Question

Does anyone know how to iterate over a generic list if the type of that list isn’t known until runtime?

For example, assume obj1 is passed into a function as an Object:

Dim t As Type = obj1.GetType If t.IsGenericType Then     Dim typeParameters() As Type = t.GetGenericArguments()     Dim typeParam As Type = typeParameters(0) End If 

If obj is passed as a List(Of String) then using the above I can determine that a generic list (t) was passed and that it’s of type String (typeParam). I know I am making a big assumption that there is only one generic parameter, but that’s fine for this simple example.

What I’d like to know is, based on the above, how do I do something like this:

For Each item As typeParam In obj1     'do something with it here Next 

Or even something as simple as getting obj1.Count().

Answer 1

If you know that obj is a Generic List. Then you’re in luck.

Generic List implements IList and IEnumerable (both are non-generic). So you could cast to either of those interfaces and then For Each over them.

• IList has a count property.
• IList also has a Cast method. If you don’t know the type to cast to, use object. This will give you an IEnumerable(Of object) that you can then start using Linq against.