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 = -1;

            
            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);

        }