What's the best way to instantiate a generic from its name?

Question

Assuming I have only the class name of a generic as a string in the form of "MyCustomGenericCollection(of MyCustomObjectClass)" and don't know the assembly it comes from, what is the easiest way to create an instance of that object?

If it helps, I know that the class implements IMyCustomInterface and is from an assembly loaded into the current AppDomain.

Markus Olsson gave an excellent example here, but I don't see how to apply it to generics.

Answer 1

Once you parse it up, use Type.GetType(string) to get a reference to the types involved, then use Type.MakeGenericType(Type[]) to construct the specific generic type you need. Then, use Type.GetConstructor(Type[]) to get a reference to a constructor for the specific generic type, and finally call ConstructorInfo.Invoke to get an instance of the object.

Type t1 = Type.GetType("MyCustomGenericCollection");
Type t2 = Type.GetType("MyCustomObjectClass");
Type t3 = t1.MakeGenericType(new Type[] { t2 });
ConstructorInfo ci = t3.GetConstructor(Type.EmptyTypes);
object obj = ci.Invoke(null);

Answer 2

If you don't mind translating to VB.NET, something like this should work

foreach (Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
{
 // find the type of the item
 Type itemType = assembly.GetType("MyCustomObjectClass", false);
 // if we didnt find it, go to the next assembly
 if (itemType == null)
 {
  continue;
 }
 // Now create a generic type for the collection
 Type colType = assembly.GetType("MyCusomgGenericCollection").MakeGenericType(itemType);;

 IMyCustomInterface result = (IMyCustomInterface)Activator.CreateInstance(colType);
 break;
}

Answer 3

The MSDN article How to: Examine and Instantiate Generic Types with Reflection describes how you can use Reflection to create an instance of a generic Type. Using that in conjunction with Marksus's sample should hopefully get you started.