silverlight和wpf中暴露 给子类override

 protected virtual void OnSelectionChanged(SelectionChangedEventArgs args)
        {
        }

  public TestTabControl()
         {
             KeyEventHandler handler = null;
             SelectionChangedEventHandler handler2 = null;
             this._updateIndex = true;
             this.SelectedIndex = -;

             if (handler == null)
             {
                 handler = (sender, e) => this.OnKeyDown(e);
             }
             base.KeyDown += handler;

             //make child can override SelectionChanged event
             if (handler2 == null)
             {
                 handler2 = (sender, e) => this.OnSelectionChanged(e);
             }
             this.SelectionChanged += handler2;

             base.IsEnabledChanged += new DependencyPropertyChangedEventHandler(this.OnIsEnabledChanged);
             base.DefaultStyleKey = typeof(TestTabControl);

         }