在C＃中使用反射继承

Question

I am in a situation where i have to inherit a class and access its protected method to get a value.

Due to some weird situations i have most of my code in reflection and im hoping if i have any chance to get this working using reflection.

To make things more clear,

Below is the class

public class Converter: BaseConverter
{
    public Converter();
    protected override object StringToValue();
}

I need to do below to get the functionality working.

public class myclass:Converter
{
 public StringToValue()
  {
    base.StringToVaue();
  }
}

However I cannot use direct reference of Converter dll in my project . So i am handicapped here to use inheritance and myclass : converter. So how can i approach this using reflection which would be to basically make myclass inherit the converter class at runtime. I am not sure if it makes sense or not however it seems to me that its where i am trying to head towards to get an answer

Answer 1

You can use TypeBuilder to create a whole new type at runtime via reflection. Of course ultimately you need a reference to the assembly which contains Converter to inherent from it. Make sure to check out the MSDN example of TypeBuidler . You need to call ModuleBuilder.DefineType() which has an overload to specify the parent type.

But if you go that way you have to do everything with reflection including emitting the methods. I don't fully understand your restrictions so that's the best answer I could think of but I don't really like it ;)

While we're talking about hacking: Do you really need to inherit from Converter or do you only need to access its methods? In case you only need the methods you could simply hold an instance of Converter as an attribute of type object and call the protected method via refletion inside your public StringToValue method.

EDIT:

As you ask for sample code. With reflection you can bypass the class security mechanism of C#, which means you're able to call non-public methods on any object. First you need the Type . Because you can't write it out in C# you need to get it some other way. Then you can create an instance of that type with Activator. You also need to obtain information about the method you want to call. It makes sense to cache this information because the processes of reading that information with reflection is kinda slow. Finally you can use the MethodInfo to actually call the method.

I haven't tested that code because I don't have a machine to do so right now.

class myclass
{
    object internalConverter;
    MethodInfo converterStringToValueMethod;

    public myclass()
    {
        // Here you need a reference to the assembly which contains the Converter type
        Assembly asm = Assembly.Load("xxx.dll"); // Name of the assembly which contains Converter
        Type converterType = asm.GetType("Converter");
        this.internalConverter = Activator.CreateInstance(converterType);

        this.converterStringToValueMethod = converterType.GetMethod("StringToValue", BindingFlags.NonPublic | BindingFlags.Instance);
    }

    public object StringToValue()
    {
        return converterStringToValueMethod.Invoke(internalConverter, null);
    }
}

Answer 2

This should do what you want without inheritance:

using System;
using System.Reflection;

namespace Test
{
    class Converter
    {
        string Value;

        public Converter(string test)
        {
            Value = test;
        }
        protected object StringToValue()
        {
            return Value;
        }
    }

    class myclass
    {
        object Unknown;

        public myclass(object other)
        {
            Unknown = other;
        }

        MethodInfo originalFunction;
        public object StringToValue()
        {
            if (originalFunction == null)
            {
                originalFunction = Unknown.GetType().GetMethod("StringToValue", BindingFlags.NonPublic | BindingFlags.Instance);
            }
            return originalFunction.Invoke(Unknown, null);
        }
    }

    class Test
    {
        [System.STAThread]
        public static void Main(string[] args)
        {
            Converter unknown = new Converter("TEST");
            myclass mine = new myclass(unknown);
            Console.WriteLine(mine.StringToValue());
            Console.ReadLine();
        }
    }
}

This is a bad idea for a number of reasons, but if you are sure it is what you need...