How do I determine if System.Type is a custome type or a Framework type?

Question

I want to distinctly determine if the type that I have is of custom class type (MyClass) or one provided by the Framework (System.String).

Is there any way in reflection that I can distinguish my class type from system.string or other Framework provided types?

Answer 1

You can check the Assembly in which the type is declared.

object.GetType().Assembly

Answer 2

If you simply want to distinguish between MyClass and string then you can check for those types directly:

Type typeToTest = GetTypeFromSomewhere();

if (typeToTest == typeof(MyClass))
    MyClassAction();
else if (typeToTest == typeof(string))
    StringAction();
else
    NotMyClassOrString();

If you need a more general check for whether or not a given type is a framework type then you could check whether it belongs to the System namespace:

// create an array of the various public key tokens used by system assemblies
byte[][] systemTokens =
    {
        typeof(System.Object)
            .Assembly.GetName().GetPublicKeyToken(),  // B7 7A 5C 56 19 34 E0 89
        typeof(System.Web.HttpRequest)
            .Assembly.GetName().GetPublicKeyToken(),  // B0 3F 5F 7F 11 D5 0A 3A 
        typeof(System.Workflow.Runtime.WorkflowStatus)
            .Assembly.GetName().GetPublicKeyToken()   // 31 BF 38 56 AD 36 4E 35 
    };

Type typeToTest = GetTypeFromSomewhere();

string ns = typeToTest.Namespace;
byte[] token = typeToTest.Assembly.GetName().GetPublicKeyToken();

bool isSystemType = ((ns == "System") || ns.StartsWith("System."))
                    && systemTokens.Any(t => t.SequenceEqual(token));

Answer 3

Not all framework classes start in the System namespace (they can also be Microsoft etc).

As such, you could probably compare the location of a known framework class with that of the type that you are testing such as:

  if (String.CompareOrdinal(
        Path.GetDirectoryName(typeof(String).Assembly.Location), 
        Path.GetDirectoryName(typeof(MyType).Assembly.Location)
      ) == 0)
  {
    //Framework Type
  }
  else
  {
    //3rd Party DLL
  }

Not the greatest solution; but safer than just testing if the namespace starts with System (I could create a namespace that starts with System that isn't a framework class).

Edit

Also, in addition to the above test, it wouldn't hurt to verify that the type is loaded from the Global Assembly Cache:

typeof(MyType).Assembly.GlobalAssemblyCache