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;
}