Overriding property definitions with Reflection.Emit

I'm trying to implement this pattern using Reflection.Emit (TypeBuilder):

public class ClassToBeProxied
{
    public virtual object Property1 { get; set; }
}

public class Proxy : ClassToBeProxied
{
    [AttributeToBeAdded]
    public override object Property1
    {
        get
        {
            //do something else to return the object - i.e get it from the database
            return null; //stub
        }
        set
        {
            //do something else to set the object - i.e, save it to a database
        }
    }        
}

If all I were doing was intercepting the get and set methods, then this works:

PropertyInfo info = typeof(ClassToBeProxied).GetProperty("Property1", BindingFlags.Public | BindingFlags.Instance);
{
    MethodBuilder pGet = typeBuilder.DefineMethod("get_" + info.Name, MethodAttributes.Virtual | MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, info.PropertyType, Type.EmptyTypes);
    ILGenerator pILGet = pGet.GetILGenerator();

    //The proxy object
    pILGet.Emit(OpCodes.Ldarg_0);
    //The database
    pILGet.Emit(OpCodes.Ldfld, database);
    //The proxy object
    pILGet.Emit(OpCodes.Ldarg_0);
    //The ObjectId to look for
    pILGet.Emit(OpCodes.Ldfld, f);
    pILGet.Emit(OpCodes.Callvirt, typeof(MongoDatabase).GetMethod("Find", BindingFlags.Public | BindingFlags.Instance, null, new Type[] { typeof(ObjectId) }, null).MakeGenericMethod(info.PropertyType));
    pILGet.Emit(OpCodes.Ret);

    MethodBuilder pSet = typeBuilder.DefineMethod("set_" + info.Name, MethodAttributes.Virtual | MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig, null, new Type[] { info.PropertyType });
    ILGenerator pILSet = pSet.GetILGenerator();
    pILSet.Emit(OpCodes.Ldarg_0);
    pILSet.Emit(OpCodes.Ldarg_1);
    pILSet.Emit(OpCodes.Ldarg_0);
    pILSet.Emit(OpCodes.Ldfld, database);
    pILSet.Emit(OpCodes.Call, typeof(ProxyBuilder).GetMethod("SetValueHelper", BindingFlags.Public | BindingFlags.Static, null, new Type[] { typeof(object), typeof(MongoDatabase) }, null));
    pILSet.Emit(OpCodes.Stfld, f);
    pILSet.Emit(OpCodes.Ret);

    //Edit:  Added fix
    newProp.SetSetMethod(pSet);
    newProp.SetGetMethod(pGet);
}

But what I need to do is also add an attribute to the Property. I can't figure out how to do this.

If I add a new PropertyDefinition:

PropertyBuilder newProp = typeBuilder.DefineProperty(info.Name, PropertyAttributes.None, info.PropertyType, Type.EmptyTypes);
newProp.SetCustomAttribute(new CustomAttributeBuilder(typeof(AttributeToBeAdded).GetConstructor(Type.EmptyTypes), Type.EmptyTypes, new FieldInfo[0], new object[0]));

and then call GetProperties() on the generated type, two properties with the same name appear. However, if I build the code by hand (as in the example above), and call typeof(Proxy).GetProperties(), only one Property (the derived class property) is visible. This is the behavior I need, but I can't seem to get there with Reflection.Emit

Please let me know if I need to add more info to make the question clearer.

So the answer was add this:

newProp.SetSetMethod(pSet);
newProp.SetGetMethod(pGet);

See the edited question.

The answer kind of contradicts http://www.gutgames.com/post/Overridding-a-Property-With-ReflectionEmit.aspx

but it seems to work.

来源：https://stackoverflow.com/questions/8720275/overriding-property-definitions-with-reflection-emit

标签

reflection.emit