C#利用Emit反射实现AOP，以及平台化框架封装思路

C#利用Emit反射实现AOP，以及平台化框架封装思路

这是前两天扒的一段动态代理AOP代码，用的Emit反射生成子类来实现代理模式，在这里做个小笔记，然后讨论一下AOP框架的实现思路。

　　首先是主函数：

View Code
using ConsoleApplication1;
using System;
using System.Reflection;
using System.Reflection.Emit;

namespace Aop
{
public static class DynamicProxyBuilder
{
private const string dllName = "DynamicProxy.dll";

public static Object Wrap(Type type)
{
Type newType = null;
try
{
Type m_Type = type;
AppDomain domain = AppDomain.CurrentDomain;
AssemblyBuilder m_Assembly = domain.DefineDynamicAssembly(new AssemblyName("DynamicModule"), AssemblyBuilderAccess.RunAndSave);
ModuleBuilder m_Module = m_Assembly.DefineDynamicModule("Module", dllName);
TypeBuilder m_TypeBuilder = m_Module.DefineType(m_Type.Name + "_proxy_" + m_Type.GetHashCode().ToString(), TypeAttributes.Class | TypeAttributes.Public | TypeAttributes.Sealed, m_Type);
MethodInfo[] methodInfos = m_Type.GetMethods();
TypeBuilder[] m_NestedTypeBuilders = new TypeBuilder[methodInfos.Length];
ConstructorBuilder[] m_NestedTypeConstructors = new ConstructorBuilder[methodInfos.Length];
FieldBuilder m_Interceptor = m_TypeBuilder.DefineField("__Interceptor", typeof(Interceptor), FieldAttributes.Private);
FieldBuilder[] m_MultiCastDelegates = new FieldBuilder[methodInfos.Length];
MethodBuilder[] m_CallBackMethods = new MethodBuilder[methodInfos.Length];
ConstructorBuilder m_ConstructorBuilder = m_TypeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, new Type[] { typeof(Interceptor) });

for (Int32 i = 0; i < m_NestedTypeBuilders.Length; i++)
{
m_NestedTypeBuilders[i] = m_TypeBuilder.DefineNestedType("__" + methodInfos[i].Name + "__delegate", TypeAttributes.NestedPrivate | TypeAttributes.Sealed, typeof(MulticastDelegate));
m_NestedTypeConstructors[i] = m_NestedTypeBuilders[i].DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, new Type[] { typeof(Object), typeof(IntPtr) });
m_NestedTypeConstructors[i].SetImplementationFlags(MethodImplAttributes.Runtime | MethodImplAttributes.Managed);
Type[] argsType = GetParameterTypes(methodInfos[i]);
MethodBuilder mb = m_NestedTypeBuilders[i].DefineMethod("Invoke", MethodAttributes.Public, CallingConventions.Standard, methodInfos[i].ReturnType, argsType);
mb.SetImplementationFlags(MethodImplAttributes.Runtime | MethodImplAttributes.Managed);
}

for (Int32 i = 0; i < methodInfos.Length; i++)
{
m_MultiCastDelegates[i] = m_TypeBuilder.DefineField(methodInfos[i].Name + "_field", m_NestedTypeBuilders[i], FieldAttributes.Private);
}

for (Int32 i = 0; i < methodInfos.Length; i++)
{
Type[] argTypes = GetParameterTypes(methodInfos[i]);
m_CallBackMethods[i] = m_TypeBuilder.DefineMethod("callback_" + methodInfos[i].Name, MethodAttributes.Private, CallingConventions.Standard, methodInfos[i].ReturnType, argTypes);
ILGenerator ilGenerator = m_CallBackMethods[i].GetILGenerator();
ilGenerator.Emit(OpCodes.Ldarg_0);
for (Int32 j = 0; j < argTypes.Length; j++)
{
ilGenerator.Emit(OpCodes.Ldarg, j + 1);
}
ilGenerator.Emit(OpCodes.Call, methodInfos[i]);
ilGenerator.Emit(OpCodes.Ret);
}

for (Int32 i = 0; i < methodInfos.Length; i++)
{
Type[] argTypes = GetParameterTypes(methodInfos[i]);
MethodBuilder mb = m_TypeBuilder.DefineMethod(methodInfos[i].Name, MethodAttributes.Public | MethodAttributes.Virtual, CallingConventions.Standard, methodInfos[i].ReturnType, argTypes);
ILGenerator ilGenerator = mb.GetILGenerator();
ilGenerator.Emit(OpCodes.Ldarg_0);
ilGenerator.Emit(OpCodes.Ldfld, m_Interceptor);
ilGenerator.Emit(OpCodes.Ldstr, methodInfos[i].Name);
ilGenerator.Emit(OpCodes.Ldarg_0);
ilGenerator.Emit(OpCodes.Ldfld, m_MultiCastDelegates[i]);
LocalBuilder local = ilGenerator.DeclareLocal(typeof(Object[]));
ilGenerator.Emit(OpCodes.Ldc_I4, argTypes.Length);
ilGenerator.Emit(OpCodes.Newarr, typeof(Object));
ilGenerator.Emit(OpCodes.Stloc, local);
ilGenerator.Emit(OpCodes.Ldloc, local);
for (Int32 j = 0; j < argTypes.Length; j++)
{
ilGenerator.Emit(OpCodes.Ldc_I4, j);
ilGenerator.Emit(OpCodes.Ldarg, j + 1);
ilGenerator.Emit(OpCodes.Box, argTypes[j]);
ilGenerator.Emit(OpCodes.Stelem_Ref);
ilGenerator.Emit(OpCodes.Ldloc, local);
}
ilGenerator.Emit(OpCodes.Call, typeof(Interceptor).GetMethod("Call", new Type[] { typeof(String), typeof(MulticastDelegate), typeof(Object[]) }));
if (methodInfos[i].ReturnType.Equals(typeof(void)))
{
ilGenerator.Emit(OpCodes.Pop);
}
else
{
ilGenerator.Emit(OpCodes.Unbox_Any, methodInfos[i].ReturnType);
}
ilGenerator.Emit(OpCodes.Ret);
}

ILGenerator ilGenerator2 = m_ConstructorBuilder.GetILGenerator();
ilGenerator2.Emit(OpCodes.Ldarg_0);
ilGenerator2.Emit(OpCodes.Call, m_Type.GetConstructor(new Type[] { }));
ilGenerator2.Emit(OpCodes.Ldarg_0);
ilGenerator2.Emit(OpCodes.Ldarg_1);
ilGenerator2.Emit(OpCodes.Stfld, m_Interceptor);
for (Int32 i = 0; i < m_MultiCastDelegates.Length; i++)
{
ilGenerator2.Emit(OpCodes.Ldarg_0);
ilGenerator2.Emit(OpCodes.Ldarg_0);
ilGenerator2.Emit(OpCodes.Ldftn, m_CallBackMethods[i]);
ilGenerator2.Emit(OpCodes.Newobj, m_NestedTypeConstructors[i]);
ilGenerator2.Emit(OpCodes.Stfld, m_MultiCastDelegates[i]);
}
ilGenerator2.Emit(OpCodes.Ret);

newType = m_TypeBuilder.CreateType();

foreach (TypeBuilder tb in m_NestedTypeBuilders)
{
tb.CreateType();
}

m_Assembly.Save(dllName);
}
catch (Exception err)
{
throw err;
}
return Activator.CreateInstance(newType, new Interceptor());
}

internal static Type[] GetParameterTypes(MethodInfo methodInfo)
{
ParameterInfo[] args = methodInfo.GetParameters();
Type[] argsType = new Type[args.Length];
for (Int32 j = 0; j < args.Length; j++)
{
argsType[j] = args[j].ParameterType;
}
return argsType;
}
}
}

　　这个程序在运行时会在bin下创建一个DynamicProxy.dll，里面是用Emit反射生成的代理子类，复写了父类的方法。

　　上面的代码里有一个Interceptor类，封装AOP框架的一个思路就是把这个类提出一个接口，里面有之前、之后、异常等方法，然后让一个抽象类实现这个接口，提供空实现骨架（模板方法模式），把这个抽象类注入到子类构造器当中来构造子类。

　　如果要结合项目造轮子的话，则允许以这个接口为标准二次开发具体的拦截器，并且可以根据需求封装配置界面，来配置针对系统当中哪一个具体操作命令来进行拦截。

　　DynamicProxyBuilder.Wrap这个方法可以封装为一个人性化的框架接口（作为AOP框架的API）来创建代理子类。

　　有必要将拦截器类放入IoC容器当中以防每次反射。

　　最后，动态代理性能很差，至少第一次生成dll很慢，而且看不懂！

　　真不想用框架、要自己写AOP的话，还是直接让最终执行核心方法的类实现拦截器接口，然后直接在自己的框架里调接口吧，这样还看得懂，别搞什么Emit！

　　最后引用马老师的一句经典语录——搞毛飞机啊！