android - Is there a way to prevent the listview from scrolling to its top position when its adapter's data is changed?

Question

I'm having a bit of trouble preserving the scroll position of a list view when changing it's adapter's data.

What I'm currently doing is to create a custom ArrayAdapter (with an overridden getView method) in the onCreate of a ListFragment, and then assign it to its list:

mListAdapter = new CustomListAdapter(getActivity());
mListAdapter.setNotifyOnChange(false);
setListAdapter(mListAdapter);

Then, when I receive new data from a loader that fetches everything periodically, I do this in its onLoadFinished callback:

mListAdapter.clear();
mListAdapter.addAll(data.items);
mListAdapter.notifyDataSetChanged();

The problem is, calling clear() resets the listview's scroll position. Removing that call preserves the position, but it obviously leaves the old items in the list.

What is the proper way to do this?

Answer 1

As you pointed out yourself, the call to 'clear()' causes the position to be reset to the top.

Fiddling with scroll-position, etc. is a bit of a hack to get this working.

If your CustomListAdapter subclasses from ArrayAdapter, this could be the issue:

The call to clear(), calls 'notifyDataSetChanged()'. You can prevent this:

mListAdapter.setNotifyOnChange(false); // Prevents 'clear()' from clearing/resetting the listview
mListAdapter.clear();
mListAdapter.addAll(data.items);
// note that a call to notifyDataSetChanged() implicitly sets the setNotifyOnChange back to 'true'!
// That's why the call 'setNotifyOnChange(false) should be called first every time (see call before 'clear()').
mListAdapter.notifyDataSetChanged(); 

I haven't tried this myself, but try it :)