AOP从静态代理到动态代理（Emit实现）详解

代理生成类采用Emit的方式生成运行时IL代码。

先把代码放在这里：

public class DynamicProxy
 {
 public static TInterface CreateProxyOfRealize<TInterface, TImp>() where TImp : class, new() where TInterface : class
 {
  return Invoke<TInterface, TImp>();
 }

 public static TProxyClass CreateProxyOfInherit<TProxyClass>() where TProxyClass : class, new()
 {
  return Invoke<TProxyClass, TProxyClass>(true);
 }

 private static TInterface Invoke<TInterface, TImp>(bool inheritMode = false) where TImp : class, new() where TInterface : class
 {
  var impType = typeof(TImp);

  string nameOfAssembly = impType.Name + "ProxyAssembly";
  string nameOfModule = impType.Name + "ProxyModule";
  string nameOfType = impType.Name + "Proxy";

  var assemblyName = new AssemblyName(nameOfAssembly);

  var assembly = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.Run);
  var moduleBuilder = assembly.DefineDynamicModule(nameOfModule);

  //var assembly = AppDomain.CurrentDomain.DefineDynamicAssembly(assemblyName, AssemblyBuilderAccess.RunAndSave);
  //var moduleBuilder = assembly.DefineDynamicModule(nameOfModule, nameOfAssembly + ".dll");

  TypeBuilder typeBuilder;
  if (inheritMode)
  typeBuilder = moduleBuilder.DefineType(nameOfType, TypeAttributes.Public, impType);
  else
  typeBuilder = moduleBuilder.DefineType(nameOfType, TypeAttributes.Public, null, new[] { typeof(TInterface) });

  InjectInterceptor<TImp>(typeBuilder, impType.GetCustomAttribute(typeof(InterceptorBaseAttribute))?.GetType(), inheritMode);

  var t = typeBuilder.CreateType();

  //assembly.Save(nameOfAssembly + ".dll");

  return Activator.CreateInstance(t) as TInterface;
 }

 private static void InjectInterceptor<TImp>(TypeBuilder typeBuilder, Type interceptorAttributeType, bool inheritMode = false)
 {
  var impType = typeof(TImp);
  // ---- define fields ----
  FieldBuilder fieldInterceptor = null;
  if (interceptorAttributeType != null)
  {
  fieldInterceptor = typeBuilder.DefineField("_interceptor", interceptorAttributeType, FieldAttributes.Private);
  }
  // ---- define costructors ----
  if (interceptorAttributeType != null)
  {
  var constructorBuilder = typeBuilder.DefineConstructor(MethodAttributes.Public, CallingConventions.Standard, null);
  var ilOfCtor = constructorBuilder.GetILGenerator();

  ilOfCtor.Emit(OpCodes.Ldarg_0);
  ilOfCtor.Emit(OpCodes.Newobj, interceptorAttributeType.GetConstructor(new Type[0]));
  ilOfCtor.Emit(OpCodes.Stfld, fieldInterceptor);
  ilOfCtor.Emit(OpCodes.Ret);
  }

  // ---- define methods ----

  var methodsOfType = impType.GetMethods(BindingFlags.Public | BindingFlags.Instance);

  string[] ignoreMethodName = new[] { "GetType", "ToString", "GetHashCode", "Equals" };

  foreach (var method in methodsOfType)
  {
  //ignore method
  if (ignoreMethodName.Contains(method.Name))
   return;

  var methodParameterTypes = method.GetParameters().Select(p => p.ParameterType).ToArray();

  MethodAttributes methodAttributes;

  if (inheritMode)
   methodAttributes = MethodAttributes.Public | MethodAttributes.Virtual;
  else
   methodAttributes = MethodAttributes.Public | MethodAttributes.HideBySig | MethodAttributes.NewSlot | MethodAttributes.Virtual | MethodAttributes.Final;

  var methodBuilder = typeBuilder.DefineMethod(method.Name, methodAttributes, CallingConventions.Standard, method.ReturnType, methodParameterTypes);

  var ilMethod = methodBuilder.GetILGenerator();

  // set local field
  var impObj = ilMethod.DeclareLocal(impType);  //instance of imp object
  var methodName = ilMethod.DeclareLocal(typeof(string)); //instance of method name
  var parameters = ilMethod.DeclareLocal(typeof(object[])); //instance of parameters
  var result = ilMethod.DeclareLocal(typeof(object));  //instance of result
  LocalBuilder actionAttributeObj = null;

  //attribute init
  Type actionAttributeType = null;
  if (method.GetCustomAttribute(typeof(ActionBaseAttribute)) != null || impType.GetCustomAttribute(typeof(ActionBaseAttribute)) != null)
  {
   //method can override class attrubute
   if (method.GetCustomAttribute(typeof(ActionBaseAttribute)) != null)
   {
   actionAttributeType = method.GetCustomAttribute(typeof(ActionBaseAttribute)).GetType();
   }
   else if (impType.GetCustomAttribute(typeof(ActionBaseAttribute)) != null)
   {
   actionAttributeType = impType.GetCustomAttribute(typeof(ActionBaseAttribute)).GetType();
   }

   actionAttributeObj = ilMethod.DeclareLocal(actionAttributeType);
   ilMethod.Emit(OpCodes.Newobj, actionAttributeType.GetConstructor(new Type[0]));
   ilMethod.Emit(OpCodes.Stloc, actionAttributeObj);
  }

  //instance imp
  ilMethod.Emit(OpCodes.Newobj, impType.GetConstructor(new Type[0]));
  ilMethod.Emit(OpCodes.Stloc, impObj);

  //if no attribute
  if (fieldInterceptor != null || actionAttributeObj != null)
  {
   ilMethod.Emit(OpCodes.Ldstr, method.Name);
   ilMethod.Emit(OpCodes.Stloc, methodName);

   ilMethod.Emit(OpCodes.Ldc_I4, methodParameterTypes.Length);
   ilMethod.Emit(OpCodes.Newarr, typeof(object));
   ilMethod.Emit(OpCodes.Stloc, parameters);

   // build the method parameters
   for (var j = 0; j < methodParameterTypes.Length; j++)
   {
   ilMethod.Emit(OpCodes.Ldloc, parameters);
   ilMethod.Emit(OpCodes.Ldc_I4, j);
   ilMethod.Emit(OpCodes.Ldarg, j + 1);
   //box
   ilMethod.Emit(OpCodes.Box, methodParameterTypes[j]);
   ilMethod.Emit(OpCodes.Stelem_Ref);
   }
  }

  //dynamic proxy action before
  if (actionAttributeType != null)
  {
   //load arguments
   ilMethod.Emit(OpCodes.Ldloc, actionAttributeObj);
   ilMethod.Emit(OpCodes.Ldloc, methodName);
   ilMethod.Emit(OpCodes.Ldloc, parameters);
   ilMethod.Emit(OpCodes.Call, actionAttributeType.GetMethod("Before"));
  }

  if (interceptorAttributeType != null)
  {
   //load arguments
   ilMethod.Emit(OpCodes.Ldarg_0);//this
   ilMethod.Emit(OpCodes.Ldfld, fieldInterceptor);
   ilMethod.Emit(OpCodes.Ldloc, impObj);
   ilMethod.Emit(OpCodes.Ldloc, methodName);
   ilMethod.Emit(OpCodes.Ldloc, parameters);
   // call Invoke() method of Interceptor
   ilMethod.Emit(OpCodes.Callvirt, interceptorAttributeType.GetMethod("Invoke"));
  }
  else
  {
   //direct call method
   if (method.ReturnType == typeof(void) && actionAttributeType == null)
   {
   ilMethod.Emit(OpCodes.Ldnull);
   }

   ilMethod.Emit(OpCodes.Ldloc, impObj);
   for (var j = 0; j < methodParameterTypes.Length; j++)
   {
   ilMethod.Emit(OpCodes.Ldarg, j + 1);
   }
   ilMethod.Emit(OpCodes.Callvirt, impType.GetMethod(method.Name));
   //box
   if (actionAttributeType != null)
   {
   if (method.ReturnType != typeof(void))
    ilMethod.Emit(OpCodes.Box, method.ReturnType);
   else
    ilMethod.Emit(OpCodes.Ldnull);
   }
  }

  //dynamic proxy action after
  if (actionAttributeType != null)
  {
   ilMethod.Emit(OpCodes.Stloc, result);
   //load arguments
   ilMethod.Emit(OpCodes.Ldloc, actionAttributeObj);
   ilMethod.Emit(OpCodes.Ldloc, methodName);
   ilMethod.Emit(OpCodes.Ldloc, result);
   ilMethod.Emit(OpCodes.Call, actionAttributeType.GetMethod("After"));
  }

  // pop the stack if return void
  if (method.ReturnType == typeof(void))
  {
   ilMethod.Emit(OpCodes.Pop);
  }
  else
  {
   //unbox,if direct invoke,no box
   if (fieldInterceptor != null || actionAttributeObj != null)
   {
   if (method.ReturnType.IsValueType)
    ilMethod.Emit(OpCodes.Unbox_Any, method.ReturnType);
   else
    ilMethod.Emit(OpCodes.Castclass, method.ReturnType);
   }
  }
  // complete
  ilMethod.Emit(OpCodes.Ret);
  }
 }
 }								 
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