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.NET知识梳理——2.反射

 2 years ago
source link: https://www.cnblogs.com/Olive116/p/12340323.html
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1.1        DLL-IL-Metadata-反射

DLL：程序集，包含IL 和Metadada

IL：面向对象中间语言（不太好阅读）

Metadata描述了dll、exe中的各种类、属性、方法、参数等信息。

反射 Reflection： .NET Framework提供的帮助类库，可以读取Metadata。

C# 高级语言经过编译器编译生成DLL/EXE，DLL/EXE中包含了Metadata和IL，CLR先读取DLL/EXE中的Metadata，然后JIT进行二次编译，编译成机器码。

1.2        反射加载DLL，读取类、方法、特性

1.2.1  加载DLL

   Assembly assembly = Assembly.Load("XF.DB.SqlServer");//动态加载，需要提供完整的DLL名，不需要后缀,从exe所在的路径进行查找

   Assembly assembly2 = Assembly.LoadFile(@"C:\HXF_CODE\02.Code\05.NET Code\XF.High.NET.Study\XF.DB.SqlServer\bin\Debug\XF.DB.Sqlserver.dll");

   Assembly assembly3 = Assembly.LoadFrom("XF.DB.SqlServer.dll");

Assembly assembly4 = Assembly.LoadFrom(@"C:\HXF_CODE\02.Code\05.NET Code\XF.High.NET.Study\XF.DB.SqlServer\bin\Debug\XF.DB.Sqlserver.dll");

1.2.2  读取类并创建对象

  Type type = assembly.GetType("XF.DB.SqlServer.SqlServerHelper");//获取类型，需要提供完整的类型名称

                object sqlServerHelper = Activator.CreateInstance(type);

                IDBHelper dbHelper = sqlServerHelper as IDBHelper;

                dbHelper.Query();

  2.2.创建多构造函数对象：

object ctor1 = Activator.CreateInstance(type);

                object ctor2 = Activator.CreateInstance(type, new object[] { 123 });

                object ctor3 = Activator.CreateInstance(type, new object[] { "Olive" });

1.3        反射创建对象，反射+简单工厂+配置文件 

程序可配置，通过配置文件自动切换

实现类必须是事先已有的，且存在运行目录下

没有写死类型，通过配置文件执行，反射创建

可扩展：不修改原有代码，只是增加新的实现，修改配置即可支持新功能

反射动态加载、创建对象，与配置文件结合。

private static string typeStr = ConfigurationManager.AppSettings["IDBHelperConfig"];

//反射动态加载、创建对象结合配置文件

                string[] typeArr = typeStr.Split(',');

                Assembly assembly1 = Assembly.Load(typeArr[1]);

                Type type = assembly1.GetType(typeArr[0]);

                foreach (var ctor in type.GetConstructors())

                    Console.WriteLine(ctor.Name);

                    foreach (var parameter in ctor.GetParameters())

                        Console.WriteLine(parameter.ParameterType);

                object ctor1 = Activator.CreateInstance(type);

                object ctor2 = Activator.CreateInstance(type, new object[] { 123 });

                object ctor3 = Activator.CreateInstance(type, new object[] { "Olive" });

1.4        选修：破坏单例 创建泛型

1.4.1 反射破坏单例

反射破坏单例（调用私有的构造函数）

//反射破坏单例（调用私有的构造函数）

                Assembly assembly5 = Assembly.Load("XF.DB.SqlServer");

                Type type1 = assembly.GetType("XF.DB.SqlServer.Singleton");

                Singleton singleton4 = (Singleton)Activator.CreateInstance(type1, true);

                Singleton singleton5 = (Singleton)Activator.CreateInstance(type1, true);

                Singleton singleton6 = (Singleton)Activator.CreateInstance(type1, true);

                Console.WriteLine($"{object.ReferenceEquals(singleton4, singleton6)}");

1.4.2 反射创建泛型

   Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly.GetType("XF.DB.SqlServer.GenericClass`3");//`3为类型占位符，有几个类型就是几，这里有3个类型

                Type typeMake = type2.MakeGenericType(new Type[] { typeof(string), typeof(int), typeof(DateTime) });//确定泛型的类型

                object genericInstance = Activator.CreateInstance(typeMake);//在创建实例的时候，一定要明确具体的类型

                GenericClass<string,int,DateTime> gc = genericInstance as GenericClass<string, int, DateTime>;

                gc.Show("Olive", 116, DateTime.Now);

1.5        反射调用实例方法、静态方法、重载方法

1.5.1  反射调用实例方法

Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly6.GetType("XF.DB.SqlServer.ReflectionTest");

                object test = Activator.CreateInstance(type2);

                MethodInfo method = type2.GetMethod("Show");//调用无参函数

                method.Invoke(test, null);

                MethodInfo method1 = type2.GetMethod("Show1");//调用有参函数

                method1.Invoke(test,new object[] { "Olive" });

1.5.2  反射调用静态方法

Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly6.GetType("XF.DB.SqlServer.ReflectionTest");

                object test = Activator.CreateInstance(type2);

  MethodInfo method6 = type2.GetMethod("Show4");//调用静态函数，实例可要

                method6.Invoke(test, new object[] { "Olive" });

                MethodInfo method7 = type2.GetMethod("Show4");//调用静态函数，实例为空

                method7.Invoke(null, new object[] {  "Olive" });

1.5.3  反射调用重载方法

Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly6.GetType("XF.DB.SqlServer.ReflectionTest");

                object test = Activator.CreateInstance(type2);

MethodInfo method2 = type2.GetMethod("Show2", new Type[] {  });//调用重载函数，无参

                method2.Invoke(test, null);

                MethodInfo method3 = type2.GetMethod("Show2", new Type[] {typeof(int) });//调用重载函数

                method3.Invoke(test, new object[] { 116 });

                MethodInfo method4 = type2.GetMethod("Show2", new Type[] {typeof(string),typeof(int) });//调用重载函数

                method4.Invoke(test, new object[] { "Olive",116 });

                MethodInfo method5 = type2.GetMethod("Show2", new Type[] { typeof(int) ,typeof(string)});//调用重载函数

                method5.Invoke(test, new object[] { 116,"Olive" });

1.6        调用私有方法 调用泛型方法

1.6.1  反射调用私有方法

  Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly6.GetType("XF.DB.SqlServer.ReflectionTest");

                object test = Activator.CreateInstance(type2);

MethodInfo method8 = type2.GetMethod("Show3",BindingFlags.Instance|BindingFlags.NonPublic);//调用私有函数

                method8.Invoke(test, new object[] { "Olive" });

1.6.2  反射调用泛型方法

  Assembly assembly6 = Assembly.Load("XF.DB.SqlServer");

                Type type2 = assembly6.GetType("XF.DB.SqlServer.GenericMethod");

                object test = Activator.CreateInstance(type2);

                MethodInfo method = type2.GetMethod("Show");//调用无参函数

                var methodNew = method.MakeGenericMethod(new Type[] { typeof(string), typeof(int), typeof(DateTime) });

                methodNew.Invoke(test,new object[] { "Olive", 116, DateTime.Now });

1.6.3  反射调用泛型类型+泛型方法

Type type2 = assembly6.GetType("XF.DB.SqlServer.GenericDouble`1");

                Type type3 = type2.MakeGenericType(new Type[] { typeof(int) });

                object test = Activator.CreateInstance(type3);

                MethodInfo method = type3.GetMethod("Show");

                var methodNew = method.MakeGenericMethod(new Type[] { typeof(string),  typeof(DateTime) });

                methodNew.Invoke(test, new object[] { 116, "Olive", DateTime.Now });

1.7        反射字段和属性，分别获取值和设置值

1.7.1  反射字段、获取、设置值

Assembly assembly6 = Assembly.Load("XF.Model");

                Type type = assembly6.GetType("XF.Model.People");

                object people = Activator.CreateInstance(type);

                foreach(var field in type.GetFields())

                    Console.WriteLine($"{type.Name}.{field.Name}={field.GetValue(people)}");

                    if (field.Name.Equals("Description"))

                        field.SetValue(people, "Good boy");

1.7.2  反射属性、获取、设置值

  Assembly assembly6 = Assembly.Load("XF.Model");

                Type type = assembly6.GetType("XF.Model.People");

                object people = Activator.CreateInstance(type);              

                foreach(var prop in type.GetProperties())

                    Console.WriteLine($"{type.Name}.{prop.Name}={prop.GetValue(people)}");

                    if (prop.Name.Equals("Id"))

                        prop.SetValue(people, 116);

1.8        反射的好处和局限

好处：动态

局限：使用麻烦

避开编译器检查

性能问题：正常情况下基本上不存在性能问题


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