c# - Create an object knowing only the class name?

Question

I have a set of classes, each one is a different strategy to do the same work.

namespace BigCorp.SuperApp
{
    public class BaseClass { }
    public class ClassA : BaseClass { }
    public class ClassB : BaseClass { }
}

The choice of which strategy to use is configurable. I want to configure only the class name 'ClassB' instead of the full type name 'BigCorp.SuperApp.ClassB' in the app.config file.

<appConfig>
   <SuperAppConfig>
      <Handler name="ClassB" />
   </SuperAppConfig>
</appConfig>

However, the reflection calls fail because they expect the full type name, particularly

Type t = Type.GetType("ClassB"); // results in t == null
BaseClass c = Activator.CreateInstance(t) as BaseClass; // fails

How can I get this to work while configuring only the class name? Concatenate the namespace to the class name for full type name? Is there another reflection call that works?

If you think this is useless and I should expect the configuration to contain the full type name, I am open to that solution! Just provide rationale to convince me.

(I will not be loading a type from outside this assembly/namespace)

Answer 1

Either use the assembly-qualified-name, or get hold of the Assembly and use Assembly.GetType(name). In this case, since you want the types in the config file, assembly-qualified is a valid way to go - but since you know all your types are in the same assembly:

Assembly assembly = typeof(SomeKnownType).Assembly; // in the same assembly!
Type type = assembly.GetType(name); // full name - i.e. with namespace (perhaps concatenate)
object obj = Activator.CreateInstance(type);

The static Type.GetType(string) has probing rules that often cause confusion... it looks at the calling assembly, and a few system assemblies - but not all loaded assemblies.