C#: Upper cast - List<Interface> to List<Class> - cast obejct of internal class

Question

I have an interface defined as

public interface INamedReader
{
     string DisplayInfoLine { get; }
     string DisplayName { get; }
}

and a class which implements that interface but it is an internal class

internal class NamedReader : INamedReader, INotifyPropertyChanged
    {
        public NamedReader();

        public string DisplayInfoLine { get; set; }
        public string DisplayName { get; set; }

        public event PropertyChangedEventHandler PropertyChanged;

        public override string ToString();
        protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = "");
        protected virtual bool Set<TField>(ref TField field, TField value, [CallerMemberName] string propertyName = "");
    }

and a class which implements the above NamedReader class

internal class NamedReaderDevice : NamedReader
{
    public NamedReaderDevice();

    public string Id { get; set; }
}

and now i defined class which implements INamedReader

public class ReaderDetails: INamedReader
{
     public string DisplayInfoLine { get; }

     public string DisplayName { get; }
}

I then created a function which return List.

public List<ReaderDetails> GetReaders
{
     var readers = new List<ReaderDetails>();
     var Ireaders = someobject.Getreaders();// Returns the list of NameReaderDevice (which is an internal class).
     // Now i would like cast Ireaders as readers and return.
}

can someone please help me out in this, that would be great.

Answer 1

You are basically trying to convert one class into an entirely different one, like in this picture, trying to convert Class2 to Class3 :

In this scenario, even if they share an interface, you cannot cast between one and the other.

You have a few options:

1. use a method (extension or otherwise) to convert between classes, using Reflection or serialization (not very efficient)
2. use a conversion operator (more details here )
3. return an interface instead of an explicitly implemented class in your Getreaders() method and then use an interface in your application instead of an explicitly implemented class;

In case of (3) if you need or want to further decouple your class implementation, then you may use dependency injection for it (eg. SimpleInjector , accessible through nuget). In that scenario you can for example create objects of said interface in code that does not have acces to the internal class implementing it,