C# Generics methods and returning a object of a parameterized type created in the method from xml

Question

Hi,

I have a method where I would like to return an object instance of parameterized type T ie. Foo<T>.

The type T is instantiated within the method using GetType(), from a string element in an XML file. Since neither the class or method knows about it before it is created, I cant parameterize either.

Is there a way I can return an object of type Foo<T> from the non-generic method?

EDIT: That is a method signature such as:

 public Foo<T> getFooFromXml(string name) {

where the type is created inside, and the method and class are both non-generic?

Answer 1

Yeah, basically you have to get the open generic type and create a closed generic type.

Type openType = typeof(Foo<>);
Type closedType = openType.MakeGenericType(typeof(string));

return Activator.CreateInstance(closedType); // returns a new Foo<string>

EDIT: Note that I used typeof(Foo<>) above, I intentionally left the angle brackets empty.

Answer 2

In response to your edit:

That method signature isn't valid anyway. You need to know T at compile time in order to return Foo from a method. Consider my suggestion in the comments on my last answer where you would have a separate interface IFoo that Foo implements.

class Foo<T> : IFoo {

   public T DoSomething() {
       ...
   }

   object IFoo.DoSomething() {
      return DoSomething();
   }

}

interface IFoo {
   object DoSomething();
}