C# Loading a type from a string and declaring a List

Question

I have a method that is designed to accept a List in it's declaration as follows:

public class MyHandler
{
    public T LookUp<T>()
    {
        //This method compiles and returns a dynamically typed List
        ...
    }
}

I call this method from elsewhere as such:

MyHandler mh = new MyHandler();
List<AgeGroup> ageGroups = mh.LookUp<List<AgeGroup>>();

This process works great, but I am looking for a way of being able to dynamically load the AgeGroup type from a string.

I have found examples like this, but am not able to work out how to implement it in this case. For example, I have tried the following (and does not compile):

Type t = Assembly.Load("MyNamespace").GetType("MyNamespace.AgeGroup");
List<t> ageGroups = mh.LookUp<List<t>>();

I also tried using typeof(t), but to no avail. Any ideas?

Answer 1

You can construct a generic type at runtime like this:

Type listType = typeof(List<>);
Type typeArg = Assembly.Load("MyNamespace").GetType("MyNamespace.AgeGroup");
listType = listType.MakeGenericType(typeArg);
IList list = (IList)Activator.CreateInstance(listType);

Of course you won't be able to use it as a List<AgeGroup> unless you know the type parameter at compile time. You also won't be able to use Lookup<T> like you did in your example unless you know the type at compile time. You'd have to invoke it like this:

MethodInfo lookupMethod = mh.GetType().GetMethod("LookUp");
lookupMethod = lookupMethod.MakeGenericMethod(listType);
lookupMethod.Invoke(mh, null);