获取ListView控件可见的项目 [英] Get ListView Visible items

问题描述

我有一个的ListView 可能包含了很多的项目，所以它是虚拟化和循环利用项目。它不使用排序。我需要更新一些值显示，但是当有太多的项目，实在是太慢了，更新的一切，所以我想只刷新可见项目。

I have a ListView which might contains a lot of items, so it is virtualized and recycling items. It does not use sort. I need to refresh some value display, but when there are too many items, it is too slow to update everything, so I would like to refresh only the visible items.

我怎么能得到当前显示的所有项目的列表？我试图寻找到的ListView 或的ScrollViewer ，但我仍然不知道如何来实现这一目标。该解决方案必须不经过的所有项目，以测试是否可以看到的，因为这将是太慢了。

How could I get a list of all currently displayed items ? I tried to look into the ListView or in the ScrollViewer, but I still have no idea how to achieve this. The solution must NOT go through all items to test if they can be seen, because this would be too slow.

我不知道code或XAML是有用的，它只是一个虚拟化 / 回收的ListView 及其 ItemSource 绑定到一个阵列。

I'm not sure code or xaml would be useful, it is just a Virtualized/Recycling ListView with its ItemSource bound to an Array.

编辑： 答：
感谢akjoshi，我找到了办法：

Edit : Answer :
thanks to akjos I found the way :

• 获得的ScrollViewer 的的ListView （以 FindDescendant 方法，你可以做你自己的 VisualTreeHelper ）。

• get the ScrollViewer of the ListView (with a FindDescendant method, that you can do yourself with the VisualTreeHelper ).

读取其 ScrollViewer.VerticalOffset ：这是显示的第一个项目的数量

read its ScrollViewer.VerticalOffset : it is the number of the first item shown

推荐答案

有一个看MSDN在这个问题上表现出的技术，找出可见的ListView 项目 -

Have a look at this question on MSDN showing a technique to find out the visible ListView items -

如何找到行（ ListViewItem的（S））在ListView，实际上是可见的？

您应该做的另一件事是使用 的ObservableCollection 为你的 ItemSource 而不是一个阵列;这肯定会提高性能。

Another thing you should do is to use ObservableCollection as your ItemSource instead of an Array; that will definitely improve the performance.

更新：

雅那可能是真实的（阵列与的ObservableCollection ），但我想看到一些相关的统计数据本;

Ya that might be true(array vs. ObservableCollection) but I would like to see some statistics related to this;

的ObservableCollection 的真正的好处是，如果你有一个条件，添加/从你的的ListView 在运行删除项目 - 时间，在发生阵列，你将不得不重新分配 ItemSource 中的ListView 和的ListView 第一扔掉了previous项目，并重新生成整个列表。

The real benefit of ObservableCollection is if you have a requirement to add/remove items from your ListView at run-time, in case of an Array you will have to reassign the ItemSource of ListView and the ListView first throws away its previous items and regenerates its entire list.

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