C# 特性（一）

1、数据转换

例如：要把字符串“111”转换为整型，之前方式

int temp;

int.TryParse("111", out temp);

新方式

int.TryParse("111", out int temp);
Console.WriteLine(temp);

 

object a3 = 123;
if (a3 is int a4)
{
var tm1 = 0;
tm1 += a4;
Console.WriteLine(tm1);//
}

以上语句会输出123

2、元组

无参数名称的元组

private static (int, int) Get1()
{
return (1, 3);
}

var a2 = Get1();
Console.WriteLine(a2.Item1); //使用元组时，使用Item1,Item2来对应具体的元组里的元素

具有参数名称的元组

private static (int x, int t) Get()
{
return (1, 3);
}

在使用时直接可以通过参数名称使用

var a1 = Get();
Console.WriteLine(a1.t);

(int x, int y) tmep1 = (1, 2);
var yz = (abc: 1, abc1: 3);
Console.WriteLine(yz.abc);

3、switch语句

通过switch语句进行集合分支判断

IEnumerable<object> enumerableList = new List<object>()
            {
                0,new List<int>(){1,2,3},100,null
            };

            int sum = 0;
            foreach (var at in enumerableList)
            {
                switch (at)
                {
                    case 0:
                        break;
                    case IEnumerable<int> lit:
                        foreach (var t in lit)
                        {
                            sum += t;
                        }
                        break;
                    case int n when n > 0:
                        break;
                    case null:
                        break;
                }
            }

4、枚举和对象属性遍历

       //枚举遍历
        public static string ForEnum(EState state) => state switch
        {
            EState.Close => "ceshi",
            _ => throw new Exception("错误"),
        };

        //相当于如下语句
        public static string ForEnum1(EState state)
        {
            switch (state)
            {
                case EState.Close:
                    return "ceshi";
                default:
                    throw new Exception("错误");
            }
        }

   //属性遍历(属性模式)
        public static string ForProperty(User user) => user switch
        {
            { Name: "ceshi" } => "说明",  //属性Name值为ceshi 返回"说明"
            { Age: 11 } => throw new Exception("错误"),
            _ => throw new Exception("错误")
        };

5、数字文本改进

int sixteen = 0b0001_0000;
long billionsAndBillions = 100_000_000_000;

6、泛型约束

//    unmanaged //非空约束
public class User<T> where T : unmanaged //非空约束
    {
        public void Show(T t)
        {

        }
    }
        User<int> user1 = new User<int>();
            //User<string> user2 = new User<string>();//错误，因为string可为空

7、默认接口方法

    public interface IPersion
    {
        void Show();

        void ShowData()
        {
            Console.WriteLine("afasdfa");
        }
    }

    public class CPersion : IPersion
    {
        public void Show()
        {
            Console.WriteLine("aaaa1111");
        }
    }

 IPersion cPersion = new CPersion();
            cPersion.Show();
            cPersion.ShowData();

8、异常过滤

        public void TesetThrow()
        {
            try
            {
                //throw new Exception("abc");
                throw new Exception("ttt");
            }
            catch (Exception ex) when (ex.Message.Contains("abc"))
            {
                Console.WriteLine(ex);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }