ListView的getChildAt返回null可见儿童 [英] ListView getChildAt returning null for visible children

问题描述

我碰到一个ListView /的getChildAt方法，一些奇怪的行为。

I'm getting some strange behavior from a listview/the getChildAt method.

我有一个HashSet已在数据库中更改图标，iconsToUpdate。我想遍历可见的行，看看是否有自己的图标，需要进行更新，以反映新的图标。我并不需要考虑当前未测试的图标，因为它们呈现时将被正确绘制。

I have a HashSet, iconsToUpdate, of icons that have been changed in the database. I want to iterate over the visible rows to see if any of their icons need to be updated to reflect the new icons. I don't need to test the icons not currently in view as they will be drawn properly when rendered.

我的问题是getChildAt将返回null，则好像不应该。我知道getChildAt只能返回看法是当前可见的，但它返回null对于一些可见行。

My problem is that getChildAt is returning null when it seems like it shouldn't. I know that getChildAt can only return views that are currently visible, but it is returning null for some of the visible rows.

下面是我的code，它遍历可见行：

Here is my code that iterates over the visible rows:

Logger.debug("First visible index: " + f_listView.getFirstVisiblePosition());
Logger.debug("Last visible index: " + f_listView.getLastVisiblePosition());
for (int i = f_listView.getFirstVisiblePosition(); i <= f_listView.getLastVisiblePosition(); i++) {
    String tag = "asdf"; // Remove when bug is fixed.
    if (f_listView == null) {
        Logger.debug("f_listView is null");
    } else if (f_listView.getChildAt(i) == null) {
        Logger.debug("Child at index " + i + " is null");
    } else {
        tag = (String) f_listView.getChildAt(i).getTag();
        Logger.debug("Successful at index " + i + ", tag is: " + tag);
    }
    if (iconsToUpdate.contains(tag)) {
        setIcon(i, f_aim.getInHouseIcon(tag));
    }
}

下面是日志对应于这个循环的运行：

Here is the log corresponding to a run of this loop:

D/...: First visible index: 3
D/...: Last visible index: 8
D/...: Successful at index 3, tag is: ...
D/...: Successful at index 4, tag is: ...
D/...: Successful at index 5, tag is: ...
D/...: Child at index 6 is null
D/...: Child at index 7 is null
D/...: Child at index 8 is null

应该注意的是，第一和最后一个可见指标是否被正确的报道，因为我看行3-8当我运行这一点。行6，7，8正在呈现正常。如何显示他们，如果他们是空？

It should be noted that the first and last visible indexes are being correctly reported, as I am viewing rows 3-8 when I run this. Rows 6, 7, 8 are being rendered properly. How are they being displayed if they are null?

另外，我不知道这是重要的，但第5行是最后一个可见行，当我在列表视图的顶部。

Also, I do not know if this is important, but row 5 is the last visible row when I am at the top of the listview.

任何信息，为什么这些行正在返回空值将大大AP preciated。

Any info as to why these rows are being returned as null would be greatly appreciated.

谢谢！

推荐答案

listView.getChildAt（我）的作品，其中0是第一个可见行和（N-1）是最后一个可见行（其中n是多少你看可见视图）。

listView.getChildAt(i) works where 0 is the very first visible row and (n-1) is the last visible row (where n is the number of visible views you see).

在得到最后一个/第一个可见的回报DataAdapter的你的位置。所以你既然你开始第3位，与什么样子6可见的意见，这时候得到的职位6-8你空。

The get last/first visible return the position in the dataAdapter you have. So you since you start at position 3, with what looks like 6 visible views, that's when get for positions 6-8 you get null.

在你的榜样getChildAt（0）将返回位置3.我通常做的是什么存储在我的意见的立场，所以我可以在我的DataAdapter后，如果我需要值查找。

In your example getChildAt(0) would return position 3. What I usually do is store the position on my views so I can lookup on my dataAdapter later if I need values.

我觉得你的for循环应该是这样的：

I think your for loop should look like this:

for (int i = 0; i <= f_listView.getLastVisiblePosition() - f_listView.getFirstVisiblePosition(); i++) 

希望这有助于。

Hope this helps.

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