C# 基础知识-特性

C基础 - 特性

一.特性

1>特性本质就是一个类，直接或者间接的继承了Attribute

2>特性就是在不破话类封装的前提下，加点额外的信息或者行为

特性添加后，编译会在元素内部产生IL,我们没办法直接使用，在metadata中是有的

二.应用场景之-枚举上加描述

运行结果如下图

 1 using System;
 2 using System.Reflection;
 3
 4 namespace ConsoleApp1
 5 {
 6     public enum RunState
 7     {
 8         [RemarkEnum(Remark = "正在运行")]
 9         Running = 0,
10
11         [RemarkEnum(Remark = "停止")]
12         Stop = 1,
13
14         [RemarkEnum(Remark = "完成")]
15         Finish = 2,
16     }
17     class Program
18     {
19         static void Main(string[] args)
20         {
21             Console.WriteLine(RunState.Running.GetRemark());
22             Console.WriteLine(RunState.Stop.GetRemark());
23             Console.WriteLine(RunState.Finish.GetRemark());
24             Console.ReadKey();
25         }
26     }
27     public class RemarkEnumAttribute : Attribute
28     {
29         public string Remark { get; set; }
30     }
31     /// <summary>
32     /// 扩展方法：静态类，静态方法，this这三个部分造成
33     /// 调用的时候，直接对象.方法名
34     /// </summary>
35     public static class RemarkExtend
36     {
37         public static string GetRemark(this Enum enumValue)
38         {
39             Type type = enumValue.GetType();
40             FieldInfo field = type.GetField(enumValue.ToString());
41             if (field.IsDefined(typeof(RemarkEnumAttribute), true))//访问特性的标准流程
42             {
43                 RemarkEnumAttribute attribute = (RemarkEnumAttribute)field.GetCustomAttribute(typeof(RemarkEnumAttribute), true);
44                 return attribute.Remark;
45             }
46             else
47             {
48                 return enumValue.ToString();
49             }
50         }
51     }
52 }

三.应用场景值之-结构体加描述

运行结果如下图

 1 using System;
 2 using System.Reflection;
 3
 4 namespace ConsoleApp1
 5 {
 6     public struct CommPara
 7     {
 8         [StructExten(Remark = "串口号")]
 9         public string CommPort;
10         [StructExten(Remark = "Id号")]
11         public int Id;
12     }
13     class Program
14     {
15         static void Main(string[] args)
16         {
17             CommPara comm = new CommPara()
18             {
19                 CommPort = "Com1",
20                 Id = 10,
21             };
22             Console.WriteLine(comm.GetRemark());
23             Console.ReadKey();
24         }
25     }
26
27     [AttributeUsage(AttributeTargets.Struct | AttributeTargets.Field)]
28     public class StructExtenAttribute : Attribute
29     {
30         public string Remark { get; set; }
31     }
32     public static class RemarkStructExtend
33     {
34         public static string GetRemark(this object enumValue)
35         {
36             string Name = string.Empty;
37             Type type = enumValue.GetType();
38             FieldInfo[] fields = type.GetFields();
39             foreach (var field in fields)
40             {
41                 if (field.IsDefined(typeof(StructExtenAttribute), true))
42                 {
43                     StructExtenAttribute attribute = (StructExtenAttribute)field.GetCustomAttribute(typeof(StructExtenAttribute), true);
44                     Name += $"{ attribute.Remark},";
45                 }
46                 else
47                 {
48                     Name = enumValue.ToString();
49                 }
50             }
51             return Name;
52         }
53     }
54 }

四.访问类，属性，方法上的特性，另外特性上加一些验证行为

调用实例如下：

首先控制台项目中，添加Student类，Manager类，Validate特性类，这些类见下面，添加好后如下图显示的：

 1 using System;
 2
 3 namespace _002_Attribute
 4 {
 5     class Program
 6     {
 7         static void Main(string[] args)
 8         {
 9             try
10             {
11                 Student student = new Student()
12                 {
13                     Name = "小王",
14                     Id = 100,
15                     QQ = 10002,
16                 };
17                 Manager.Show<Student>(student);
18                 Console.ReadKey();
19             }
20             catch (Exception ex)
21             {
22
23             }
24         }
25     }
26 }

运行结果如下图

Student类

 1 using System;
 2
 3 namespace _002_Attribute
 4 {
 5     [Remark(Description = "学生")]
 6     public class Student
 7     {
 8         [Length(1, 5)]
 9         [Remark(Description = "我是Name")]
10         public string Name { get; set; }
11
12         [Remark(Description = "学生的Id")]
13         public int Id { get; set; }
14
15
16         [Long(10001, 999999)]
17         public int QQ { get; set; }
18
19         [Remark(Description = "我在学习")]
20         public void Study([Remark]string name)
21         {
22             Console.WriteLine($"{name} study now!");
23         }
24     }
25 }

Manager类：只要是程序运行的时候，使用特性

 1 using System;
 2 using System.Reflection;
 3
 4 namespace _002_Attribute
 5 {
 6     public class Manager
 7     {
 8         public static void Show<T>(T student)
 9         {
10             Type type = typeof(T);
11             //访问类的特性
12             if (type.IsDefined(typeof(RemarkAttribute), true))//类访问特性
13             {
14                 RemarkAttribute reamrk = (RemarkAttribute)type.GetCustomAttribute(typeof(RemarkAttribute), true);
15                 Console.WriteLine($"我是类上的特性：{reamrk.Description}");
16                 reamrk.Show();
17             }
18
19             Console.WriteLine("******************************************************************");
20             //访问Id属性的特性
21             PropertyInfo property = type.GetProperty("Id");
22             if (property.IsDefined(typeof(RemarkAttribute), true))
23             {
24                 RemarkAttribute remark = (RemarkAttribute)property.GetCustomAttribute(typeof(RemarkAttribute), true);
25                 Console.WriteLine($"我是属性的特性：{remark.Description}");
26                 remark.Show();
27             }
28             Console.WriteLine("******************************************************************");
29             //访问所有属性的特性
30             PropertyInfo[] propertys = type.GetProperties();
31             foreach (var prop in propertys)
32             {
33                 if (prop.IsDefined(typeof(RemarkAttribute), true))
34                 {
35                     RemarkAttribute remark = (RemarkAttribute)prop.GetCustomAttribute(typeof(RemarkAttribute), true);
36                     Console.WriteLine($"我是属性的特性：{remark.Description}");
37                 }
38             }
39
40             Console.WriteLine("******************************************************************");
41             //访问方法的特性
42             MethodInfo method = type.GetMethod("Study");
43             if (method.IsDefined(typeof(RemarkAttribute), true))
44             {
45                 RemarkAttribute remark = (RemarkAttribute)method.GetCustomAttribute(typeof(RemarkAttribute), true);
46                 Console.WriteLine($"我说方法的特性：{remark.Description}");
47                 remark.Show();
48             }
49
50             Console.WriteLine("******************************************************************");
51             //访问方法参数的特性
52             ParameterInfo parameter = method.GetParameters()[0];
53             if (parameter.IsDefined(typeof(RemarkAttribute), true))
54             {
55                 RemarkAttribute remark = (RemarkAttribute)parameter.GetCustomAttribute(typeof(RemarkAttribute), true);
56                 Console.WriteLine($"我是方法参数上的特性：{remark.Description}");
57                 remark.Show();
58             }
59
60             //特性上加一些验证的行为
61             student.Validate();
62
63         }
64     }
65 }

Validate特性类，自定义的特性

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6
 7 namespace _002_Attribute
 8 {
 9     /// <summary>
10     /// 扩展方法：静态类，静态字段，this这单个特征组成的
11     /// </summary>
12     public static class ValidateExtension
13     {
14         public static bool Validate(this object oObject)
15         {
16             Type type = oObject.GetType();
17             foreach (var prop in type.GetProperties())
18             {
19                 if (prop.IsDefined(typeof(AbstractValidateBase), true))
20                 {
21                     object[] attributeArray = prop.GetCustomAttributes(typeof(AbstractValidateBase), true);//得到所有的特性
22                     foreach (AbstractValidateBase attribute in attributeArray)
23                     {
24                         if (!attribute.Validate(prop.GetValue(oObject)))
25                         {
26                             return false;
27                         }
28                     }
29                 }
30             }
31             return true;
32         }
33     }
34     /// <summary>
35     /// 抽象的基类
36     /// </summary>
37     public abstract class AbstractValidateBase : Attribute
38     {
39         public abstract bool Validate<T>(T tValue);
40     }
41     [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
42     public class LengthAttribute : AbstractValidateBase
43     {
44         private int _Min = 0;
45         private int _Max = 0;
46         public LengthAttribute(int min, int max)
47         {
48             this._Min = min;
49             this._Max = max;
50         }
51         public override bool Validate<T>(T tValue)
52         {
53             int length = tValue.ToString().Length;
54             if (length > this._Min && length < this._Max)
55             {
56                 return true;
57             }
58             return false;
59         }
60     }
61     [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
62     public class LongAttribute : AbstractValidateBase
63     {
64         private long _Min = 0;
65         private long _Max = 0;
66         public LongAttribute(long min, long max)
67         {
68             this._Min = min;
69             this._Max = max;
70         }
71         public override bool Validate<T>(T tValue)
72         {
73             if (tValue != null && !string.IsNullOrWhiteSpace(tValue.ToString()))
74             {
75                 if (long.TryParse(tValue.ToString(), out long result))//新语法，out这里不用提前声明变量了，直接写就行了
76                 {
77                     if (result > this._Min && result < this._Max)
78                     {
79                         return true;
80                     }
81                 }
82             }
83             return true;
84         }
85     }
86     public class RemarkAttribute : Attribute
87     {
88         public RemarkAttribute()
89         {
90
91         }
92         public string Description { get; set; }
93         public void Show()
94         {
95             Console.WriteLine($"This is {nameof(RemarkAttribute)}");
96         }
97     }
98 }