Android Expandable ListView - how to smooth scroll to a child position inside a group?

Question

I have an expandable listview. one of my groups, Group1, has 15 children. how can I smooth scroll to the 10th child upon clicking and expanding Group1?

Thanks.

Answer 1

Override your adapter's onGroupExpanded method and call one the smoothScrollToPosition methods of your ExpandableListView. Something like:

@Override
public void onGroupExpanded(int groupPosition) {
    super.onGroupExpanded(groupPosition);
    // If it's the first group
    if (groupPosition == 0) {
        int scrollTo = groupPosition + 15;
        mExpList.smoothScrollToPositionFromTop(scrollTo, 0);
    }
}

Now remember that if there are other groups expanded before groupPosition the scrollTo will have to take that into account. So you might want to save all the expanded group positions (and their children counts) into an array and loop them every time onGroupExpanded and onGroupCollapsed is called.

That might look something like this:

@Override
public void onGroupExpanded(int groupPosition) {
    super.onGroupExpanded(groupPosition);
    groupStates.put(groupPosition, 1);
    childrenCount.put(groupPosition, getChildrenCount(groupPosition));
    // Loop the group states
    int scrollTo = 0;
    for (int i=0; i<groupStates.size(); i++) {
        int position = groupStates.keyAt(i);
        // Cancel the loop if reached a further expanded group
        if (position > groupPosition) break;

        // 1 is the group to be skipped + its children count
        scrollTo += 1 + childrenCount.get(position);
    }
    // You can select specific child of the recently expanded group, to scroll to
    int childToScrollTo = 15; // make sure is an existing child
    // -1 because positions begin at index 1
    scrollTo = scrollTo - 1 + childToScrollTo;
    mExpList.smoothScrollToPositionFromTop(scrollTo, 0);
}

@Override
public void onGroupCollapsed(int groupPosition) {
    super.onGroupCollapsed(groupPosition);
    groupStates.remove(groupPosition);
    childrenCount.remove(groupPosition);
}

This is however untested so please do make sure you test it properly.