C# 基础知识-特性

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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：

using System;

namespace _002_Attribute
{
   class Program
   {
       static void Main(string[] args)
       {
           try
           {
               Student student = new Student()
               {
                   Name = "小王",
                   Id = 100,
                   QQ = 10002,
               };
               Manager.Show<Student>(student);
               Console.ReadKey();
           }
           catch (Exception ex)
           {

           }
       }
   }
}

运行结果如下图

Student类

using System;

namespace _002_Attribute
{
   [Remark(Description = "学生")]
   public class Student
   {
       [Length(1, 5)]
       [Remark(Description = "我是Name")]
       public string Name { get; set; }

       [Remark(Description = "学生的Id")]
       public int Id { get; set; }


       [Long(10001, 999999)]
       public int QQ { get; set; }

       [Remark(Description = "我在学习")]
       public void Study([Remark]string name)
       {
           Console.WriteLine($"{name} study now!");
       }
   }
}

Manager类：只要是程序运行的时候，使用特性

using System;
using System.Reflection;

namespace _002_Attribute
{
   public class Manager
   {
       public static void Show<T>(T student)
       {
           Type type = typeof(T);
           //访问类的特性
           if (type.IsDefined(typeof(RemarkAttribute), true))//类访问特性
           {
               RemarkAttribute reamrk = (RemarkAttribute)type.GetCustomAttribute(typeof(RemarkAttribute), true);
               Console.WriteLine($"我是类上的特性：{reamrk.Description}");
               reamrk.Show();
           }

           Console.WriteLine("******************************************************************");
           //访问Id属性的特性
           PropertyInfo property = type.GetProperty("Id");
           if (property.IsDefined(typeof(RemarkAttribute), true))
           {
               RemarkAttribute remark = (RemarkAttribute)property.GetCustomAttribute(typeof(RemarkAttribute), true);
               Console.WriteLine($"我是属性的特性：{remark.Description}");
               remark.Show();
           }
           Console.WriteLine("******************************************************************");
           //访问所有属性的特性
           PropertyInfo[] propertys = type.GetProperties();
           foreach (var prop in propertys)
           {
               if (prop.IsDefined(typeof(RemarkAttribute), true))
               {
                   RemarkAttribute remark = (RemarkAttribute)prop.GetCustomAttribute(typeof(RemarkAttribute), true);
                   Console.WriteLine($"我是属性的特性：{remark.Description}");
               }
           }

           Console.WriteLine("******************************************************************");
           //访问方法的特性
           MethodInfo method = type.GetMethod("Study");
           if (method.IsDefined(typeof(RemarkAttribute), true))
           {
               RemarkAttribute remark = (RemarkAttribute)method.GetCustomAttribute(typeof(RemarkAttribute), true);
               Console.WriteLine($"我说方法的特性：{remark.Description}");
               remark.Show();
           }

           Console.WriteLine("******************************************************************");
           //访问方法参数的特性
           ParameterInfo parameter = method.GetParameters()[0];
           if (parameter.IsDefined(typeof(RemarkAttribute), true))
           {
               RemarkAttribute remark = (RemarkAttribute)parameter.GetCustomAttribute(typeof(RemarkAttribute), true);
               Console.WriteLine($"我是方法参数上的特性：{remark.Description}");
               remark.Show();
           }

           //特性上加一些验证的行为
           student.Validate();

       }
   }
}

Validate特性类，自定义的特性

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _002_Attribute
{
   /// <summary>
   /// 扩展方法：静态类，静态字段，this这单个特征组成的
   /// </summary>
   public static class ValidateExtension
   {
       public static bool Validate(this object oObject)
       {
           Type type = oObject.GetType();
           foreach (var prop in type.GetProperties())
           {
               if (prop.IsDefined(typeof(AbstractValidateBase), true))
               {
                   object[] attributeArray = prop.GetCustomAttributes(typeof(AbstractValidateBase), true);//得到所有的特性
                   foreach (AbstractValidateBase attribute in attributeArray)
                   {
                       if (!attribute.Validate(prop.GetValue(oObject)))
                       {
                           return false;
                       }
                   }
               }
           }
           return true;
       }
   }
   /// <summary>
   /// 抽象的基类
   /// </summary>
   public abstract class AbstractValidateBase : Attribute
   {
       public abstract bool Validate<T>(T tValue);
   }
   [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
   public class LengthAttribute : AbstractValidateBase
   {
       private int _Min = 0;
       private int _Max = 0;
       public LengthAttribute(int min, int max)
       {
           this._Min = min;
           this._Max = max;
       }
       public override bool Validate<T>(T tValue)
       {
           int length = tValue.ToString().Length;
           if (length > this._Min && length < this._Max)
           {
               return true;
           }
           return false;
       }
   }
   [AttributeUsage(AttributeTargets.Property | AttributeTargets.Field)]
   public class LongAttribute : AbstractValidateBase
   {
       private long _Min = 0;
       private long _Max = 0;
       public LongAttribute(long min, long max)
       {
           this._Min = min;
           this._Max = max;
       }
       public override bool Validate<T>(T tValue)
       {
           if (tValue != null && !string.IsNullOrWhiteSpace(tValue.ToString()))
           {
               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
               {
                   if (result > this._Min && result < this._Max)
                   {
                       return true;
                   }
               }
           }
           return true;
       }
   }
   public class RemarkAttribute : Attribute
   {
       public RemarkAttribute()
       {

       }
       public string Description { get; set; }
       public void Show()
       {
           Console.WriteLine($"This is {nameof(RemarkAttribute)}");
       }
   }
}

原文链接：https://www.cnblogs.com/dfcq/p/12968843.html

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