Overriding properties with Reflection.Emit

[Nigel Sampson]

ey all,
I'm in the process of creating a method of
tracking whenever an objects properties are changed. Since
its not possible to alter

existing types I decided to used a proxy generated using
Reflection.Emit which inherits from the object needed

Person p = (Person)ProxyBuilder.Construct(typeof(Person));

this proxy builder overrides the properties of Person and
adds in the nessecary code to trigger the property changed
event.

This is the code to generate the proxy

public static Type Construct(Type type)
{
AssemblyName name = new AssemblyName();
name.Name = "ObjectServerProxies";

AssemblyBuilder assembly =
AppDomain.CurrentDomain.DefineDynamicAssembly(name ,
AssemblyBuilderAccess.Run);

ModuleBuilder module = assembly.DefineDynamicModule
("Proxies");

TypeBuilder proxy = module.DefineType(type.Name
+ "Proxy", TypeAttributes.Public |
TypeAttributes.AutoClass |

TypeAttributes.AnsiClass | TypeAttributes.BeforeFieldInit,
type);

ConstructorBuilder constructor =
proxy.DefineConstructor(MethodAttributes.Public,
CallingConventions.Standard, new Type[0]);

ILGenerator constructorIL =
constructor.GetILGenerator();
ConstructorInfo baseConstructor =
type.GetConstructor(new Type[0]);
constructorIL.Emit(OpCodes.Ldarg_0);
constructorIL.Emit(OpCodes.Call, baseConstructor);
constructorIL.Emit(OpCodes.Ret);

foreach(PropertyInfo propertyInfo in
type.GetProperties())
{
PropertyBuilder property =
proxy.DefineProperty(propertyInfo.Name,
propertyInfo.Attributes, propertyInfo.PropertyType, null);

MethodAttributes attributes =
MethodAttributes.Public | MethodAttributes.HideBySig |
MethodAttributes.SpecialName |

MethodAttributes.Virtual;

MethodBuilder getMethod =
proxy.DefineMethod("get_" + propertyInfo.Name, attributes,
propertyInfo.PropertyType, null);
ILGenerator getIL =
getMethod.GetILGenerator();
getIL.Emit(OpCodes.Ldarg_0);
getIL.Emit(OpCodes.Call,
propertyInfo.GetGetMethod());
getIL.Emit(OpCodes.Ret);

MethodBuilder setMethod =
proxy.DefineMethod("set_" + propertyInfo.Name, attributes,
typeof(void), new

Type[]{propertyInfo.PropertyType});
ILGenerator setIL =
setMethod.GetILGenerator();
setIL.Emit(OpCodes.Ldarg_0);
setIL.Emit(OpCodes.Ldarg_1);
setIL.Emit(OpCodes.Call,
propertyInfo.GetSetMethod());
setIL.Emit(OpCodes.Ldarg_0);
setIL.Emit(OpCodes.Ldstr,
propertyInfo.Name);
setIL.Emit(OpCodes.Newobj, typeof
(PropertyChangedEventArgs));

MethodInfo onPropertyChanged = typeof
(MappedObject).GetMethod("OnPropertyChanged",
BindingFlags.NonPublic |

BindingFlags.Instance);

setIL.Emit(OpCodes.Call,
onPropertyChanged);
setIL.Emit(OpCodes.Ret);

property.SetGetMethod(getMethod);
property.SetSetMethod(setMethod);

}

return proxy.CreateType();
}

Now the problem I'm having is that the properties are not
being overriden, if I use reflection to iterate though the
proxys properties each

property is showing up twice, one with the declaring type
Person and the other with declaring type PersonProxy,
rather than just the

PersonProxy property being displayed.

Any help appreciated.

Thanks
Nigel Sampson