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ScrollViewer滚动究竟来触发载入数据的Behavior

2024-10-03 19:17:02   217人阅读

近期项目中遇到载入数据的性能问题， 原因是.net4.0的虚拟化支持不够完毕，有好多bug在4.5才修复。 我们仅仅能利用大家通用的做法来延迟载入数据：
每次载入固定少量的数据。当拖动究竟后。继续载入兴许同样数量的数据。

思路：
监听ScrollViewer的VerticalOffsetProperty，假设值达到同意滚动的高度ScrollableHeight，则发出event通知外部处理载入逻辑。

用法：
1.对于ItemsControl编辑控件模板，在当中的ScrollViewer中增加behavior。
<ScrollViewer x :Name="DG_ScrollViewer" Focusable="false">
                                                                                                                                 <i: Interaction.Behaviors>
                                                                                                                                                 <local: ReachingBottomBehavior ReachingBottomEvent="LazyLoadingBehavior_OnReachingBottomEvent" />
                                                                                                                                 </i: Interaction.Behaviors>

在blend中，比較简单。直接对控件右键。编辑模板/副本。进入ScrollViewer后，把这个behavior拖到ScrollViewer的元素下就可以， 生成的代码就是上面的内容。
xmlns:i ="http://schemas.microsoft.com/expression/2010/interactivity"

2.实现上面ReachingBottomEvent的处理逻辑。比方：
  private void LazyLoadingBehavior_OnReachingBottomEvent ()
        {
            var vm = LayoutRoot. DataContext as MainViewModel;
            if (vm != null)
            {
                int count = dtgRoot. Items .Count ;
                for (int i = count ; i < count + 30; i ++)
                {
                    vm .DataItems . Add(
                                     new DataItem ()
                                     {
                                         Item1 = i . ToString(),
                                         Item2 = i . ToString() + i .ToString ()
                                     });
                }
            }
        }


代码例如以下：

 public class ReachingBottomBehavior : Behavior< ScrollViewer>
    {
        public ReachingBottomBehavior ()
        {
            // Insert code required on object creation below this point.
        }

        protected override void OnAttached()
        {
            base.OnAttached ();

            // Insert code that you would want run when the Behavior is attached to an object.
            var dpd = DependencyPropertyDescriptor. FromProperty(ScrollViewer .VerticalOffsetProperty, AssociatedType);
            dpd.AddValueChanged (
                                AssociatedObject,
                                (sender,
                                 args) =>
                                {
                                    RaiseReachingBottomEvent();
                                });
        }

        protected override void OnDetaching()
        {
            base.OnDetaching ();

            // Insert code that you would want run when the Behavior is removed from an object.
        }

        private void RaiseReachingBottomEvent()
        {
            bool isReachingBottom = AssociatedObject. VerticalOffset >= AssociatedObject .ScrollableHeight;
            if (isReachingBottom )
            {
                if (this .ReachingBottomEvent != null)
                {
                    this.ReachingBottomEvent ();
                }
            }
        }

        public event Action ReachingBottomEvent;
    }

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ScrollViewer滚动究竟来触发载入数据的Behavior


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