使用依赖属性实现监视ListBox滚动到底部

 //自定义依赖属性用来监视ListBox滚动到底事件
    public class ListBoxScrollToBottomNotify
    {
        public static ICommand GetScrollToBottomCommand(DependencyObject obj)
        {
            return (ICommand)obj.GetValue(ScrollToBottomCommandProperty);
        }

        public static void SetScrollToBottomCommand(DependencyObject obj,ICommand value)
        {
            obj.SetValue(ScrollToBottomCommandProperty,value);
        }

        //滚动到底问时响应的事件
       public static readonly DependencyProperty ScrollToBottomCommandProperty =
            DependencyProperty.RegisterAttached("ScrollToBottomCommand",typeof(ICommand),typeof(ListBoxScrollToBottomNotify),new PropertyMetadata(null,OnCommandChanged));

        static void OnCommandChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
        {
            ListBox lb = d as ListBox;
            if (lb != null)
            {
                //确定只绑定一次ListBox的Loaded事件
                if (e.OldValue == null)             
                {
                    lb.Loaded += new RoutedEventHandler(OnListBoxLoaded);
                }
            }
        }
        static void OnListBoxLoaded(object sender,RoutedEventArgs e)
        {
                ListBox lb = sender as ListBox;
                ScrollViewer scrollViewer = FindChildOfType<ScrollViewer>(lb);
                if (scrollViewer != null)
                {
                    VerticalOffsetOfScrollViewNotify monitorVO = new VerticalOffsetOfScrollViewNotify();
                    monitorVO.Attached(scrollViewer);
                    monitorVO.VerticalOffsetChanged = () =>
                    {
                        double verticalOffset = Math.Round(scrollViewer.VerticalOffset);
                        double scrollableHeight = Math.Round(scrollViewer.ScrollableHeight);
                        if (verticalOffset >= scrollableHeight)
                        {
                            ICommand command= GetScrollToBottomCommand(lb);
                            command.Execute(null);
                        }
                    };
                }
        }
        //获取子类型
        static T FindChildOfType<T>(DependencyObject root) where T : class
        {
            var queue = new Queue<DependencyObject>();
            queue.Enqueue(root);

            while (queue.Count > 0)
            {
                DependencyObject current = queue.Dequeue();
                for (int i = VisualTreeHelper.GetChildrenCount(current) - 1; 0 <= i; i--)
                {
                    var child = VisualTreeHelper.GetChild(current,i);
                    var typedChild = child as T;
                    if (typedChild != null)
                    {
                        return typedChild;
                    }
                    queue.Enqueue(child);
                }
            }
            return null;
        }
    }
    //监测ListBox中ScrollView的VerticalOffset改变
    public class VerticalOffsetOfScrollViewNotify
    {
        //通过监控ListBox的MouseMove事件和ManipulationCompleted事件的效果并不好,//当手指在屏幕上划动后ListBox会因为惯性,再滚动一段距离.这样使用前两个事件就不能判断滚动的最后位置
        //现在改成通过依赖属性绑定到ListBox的ScrollView的VerticalOffset来实现
        DependencyProperty VerticalOffsetProperty;

        public VerticalOffsetOfScrollViewNotify()
        {
                 VerticalOffsetProperty = DependencyProperty.RegisterAttached("VerticalOffset",typeof(double),typeof(VerticalOffsetOfScrollViewNotify),new PropertyMetadata(OnVerticalOffsetChanged));
        }
        public  void OnVerticalOffsetChanged(DependencyObject d,DependencyPropertyChangedEventArgs e)
        {
            if (VerticalOffsetChanged != null)
            {
                 VerticalOffsetChanged();
            }
        }

        public Action VerticalOffsetChanged { get; set; }
        public void Attached(FrameworkElement ele)
        {
            if (ele != null)
            {
                ScrollViewer scrollViewer = ele as ScrollViewer;
                Binding binding = new Binding("VerticalOffset") { Source = scrollViewer };
                scrollViewer.SetBinding(VerticalOffsetProperty,binding);
            }
        }
    }

（编辑：李大同）

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