Can I use Activator.CreateInstance with an Interface?

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Problem :

I have an example:

        Assembly asm = Assembly.Load("ClassLibrary1");
        Type ob = asm.GetType("ClassLibrary1.UserControl1");
        UserControl uc = (UserControl)Activator.CreateInstance(ob);

There I’m creating an instance of a class, but how can I create an instance of a class which implements some interface? i.e. UserControl1 implements ILoad interface.

U: I can cast object to interface later, but I don’t know which type in the assemblies implements the interface.

Solution :

This is some code i have used a few times. It finds all types in an assembly that implement a certain interface:

Type[] iLoadTypes = (from t in Assembly.Load("ClassLibrary1").GetExportedTypes()
                     where !t.IsInterface && !t.IsAbstract
                     where typeof(ILoad).IsAssignableFrom(t)
                     select t).ToArray();

Then you have all types in ClassLibrary1 that implement ILoad.

You could then instantiate all of them:

ILoad[] instantiatedTypes = 
    iLoadTypes.Select(t => (ILoad)Activator.CreateInstance(t)).ToArray();

The only problem with the accepted answer is that you must have a concrete class on your assembly that implements the interface.

To avoid that I have created my CustomActivator that is able to create a dynamic object at runtime and make it implements the desired interface.

I put it on the github:

The call is simple:


You cannot create instance of an interface, but if

UserControl1 implements ILoad inteface

you can use resulting object as ILoad

ILoad uc = (ILoad)Activator.CreateInstance(ob);

Moreover, you do not need to treat it via interface, if you write

UserControl1 uc = (UserControl1)Activator.CreateInstance(ob);

Members of ILoad would be callable as uc.SomeILoadMethod();

What you want can be achieved using a IoC container like `NInject’.
You can configure a container to return a concrete type when you’ve requested an interface.

Interface is an interface. It’s a template. Why would you want to instantiate an interface? Implement the interface and instantiate that class. You can’t instantiate an interface, it doesn’t really make sense.

If the library was referenced in the project you may use:

    static public IEnumerable<Type> GetTypesFromLibrary<T>(String library)
        var MyAsemblies = AppDomain.CurrentDomain.GetAssemblies()
        var Exported = MyAsemblies
        var Asignable = Exported
                         .Where (t=> !t.IsInterface && !t.IsAbstract
                         && typeof(T).IsAssignableFrom(t))
        return Asignable;

    static public T GetInstanceOf<T>(String library, String FullClassName)
        Type Type = GetTypesFromLibrary<T>(library)
                        .Where(t => t.FullName.Equals(FullClassName))
        if (Type != null)
            T Instance = (T)Activator.CreateInstance(Type);
            return Instance;
        return default(T);

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