Is it possible to eliminate duplicate type parameters in this example?
I have an MVP implementation for a list of items from a domain model.
My question in general is how (or can I) get rid of duplicate type parameters in a particular view and presenter?
I tend to think that I stumbled upon a limitation and should either live with duplication or redesign the classes. Another option: I am missing something obvious. Anyway, that's why I am asking here.
In particular, if you have:
interface IA<T2, T3> { }
class C<T1, T2, T3> where T1 : IA<T2, T3>
Can I get compiled to deduce parameters like T2 and T3, resulting in something like:
interface IB : IA<int, string>
class D : C<IB> { } // can't do this
This compiles. Duplicate parameters are Note, string
and Attachment, string
.
// Abstract View
public interface IView<TItem, TKey>
{
void Fill(TItem[] items);
event SelectEvent<TKey> SelectionChanged;
event MessageEvent Add;
}
// Event Delegates
public delegate void SelectEvent<TKey>(TKey selectedValue);
public delegate bool MessageEvent();
// Model Entities
public class Note { }
public class Attachment { }
// Abstract Presenter
public abstract class Presenter<TView, TItem, TKey> where TView : IView<TItem, TKey>
{
protected TKey SelectedValue { get; private set; }
protected TView View { get; set; }
public Presenter(TView view)
{
View = (TView)view;
View.SelectionChanged += OnSelectionChangedInternal;
View.Add += OnAdd;
}
void OnSelectionChangedInternal(TKey selectedValue) {
this.SelectedValue = selectedValue;
OnSelectionChanged(selectedValue);
}
protected abstract void OnSelectionChanged(TKey selectedVaule);
protected abstract bool OnAdd();
}
// Concrete Views
public interface INotes : IView<Note, string> { }
public interface IAttachments : IView<Attachment, string> { }
// Concrete Presenters
public class NotesPresenter : Presenter<INotes, Note, string> {
public NotesPresenter(INotes view) : base(view) { }
protected override void OnSelectionChanged(string publisherName) { }
protected override bool OnAdd() { return false; }
}
public class AttachmentsPresenter : Presenter<IAttachments, Attachment, string> {
public AttachmentsPresenter(IAttachments view) : base(view) { }
protected override void OnSelectionChanged(string publisherName) { }
protected override bool OnAdd() { return false; }
}
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Minor change for your host. Print your opinion instead. Since your concrete views are implementing the correct interface, it works. See code below.
// Abstract View
public interface IView<TItem, TKey>
{
void Fill(TItem[] items);
event SelectEvent<TKey> SelectionChanged;
event MessageEvent Add;
}
// Event Delegates
public delegate void SelectEvent<TKey>(TKey selectedValue);
public delegate bool MessageEvent();
// Model Entities
public class Note { }
public class Attachment { }
// Abstract Presenter
public abstract class Presenter<TItem, TKey>
{
protected TKey SelectedValue { get; private set; }
protected IView<TItem, TKey> View { get; set; }
public Presenter(IView<TItem, TKey> view)
{
View = view;
View.SelectionChanged += OnSelectionChangedInternal;
View.Add += OnAdd;
}
void OnSelectionChangedInternal(TKey selectedValue)
{
this.SelectedValue = selectedValue;
OnSelectionChanged(selectedValue);
}
protected abstract void OnSelectionChanged(TKey selectedVaule);
protected abstract bool OnAdd();
}
// Concrete Views
public interface INotes : IView<Note, string> { }
public interface IAttachments : IView<Attachment, string> { }
// Concrete Presenters
public class NotesPresenter : Presenter<Note, string>
{
public NotesPresenter(INotes view) : base(view) { }
protected override void OnSelectionChanged(string publisherName) { }
protected override bool OnAdd() { return false; }
}
public class AttachmentsPresenter : Presenter<Attachment, string>
{
public AttachmentsPresenter(IAttachments view) : base(view) { }
protected override void OnSelectionChanged(string publisherName) { }
protected override bool OnAdd() { return false; }
}
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