Show only one child of expandable list at a time

Just to confirm bos’s answer in code:

    expandableList.setOnGroupExpandListener(new OnGroupExpandListener() {
        int previousGroup = -1;

        @Override
        public void onGroupExpand(int groupPosition) {
            if(groupPosition != previousGroup)
                expandableList.collapseGroup(previousGroup);
            previousGroup = groupPosition;
        }
    });