
    NextTo();
}

1.3-Null 条件运算符

 //3.Null 条件运算符
 {
     Student student = null;
     // student.FirstName; //如果student为null  未将对象引用至对象的实例

     //if (student!=null)
     //{
     //    string fullName = student.FullName;
     //}
    
     string fullName = student?.FullName; //得到的结果一定是要支持null

     int?  id = student?.Id; //? 只能为可空类型服务

     student = new Student("AB", "CD");
     fullName = student?.FullName;
     string testName = student?.TestName ?? "朝夕教育";
     student.TestName = "Zhaoxi教育";
     testName = student?.TestName ?? "朝夕教育";
 }

1.4-字符串内插

//4.字符串内插
{ 
    //string.Format();
    //stringBuilder
    //string+
    string firstName = "朝夕";
    string lastName = "教育";
    //输出{}转义
    var strs = $"{{{firstName}}}-{lastName}-{firstName}-{firstName};{firstName}";
}

1.5-异常刷选器

public static void ExceptionShow()
{
    try
    {
        throw new Exception("朝夕教育");
    }
    //把异常的消息过滤，符合我的条件我就处理
    catch (Exception ex) when (ex.Message.Contains("朝夕教育"))  
    {
        throw;
    } 
}

 //5.异常筛选器
 {
     之前都是自定义不同的Exception 继承Exception父类
     StaticClass.ExceptionShow();
 }

1.6-nameof表达式

//6.nameof 表达式
{

    string clasName=  "StaticClass"; 
    string className1 = nameof(StaticClass);
    Console.WriteLine(className1);
    string className2 = nameof(SharpSixInfo);
    Console.WriteLine(className2);
    string className3 = nameof(Student);
    Console.WriteLine(className3); //输出类名字符串
}

1.7-事件（发布订阅模式）

using System.ComponentModel;

namespace SharpGrammarInfo.SharpSix
{
    public class NotifyPropertyChanged : INotifyPropertyChanged
    { 
        public string LastName
        {
            get { return lastName; }
            set
            {
                if (value != lastName)
                {
                    lastName = value;
                    PropertyChanged?.Invoke(this,
                        new PropertyChangedEventArgs(nameof(LastName)));
                }
            }
        }
        private string lastName;

        public event PropertyChangedEventHandler PropertyChanged;
    }
}

//7.事件(发布订阅模式)
{
    ///什么是事件？
    NotifyPropertyChanged notifyPropertyChanged = new NotifyPropertyChanged(); 
    notifyPropertyChanged.PropertyChanged += (object o, PropertyChangedEventArgs b) =>
    {
        
    }; 
    notifyPropertyChanged.LastName = "朝夕教育";
}

1.8-使用索引器初始化关联集合

//8.使用索引器初始化关联集合
{
    Dictionary<int, string> messages = new Dictionary<int, string>
    {
        { 404, "Page not Found"},
        { 302, "Page moved, but left a forwarding address."},
        { 500, "The web server can't come out to play today."}
    };

    messages.Add(405,"朝夕教育");
    messages.Remove(405, out string obj);

    Console.WriteLine(obj);


    Dictionary<int, string> webErrors = new Dictionary<int, string>
    {
        [404] = "Page not Found",
        [302] = "Page moved, but left a forwarding address.",
        [500] = "The web server can't come out to play today."
    };
    webErrors.Add(405, "朝夕教育"); 
    webErrors.Remove(405, out string  strResult); 
}