ListView getChildAt returning null for visible children

user_850908 0
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I'm getting some strange behavior from a listview/the getChildAt method.

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.

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.

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));
    }
}

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

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?

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.

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

Thanks!

listview null android
9 Answers

I know this is very old post. But I'm answering because people are still looking for a work around on ListView getChildAt() null pointer exception.

This is because the ArrayApdater is REMOVING and RECYCLING the views that are not visible yet on the ListView because of height. So that if you have 10 item views, and ListView can display 4 - 5 at a the time :

The Adapter REMOVE the item views at position 5 to 9, so that any attempt to adapter.getChildAt(5... to 9) will cause null pointer exception

The Adapter also RECYCLE the item view, so that any reference you made on position 3 for example will be lost when you scroll down to 5 to 9, and also any Input that you make on position 3 (EditText, Checkbox, etc.) will be recycled when you scroll down to 5 to 9 and will be reused at another position later (ex position 1, 2 or 3, etc.) with the same value

The only way I found to control this is to forget about getting the View and to have :

Attribute HashMap<Integer, ImageView> iconViews or any type you want for handling the values you want to use for each item on the list. The first type must be unique for item like item->getId() or position. Initialize it with new HashMap<>() in the Constructor; in getViews make iconViews.put(position, iconView); Prevent Adapter from using recycled convertView, remove condition if(convertView == null) so that adapter always inflate a brand new view instance. Because the view instance is new each time, you must set the value from HashMap each time also like if it already contains the key if(iconViews.containsKey(position)){iconView = iconViews.get(position))};. Probably in this case there is not tons of Items, so that smooth scrolling won't be a must.

And finally create public methods to get the Values outside of Adapter passing item->getId() Integer as parameter. Ex : public ImageView getIconViewAt(int position) { return iconViews.get(position); } . It will be easy then to select Item from Adapter

See more from my answer.

user_55655440

Try

if (f_listView.getChildCount() > 0){
           f_listView.getChildAt(i) 
}
user_91335690
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