C# - How to access internal class from external assembly

Question

Hi,

Having an assembly which I cannot modify (vendor-supplied) which have a method returning an object type but is really of an internal type.

How can I access the fields and/or methods of the object from my assembly?

Keep in mind that I cannot modify the vendor-supplied assembly.

In essence, here's what I have:

From vendor:

internal class InternalClass
  public string test;
end class

public class Vendor
  private InternalClass _internal;
  public object Tag {get{return _internal;}}
end class

From my assembly using the vendor assembly.

public class MyClass
{
  public void AccessTest()
  {
    Vendor vendor = new Vendor();
    object value = vendor.Tag;
    // Here I want to access InternalClass.test
  }
}

Answer 1

Without access to the type (and no "InternalsVisibleTo" etc) you would have to use reflection. But a better question would be: should you be accessing this data? It isn't part of the public type contract... it sounds to me like it is intended to be treated as an opaque object (for their purposes, not yours).

You've described it as a public instance field; to get this via reflection:

object obj = ...
string value = (string)obj.GetType().GetField("test").GetValue(obj);

If it is actually a property (not a field):

string value = (string)obj.GetType().GetProperty("test").GetValue(obj,null);

If it is non-public, you'll need to use the BindingFlags overload of GetField/GetProperty.

Important aside: be careful with reflection like this; the implementation could change in the next version (breaking your code), or it could be obfuscated (breaking your code), or you might not have enough "trust" (breaking your code). Are you spotting the pattern?

Answer 2

Well, you can't. Internal classes can't be visible outside of their assembly, so no explicit way to access it directly -AFAIK of course. The only way is to use runtime late-binding via reflection, then you can invoke methods and properties from the internal class indirectly.

Answer 3

Reflection.

using System.Reflection;

Vendor vendor = new Vendor();
object tag = vendor.Tag;

Type tagt = tag.GetType();
FieldInfo field = tagt.GetField("test");

string value = field.GetValue(tag);

Use the power wisely. Don't forget error checking. :)

Answer 4

I see only one case that you would allow exposure to your internal members to another assembly and that is for testing purposes.

Saying that there is a way to allow "Friend" assemblies access to internals:

In the AssemblyInfo.cs file of the project you add a line for each assembly.

[assembly: InternalsVisibleTo("name of assembly here")]

this info is available here.

Hope this helps.