ScrollViewer滾動到底來觸發加載數據的Behavior · WPF編程之路

最近項目中遇到加載數據的性能問題，原因是.net4.0的虛擬化支持不夠完成，有好多bug在4.5才修復。我們只能利用大家通用的做法來延遲加載數據：每次加載固定少量的數據，當拖動到底后，繼續加載后續相同數量的數據。思路：監聽ScrollViewer的VerticalOffsetProperty，如果值達到允許滾動的高度ScrollableHeight，則發出event通知外部處理加載邏輯。使用方法： 1.對于ItemsControl編輯控件模板，在其中的ScrollViewer中加入behavior。 <ScrollViewer?x?:Name="DG_ScrollViewer"?Focusable="false"> ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????<i:?Interaction.Behaviors> ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????<local:?ReachingBottomBehavior?ReachingBottomEvent="LazyLoadingBehavior_OnReachingBottomEvent" /> ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????</i:?Interaction.Behaviors> 在blend中，比較簡單，直接對控件右鍵，編輯模板/副本，進入ScrollViewer后，把這個behavior拖到ScrollViewer的元素下即可，生成的代碼就是上面的內容。 xmlns:i?="http://schemas.microsoft.com/expression/2010/interactivity" 2.實現上面ReachingBottomEvent的處理邏輯。比如： ?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?() ??????????????????????????????????? }); ?????????????? } ?????????? } ?????? } 代碼如下： 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; ?? } ![](https://box.kancloud.cn/2016-02-02_56b0015c68327.jpg) [![](image/d41d8cd98f00b204e9800998ecf8427e.png)](#)