C＃：通用接口转换错误

Question

I'm actually trying to make a Base MVP framework for my system. I have IPresenter , IView , PresenterBase<IView> and ViewBase<IPresenter> .

Here is the code:

public interface IPresenter
{
    IAppController GetAppController();
}

public interface IView
{
    void AttachPresenter<T>(T presenter) where T : IPresenter;
}

public abstract class BasePresenter<TView> : IPresenter where TView : class, IView
{
    protected readonly TView View;
    protected readonly IAppController AppController;

    protected BasePresenter(TView view, IAppController appController)
    {
        View = view;
        AppController = appController;
        View.AttachPresenter(this);
    }

    public IAppController GetAppController()
    {
        return AppController;
    }
}

public class BaseView<TPresenter> : Form, IView where TPresenter : class, IPresenter
{
    protected TPresenter Presenter;

    public void AttachPresenter<T>(T presenter) where T : IPresenter
    {
        Presenter = presenter;  // <-- ERROR HERE
    }
}

When I try to set the Presenter with AttachPresenter method, I get this error:

" Cannot implicitly convert type 'T' to 'TPresenter' "

Why? Both are implementing IPresenter . How can I solve it? I want this generic classes to implement every view and presenter in the system.

Sorry for bad english, I hope you understand.

Answer 1

Since you need same type of presenter you can just use:

public void AttachPresenter(TPresenter presenter) 
{
    Presenter = presenter;  
}

Answer 2

although T and TPresenter are implementing IPresenter , but the complier don't think there are same object, for example: you have an IAnimal , and both Cat and Dog implement IAnimal , but you can NOT assign a Cat to Dog like this dog = cat , i think that's the reason.

so, why not just change your function to

public void AttachPresenter(TPresenter presenter)
{
    Presenter = presenter;  
}