C # interface and inheritance issue

Question

I am browsing C # (C ++ background) and I came to this piece of code:

public interface IUndoable { void Undo(); }
public class TextBox : IUndoable
{
    void IUndoable.Undo() { Console.WriteLine ("TextBox.Undo"); }
}

public class RichTextBox : TextBox, IUndoable
{
    public new void Undo() { Console.WriteLine ("RichTextBox.Undo"); }
}

Since a RichTextBox comes from a TextBox, can anyone explain why a RichTextBox also comes from IUndoable ?. I would have thought that the IUndoable interface would be “inherited” along with any other TextBox members that RichTextBox has access to?

As an aside, I guess from what I have read so far that the concept of open, protected, and private inheritance does not exist in C #.

Is this the right conclusion ?. If so, how will this behavior (i.e., inheritance restriction) be implemented in C #?

[change]

: , , - . , ( ) , , , (phew!).

:

:

public class RichTextBox : TextBox, IUndoable
{
    public new void Undo() { Console.WriteLine ("RichTextBox.Undo"); }
}

:

public class RichTextBox : TextBox
{
    public new void Undo() { Console.WriteLine ("RichTextBox.Undo"); }
}

, ( , ). , TextBox?

Answer 1

# ++ .

. TextBox IUdoable,

void IUndoable.Undo() 

void Undo() 

TextBox. , :

TextBox tb = new TextBox();
tb.Undo(); // error
((IUndoable)tb).Undo(); // ok

, , "", RichTextBox IUndoable , :

RichTextBox rtb = new RichTextBox();
rtb.Undo(); // ok

Answer 2

.

interface IUndoable
{
    void Undo();
}

class TextBox : IUndoable
{
    void IUndoable.Undo()
    {
        Console.WriteLine("TextBox.Undo");
    }
}

class RichTexBox : TextBox
{
    public new void Undo()
    {
        Console.WriteLine("RichTextBox.Undo");
    }
}

class FilthyRichTextBox : TextBox, IUndoable
{
    public new void Undo()
    {
        Console.WriteLine("FilthyRichTextBox.Undo");
    }
}

:

IUndoable text = new TextBox();
IUndoable richText = new RichTexBox();
IUndoable filthyRichText = new FilthyRichTextBox();

Console.WriteLine("From the TextBox:");
text.Undo();

Console.WriteLine("From the RichTextBox:");
richText.Undo();

Console.WriteLine("From the FilthyRichTextBox:");
filthyRichText.Undo();

:

---

:
TextBox.Undo
RichTextBox:
TextBox.Undo
FilthyRichTextBox:
FilthyRichTextBox.Undo

Answer 3

RichTextBox IUndoable. ReSharper, , .

AFAIK , " ".

, , sealed.

Answer 4

RichTextBox Undo ( ), , RichTextBox , , , , Undo TextBox . RichTextBox IUndoable , , - , IUndoable, . :

var obj=new RichTextBox();

    obj.Undo(); // hits the new method  
    ((TextBox)obj).Undo(); //hits the parent (old) method.
    ((IUndoable)obj).Undo(); //hits the new method if RichTextBox implements IUndoable and otherwise hits the old method

, Undo , , , , .

Answer 5

, ,

public class IUndoable
{
}
public class TextBox : IUndoable
{
   public new void Undo() { Console.WriteLine ("RichTextBox.Undo"); }
}

public class RichTextBox : TextBox
{
  public new void Undo() { Console.WriteLine ("RichTextBox.Undo"); }
}

Answer 6

You're right. No need to RichtTextBoximplement IUndoable. You can see that the compiler is also not very happy, since the method Undoin RichTextBoxhides the UndoTextBox method (see Keyword new).

The only reason a subclass needs to implement the interface of this base class is when these classes are ComVisible, and you want to also open this interface to COM.