文章介绍

  • 学习笔记，基于朝夕教育VIP班课程

  • 文章写的不好，自己看

    反射：

    1. using System.Reflection;

  • 来自于System.Reflection

  • 是一个帮助类库—可以读取dll/exe中metadata和使用metadata

  • 动态的创建dll/exe —Emit技术

    传统方式

  • 定义接口

    1. public interface IDBHelper
    2. {
    3.  void Query();
    4. }

  • 实现接口 ```csharp public class MySqlHelper : IDBHelper { public MySqlHelper() {

    1.  Console.WriteLine($"{this.GetType().Name}被构造");

    }

  1. public void Query()
  2. {
  3.     Console.WriteLine("{0}.Query", this.GetType().Name);
  4. }

}

  2. -  创建对象
  3. ```csharp
  4. IDBHelper dBHelper = new SqlServerHelper();
  5. //IDBHelper dBHelper = new MySqlHelper();
  6. //dBHelper.Query();

反射方式

  1. 动态读取Dll，三种方式

    1. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");//dll名称
    2. //Assembly assembly1 = Assembly.LoadFile(@"D:\ZXWork\Advanced15\20210706Advanced15Course02Reflection-1\Advanced.Project\MyReflecttion\bin\Debug\net5.0\Business.DB.SqlServer.dll");//dll名称 
    3. //Assembly assembly2 = Assembly.Load("Business.DB.SqlServer");//dll名称

  2. 获取某一个具体的类型：参数需要是类的全名称

    1. Type type = assembly.GetType("Business.DB.SqlServer.SqlServerHelper"); //

  3. 创建对象

  • 方法一

    1. object? oInstance = Activator.CreateInstance(type);
    2. //object? oInstanc1= Activator.CreateInstance("Business.DB.SqlServer.dll", "Business.DB.SqlServer.SqlServerHelper");

    调用

    1. a.oInstance.Query();//报错了：

    因为： oInstance当做是一个object类型，object类型是没有Query方法；C#语言是一种强类型语言；编译时决定你是什么类型,以左边为准；不能调用是因为编译器不允许；实际类型一定是SqlServerHelper；

  • 方法二
    如果使用dynamic 作为类型的声明，在调用的时候，没有限制；

    1. dynamic dInstance = Activator.CreateInstance(type);
    2. dInstance.Query();
    3. dInstance.Get(); //报错了--因为SqlServerHelper没有Get方法

  1. 类型转换

    1. SqlServerHelper helper = (SqlServerHelper)oInstance; //不建议这样转换--如果真实类型不一致--会报报错； 
    2. IDBHelper helper = oInstance as IDBHelper;//如果类型一直，就转换，如果不一致；就返回null

  2. 调用方法

    1. helper.Query();

    初步封装

    1. public static IDBHelper CreateInstance1()
    2. {
    3.  Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll"); 
    4.  Type type = assembly.GetType("Business.DB.SqlServer.SqlServerHelper");
    5.  object? oInstance = Activator.CreateInstance(type);
    6.  IDBHelper helper = oInstance as IDBHelper;
    7.  return helper;
    8. }

  • 调用

    1. IDBHelper helper1 = SimpleFactory.CreateInstance1();
    2. helper1.Query();

    反射 SimpleFactory

  • appsetings.json

  • 始终复制appsetings.json文件

    1. "ReflictionConfig": "Business.DB.Orcale.OrcaleHelper,Business.DB.Orcale.dll",

  • 新建SimpleFactory.cs

  • 读取json字符串

    1. public static class CustomConfigManager
    2. {
    3.  //Core 读取配置文件：appsettings
    4.  //1.Microsoft.Extensions.Configuration；
    5.  //2.Microsoft.Extensions.Configuration.Json 
    6.  public static string GetConfig(string key)
    7.  {
    8.      var builder = new ConfigurationBuilder().AddJsonFile("appsettings.json");  //默认读取  当前运行目录
    9.      IConfigurationRoot configuration = builder.Build();
    10.      string configValue = configuration.GetSection(key).Value;
    11.      return configValue;
    12.  }
    13. }
    1. public class SimpleFactory
    2. {
    3.  //创建SqlServerHelper的时候，没有出现SqlserverHelper；没有依赖SqlServerHelper
    4.  //依赖的是两个字符串Business.DB.SqlServer.dll + Business.DB.SqlServer.SqlServerHelper
    6.  //去掉个对细节的依赖的；依赖于抽象--不再依赖于细节；----依赖倒置原则； 增强代码的稳定性；
    7.  public static IDBHelper CreateInstance()
    8.  {  
    9.      string ReflictionConfig = CustomConfigManager.GetConfig("ReflictionConfig"); 
    10.      //Business.DB.SqlServer.SqlServerHelper,Business.DB.SqlServer.dll 
    11.      string typeName = ReflictionConfig.Split(',')[0];
    12.      string dllName = ReflictionConfig.Split(',')[1];
    14.      //Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll"); 
    15.      //Type type = assembly.GetType("Business.DB.SqlServer.SqlServerHelper");
    17.      Assembly assembly = Assembly.LoadFrom(dllName); 
    18.      Type type = assembly.GetType(typeName);
    19.      object? oInstance = Activator.CreateInstance(type);
    20.      IDBHelper helper = oInstance as IDBHelper; 
    21.      return helper; 
    22.  }
    23. }

    结果

  • 如果经理–MySql–Oracle

  • 如果一个新的功能还不存在，只需要把功能实现、dll Copy到执行目录下，修改配置文件— - 不需要停止程序的运行；

  • 扩展一个新的功能进来；

    反射破坏单例

  • 不知道有么用

    调用带参数的构造函数

    ```csharp public class ReflectionTest {

    region Identity

    1.  /// <summary>
    2.  /// 无参构造函数
    3.  /// </summary>
    4.  public ReflectionTest()

    {

    1.  Console.WriteLine($"这里是{this.GetType()}无参数构造函数");

    }

    ///

    /// 带参数构造函数 /// /// public ReflectionTest(string name) {

    1.  Console.WriteLine($"这里是{this.GetType()} 有参数构造函数");

    }

    public ReflectionTest(int id) {

    1.  Console.WriteLine($"这里是{this.GetType()} 有参数构造函数");

    }

  1. public ReflectionTest(int id, string name)
  2. {
  4.     //typeof(int);
  6.     //Type //id.GetType();
  8.     Console.WriteLine($"这里是{this.GetType()} 有参数构造函数");
  9. }
  11. public ReflectionTest(string name,int id )
  12. {
  14.     //typeof(int);
  16.     //Type //id.GetType();
  18.     Console.WriteLine($"这里是{this.GetType()} 有参数构造函数");
  19. }
  21. #endregion
  23.     #region Method
  24.     /// <summary>
  25.     /// 无参方法
  26.     /// </summary>
  27.     public void Show1()
  28. {
  29.     Console.WriteLine($"这里是{this.GetType()}的Show1" );
  30. }
  31. /// <summary>
  32. /// 有参数方法
  33. /// </summary>
  34. /// <param name="id"></param>
  35. public void Show2(int id)
  36. {
  38.     Console.WriteLine($"这里是{this.GetType()}的Show2");
  39. }
  40. /// <summary>
  41. /// 重载方法之一
  42. /// </summary>
  43. /// <param name="id"></param>
  44. /// <param name="name"></param>
  45. public void Show3(int id, string name)
  46. {
  47.     Console.WriteLine($"这里是{this.GetType()}的Show3");
  48. }
  49. /// <summary>
  50. /// 重载方法之二
  51. /// </summary>
  52. /// <param name="name"></param>
  53. /// <param name="id"></param>
  54. public void Show3(string name, int id)
  55. {
  56.     Console.WriteLine($"这里是{this.GetType()}的Show3_2");
  57. }
  58. /// <summary>
  59. /// 重载方法之三
  60. /// </summary>
  61. /// <param name="id"></param>
  62. public void Show3(int id)
  63. {
  65.     Console.WriteLine($"这里是{this.GetType()}的Show3_3");
  66. }
  67. /// <summary>
  68. /// 重载方法之四
  69. /// </summary>
  70. /// <param name="name"></param>
  71. public void Show3(string name)
  72. {
  74.     Console.WriteLine("这里是{this.GetType()}的Show3_4");
  75. }
  76. /// <summary>
  77. /// 重载方法之五
  78. /// </summary>
  79. public void Show3()
  80. {
  82.     Console.WriteLine($"这里是{this.GetType()}的Show3_1");
  83. }
  84. /// <summary>
  85. /// 私有方法
  86. /// </summary>
  87. /// <param name="name"></param>
  88. private void Show4(string name)  //肯定是可以的
  89. {
  90.     Console.WriteLine($"这里是{this.GetType()}的Show4");
  91. }
  92. /// <summary>
  93. /// 静态方法
  94. /// </summary>
  95. /// <param name="name"></param>
  96. public static void Show5(string name)
  97. {
  98.     Console.WriteLine($"这里是{typeof(ReflectionTest)}的Show5");
  99. }
  100. #endregion
  101. }
  2. -  反射调用构造函数
  3. ```csharp
  4. //Type type = null;
  5. //Activator.CreateInstance();//访问的是无参数构造函数创建对象；
  6. //如何访问带参数的构造函数呢？ 
  7. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
  8. Type type = assembly.GetType("Business.DB.SqlServer.ReflectionTest");
  9. //a. 调用无参数构造函数的
  10. object noParaObject = Activator.CreateInstance(type);
  11. //b. 调用有参数的---需要传递一个object类型的数组作为参数，参数按照从昨往右匹配；严格匹配，按照参数的类型去执行对应的和参数类型匹配的构造函数，如果没有匹配的---报异常
  12. object paraObject = Activator.CreateInstance(type, new object[] { 123 });
  13. object paraObject1 = Activator.CreateInstance(type, new object[] { "纯洁的逗比" });
  14. object paraObject2 = Activator.CreateInstance(type, new object[] { 234, "丸印" });
  15. object paraObject3 = Activator.CreateInstance(type, new object[] { "Richard", 456 });

反射调用方法

  • 反射调用构造函数
  • 执行MethodInfo 的Invoke方法，传递方法所在的类的实例对象+参数

    调用无参数的方法

    1. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
    2. Type type = assembly.GetType("Business.DB.SqlServer.ReflectionTest");
    3. object oInstance = Activator.CreateInstance(type);
    4. MethodInfo show1 = type.GetMethod("Show1");
    5. show1.Invoke(oInstance, new object[] { });
    6. show1.Invoke(oInstance, new object[0]);
    7. show1.Invoke(oInstance, null);

    调用有参数的方法

    ```csharp Assembly assembly = Assembly.LoadFrom(“Business.DB.SqlServer.dll”); Type type = assembly.GetType(“Business.DB.SqlServer.ReflectionTest”);

//一个int object oInstance = Activator.CreateInstance(type); MethodInfo show2 = type.GetMethod(“Show2”); show2.Invoke(oInstance, new object[] { 123 });

//STRING INT MethodInfo show31 = type.GetMethod(“Show3”, new Type[] { typeof(string), typeof(int) }); show31.Invoke(oInstance, new object[] { “细雨浮萍”, 234 });

MethodInfo show32 = type.GetMethod(“Show3”, new Type[] { typeof(int) }); show32.Invoke(oInstance, new object[] { 345 });

MethodInfo show33 = type.GetMethod(“Show3”, new Type[] { typeof(string) }); show33.Invoke(oInstance, new object[] { “幸福靓装” });

MethodInfo show34 = type.GetMethod(“Show3”, new Type[0]); show34.Invoke(oInstance, null);

  1. <a name="nnU1O"></a>
  2. #### 调用私有方法，
  4. -  在获取方法的时候，加上参数BindingFlags.NonPublic | BindingFlags.Instance
  5. ```csharp
  6. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
  7. Type type = assembly.GetType("Business.DB.SqlServer.ReflectionTest");
  8. object oInstance = Activator.CreateInstance(type);
  9. MethodInfo show4 = type.GetMethod("Show4", BindingFlags.NonPublic | BindingFlags.Instance);
  10. show4.Invoke(oInstance, new object[] { "String" });

调用静态方法

  1. //ReflectionTest.Show5();
  2. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
  3. Type type = assembly.GetType("Business.DB.SqlServer.ReflectionTest");
  4. object oInstance = Activator.CreateInstance(type);
  5. MethodInfo show5 = type.GetMethod("Show5");
  6. show5.Invoke(null, new object[] { "String" });
  7. show5.Invoke(oInstance, new object[] { "String" });

调用泛型方法

  1. public class GenericMethod
  2. {
  3.     public void Show<T, W, X>(T t, W w, X x)
  4.     {
  5.         Console.WriteLine($"t.type={t.GetType().Name},w.type={ w.GetType().Name},x.type={x.GetType().Name}");
  6.     }
  7. }
  9. public class GenericClass<T, W, X>
  10. {
  11.     public void Show(T t, W w, X x)
  12.     {
  13.         Console.WriteLine($"t.type={t.GetType().Name},w.type={w.GetType().Name},x.type={x.GetType().Name}");
  14.     }
  15. }
  17. public class GenericDouble<T>
  18. {
  19.     public void Show<W, X>(T t, W w, X x)
  20.     {
  21.         Console.WriteLine($"t.type={t.GetType().Name},w.type={w.GetType().Name},x.type={x.GetType().Name}");
  22.     }
  23. }
  • 获取到方法后，先确定类型，严格按照参数类型传递参数就可以正常调用

  • 泛型是延迟声明，调用的时候，确定类型

    1. Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
    2. Type type = assembly.GetType("Business.DB.SqlServer.GenericMethod");
    3. object oInstance = Activator.CreateInstance(type);
    4. MethodInfo show = type.GetMethod("Show");
    5. //在执行之前选哟确定是什么类型； 
    6. MethodInfo genericshow = show.MakeGenericMethod(new Type[] { typeof(int), typeof(string), typeof(DateTime) });
    7. genericshow.Invoke(oInstance, new object[] { 123, "暖风昔人", DateTime.Now });
    8. genericshow.Invoke(oInstance, new object[] { "暖风昔人", 123, DateTime.Now });
    1. {
    2.  Console.WriteLine(typeof(GenericClass<,,>));
    3.  Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
    4.  Type type = assembly.GetType("Business.DB.SqlServer.GenericClass`3");
    5.  Type generType = type.MakeGenericType(new Type[] { typeof(int), typeof(string), typeof(DateTime) });
    6.  object oInstance = Activator.CreateInstance(generType);
    7.  MethodInfo show = generType.GetMethod("Show");
    8.  show.Invoke(oInstance, new object[] { 123, "赤", DateTime.Now });
    9. }
    10. {
    11.  Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");
    12.  Type type = assembly.GetType("Business.DB.SqlServer.GenericDouble`1");
    13.  Type generType = type.MakeGenericType(new Type[] { typeof(int) });
    14.  object oInstance = Activator.CreateInstance(generType);
    15.  MethodInfo show = generType.GetMethod("Show");
    17.  MethodInfo genericMethod = show.MakeGenericMethod(new Type[] { typeof(string), typeof(DateTime) });
    18.  genericMethod.Invoke(oInstance, new object[] { 123, "鱼儿", DateTime.Now });
    19. }

    MVC框架

    http://localhost:64527/Home/Index 就可以调用到Index方法

    反射的性能问题

  • 测试代码

  • 主要损耗性能的是加载dll 的时候会损耗性能

    1. public static void Show()
    2. {
    3.  Console.WriteLine("*******************Monitor*******************");
    4.  long commonTime = 0;
    5.  long reflectionTime = 0;
    6.  {
    7.      Stopwatch watch = new Stopwatch();
    8.      watch.Start();
    9.      for (int i = 0; i < 1000_000; i++) //1000000000
    10.      {
    11.          IDBHelper iDBHelper = new SqlServerHelper();
    12.          iDBHelper.Query();
    13.      }
    14.      watch.Stop();
    15.      commonTime = watch.ElapsedMilliseconds;
    16.  }
    17.  {
    18.      Stopwatch watch = new Stopwatch();
    19.      watch.Start();
    20.      Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");//1 动态加载
    21.      Type dbHelperType = assembly.GetType("Business.DB.SqlServer.SqlServerHelper");//2 获取类型  
    22.      for (int i = 0; i < 1000_000; i++)
    23.      {
    24.          //Assembly assembly = Assembly.LoadFrom("Business.DB.SqlServer.dll");//1 动态加载
    25.          //Type dbHelperType = assembly.GetType("Business.DB.SqlServer.SqlServerHelper");//2 获取类型  
    26.          object oDBHelper = Activator.CreateInstance(dbHelperType);//3 创建对象
    27.          IDBHelper dbHelper = (IDBHelper)oDBHelper;//4 接口强制转换
    28.          dbHelper.Query();//5 方法调用
    29.      }
    30.      watch.Stop();
    31.      reflectionTime = watch.ElapsedMilliseconds;
    32.  }
    34.  Console.WriteLine($"commonTime={commonTime} reflectionTime={reflectionTime}");
    35. }

    反射如何给属性字段设置值和取值？

    如果说People增加一个字段呢？增加一个属性呢？
    !
    普通方法就必须要修改代码—重新编译发布——不稳定

  • SetValue:设置值

  • GetValue:获取值
  • type.GetProperties();//属性
  • type.GetFields()//字段
  • 带有getset的叫属性， ```csharp Type type = typeof(People); object pObject = Activator.CreateInstance(type); //pObject.Id=234； foreach (var prop in type.GetProperties()) { //Console.WriteLine(prop.Name); //逐个属性赋值 if (prop.Name.Equals(“Id”)) {
    1.  prop.SetValue(pObject, 134);
    } else if (prop.Name.Equals(“Name”)) {
    1.  prop.SetValue(pObject, "陈大宝");
    } else if (prop.Name.Equals(“Age”)) {
    1.  prop.SetValue(pObject, 25);
    } else if (prop.Name.Equals(“Age”)) {
    1.  prop.SetValue(pObject, 25);
    } }

//SetValue:设置值 //GetValue:获取值 // type.GetProperties();//属性 //type.GetFields()//字段 foreach (var prop in type.GetProperties()) { Console.WriteLine($”people.{prop.Name}={prop.GetValue(pObject)}”);

  1. if (prop.Name.Equals("Id"))
  2. {
  3.     prop.GetValue(pObject);
  4. }
  5. else if (prop.Name.Equals("Name"))
  6. {
  7.     prop.GetValue(pObject);
  8. }
  9. else if (prop.Name.Equals("Age"))
  10. {
  11.     prop.GetValue(pObject);
  12. }

} ```

反射+ADO.NET时间数据库访问层—手写ORM框架

  • ORM–对象关系映射

  • 可以通过依赖于某个实体对象–做到对数据库中数据的操作

    准备条件

  • 必须有一个Id字段–继承BaseModel

  • 要求实体对象中的属性结构必须和数据完全一致

    Emit技术

    在运行时去动态的生成Dll、Exe包括dll内部的方法、属性、字段
    ————————————————
    版权声明：本文为CSDN博主「Guistar~~」的原创文章，遵循CC 4.0 BY-SA版权协议，转载请附上原文出处链接及本声明。
    原文链接：https://blog.csdn.net/EAyayaya/article/details/124683084