自定义Behavior 实现Listbox自动滚动到选中项

blend为我们提供方便的behavior来扩展我们的控件，写好之后就可以在blend中方便的使用了。

下面是自定义的behavior来实现Listbox自动滚动到选中项

其中this.AssociatedObject为使用该行为的控件。

其中

OnAttached()和OnDetaching()为必须重写的内容，通常可以在OnAttched（）里面添加事件处理程序，来达到拓展的目的。

public class AutoScrollBehavior : Behavior<ListBox>
    {
        protected override void OnAttached()
        {
            base.OnAttached();
            this.AssociatedObject.SelectionChanged += new SelectionChangedEventHandler(AssociatedObject_SelectionChanged);
        }
        void AssociatedObject_SelectionChanged(object sender, SelectionChangedEventArgs e)
        {
            if (sender is ListBox)
            {
                ListBox listbox = (sender as ListBox);
                if (listbox.SelectedItem != null)
                {
                    listbox.Dispatcher.BeginInvoke((Action)delegate
                    {
                        listbox.UpdateLayout();
                        listbox.ScrollIntoView(listbox.SelectedItem);
                    });
                }
            }
        }
        protected override void OnDetaching()
        {
            base.OnDetaching();
            this.AssociatedObject.SelectionChanged -=
                new SelectionChangedEventHandler(AssociatedObject_SelectionChanged);
        }
    }

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