Listview Getchildat Returning Null for Visible Children

ListView getChildAt returning null for visible children

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).

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.

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.

I think your for loop should look like this:

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

Hope this helps.

Why ListView.getChildAt() is returning null in android

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).

Try this:

listView.getChildAt(positionOfChildYouWantGet - f_listView.getFirstVisiblePosition());

Difference between using getChildAt and listAdapter.getView is that :

The getChildAt is not a method special to a ListView. It is implemented for each ViewGroup (View that can have children).

When your ListView is created, it has no children. Calling its adapter's getView method doesn't change that fact, it doesn't add any children.

Only when your Activity's content gets measured and laid-out, the ListView will start creating child views by calling its adapter's getView method repeatedly and adding the returned Views to its own list of children. Only after that, ListView.getChildAt(x) could return some non-null value.

The ListAdapter.getView method returns brand new Views (or just returns the recycled View) on behalf of ListView/GridView/etc. Your code should never call ListAdapter.getView itself (unless you do a Unit test).

ListView.getChildAt returns an already created View (created earlier by ListAdapter.getView on behalf of the ListView) Note that your ListAdpater may define many many list items (the value returned by getCount), but the ListView hosting the adapter will never have more children than can be visible at any given time on the screen. I.e. your ListAdapter may deal with 1000 list-items, but your ListView will never have more than 6 child Views (depending on size of screen and listview-item, of course).

listview getChildAt() Return null

This produces null:

 TextView textView = (TextView) listView.getChildAt(0);
Log.i("item", textView.getText().toString());

And this does not:

    TextView textView = (TextView) listView.getAdapter().getView(0, null, listView);
Log.i("item", textView.getText().toString());

This example used android.R.layout.simple_list_item_1 so keep in mind that TextView is root view in simple_list_item_1.

ListView.getChildAt(validPosition) returns null

Your adapter needs to know about this selected position so it can be rendered properly in getView(). Just modify the constructor for your adapter to take the int, and update that int value whenever the onclick is called. In general, you should always have all the information you need to recreate the state of your list items within your adapter.

Sometimes listView.getChildAt(int index) returns NULL (Android)

Because of view recycling, listView.getChildAt() will only return a view for the positions it is displaying, and maybe one more. Maybe if you share more of your code we can help you figure out how to best tackle the problem.

How to get all children (visible and invisible) from a ListView?

As you have already seen you can't get all the child row views from a ListView simply because a ListView holds only the views for the visible rows(plus some recycled rows but you can't reach those). The correct way to do what you want is to store whatever data in the adapter's data and retrieve it from there.

But the ListView doesn't keep the current values from RadioGroup in
running time.

I've seen that you have some problems with this so I've adapted some old code to build a basic example, code that you can find here.

What does getChildAt(0) return for a ListView

mListView.getChildAt(i) returns any (partially or fully) visible child where, i can vary from 0 for the first visible child to mListView.getLastVisiblePosition() - mLisView.getFirstVisiblePosition() for the last visible child.

listview getChildAt return wrong child

You need to simply call getChildAt() with index 0 (or 1 if you list view has some fixed header). This will always be the first visible item, regardless of the position of the data behind it in the backing array.

Related Topics

Leave a reply