How to work with an interface dynamically loaded from an assembly and invoke its members

Question

I have got some code to load an assembly and get all types, which implement a certain interface, like this (assume asm is a valid and loaded assembly).

var results = from type in asm.GetTypes()
  where typeof(IServiceJob).IsAssignableFrom(type)
  select type;

Now I'm stuck: I need to create instances of these objects and invoke methods and properties on the object. And I need to store the references to the created objects in an array for later usage.

Answer 1

Oh wow - I only blogged about this a few days ago. Here's my method to return instances of all the types that implement a given interface:

private static IEnumerable<T> InstancesOf<T>() where T : class
{
    var type = typeof(T);
    return from t in type.Assembly.GetExportedTypes()
           where t.IsClass
               && type.IsAssignableFrom(t)
               && t.GetConstructor(new Type[0]) != null
           select (T)Activator.CreateInstance(t);
}

If you refactor this to accept an assembly parameter rather than using the interface's assembly, it becomes flexible enough to suit your need.

Answer 2

You can create an instance of a type with the Activator.CreateInstance method:-

IServiceJob x = Activator.CreateInstance(type);

So your code becomes:-

IServiceJob[] results = (from type in asm.GetTypes()
  where typeof(IServiceJob).IsAssignableFrom(type)
  select (IServiceJob)Activator.CreateInstance(type)).ToArray();

(Note change var to IServiceJob[] to make it clear what is being created).