Implementing Interface Members Virtually - CSharp Custom Type

CSharp examples for Custom Type:interface

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Introduction

An implicitly implemented interface member is, by default, sealed.

It must be marked virtual or abstract in the base class in order to be overridden.

An explicitly implemented interface member cannot be marked virtual, nor can it be overridden in the usual manner. It can be reimplemented.

For example: 

public interface IUndoable { void Undo(); }

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

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

Calling the interface member through either the base class or the interface calls the subclass's implementation: 

RichTextBox r = new RichTextBox();
r.Undo();                          // RichTextBox.Undo
((IUndoable)r).Undo();             // RichTextBox.Undo
((TextBox)r).Undo();               // RichTextBox.Undo

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