Question

I have a list of items loaded from a web service JSON. Each of these items has it’s own list of sub-items. Each item has numerous text views. The number of subitems varies dynamically, and consists of multiple textviews. There are at times dozens of items with potentially hundreds of subitems. I want all the information visible all the time, i.e. I do not actually need the “expandable” part of the expandable listview but it seemed the easiest way to get the children and group layout.

Item1
  sub item 1
  sub item 2

Item 2
  sub item 1
  sub item 2
  sub item 3

etc

I have currently implemented an expandable listview and forced the groups to always be expanded. This works, however it is very slow to scroll, not only on the emulator but on my galaxy s2.
I am wondering if there is a better way to achieve this?
I considered a single list view and concatenating the strings in the subitems into a single text view but think that this will not be aesthetically pleasing and I won’t be able to get the layout I want.
I wondered if there is a way to override the listview adapted so that one of the items is an array itself of other items. The adapter could iterate over that array and create new textviews on the fly. I suppose this is what the expandable list view is doing anyway so perhaps this would end up with just as much lag scrolling.

Any help greatly appreciated

Answer 1

You can achieve that with ListView and custom adapter class.

Notice that adapter has methods int getViewTypeCount() and int getItemViewType(int position) which you can overwrite.

look at sample implemation for dataset in Map of lists

public abstract class ExampleMapAdapter<V extends Map<?, ? extends List<?>>> extends BaseAdapter {

    public static final int VIEW_TYPE_HEADER = 0;
    public static final int VIEW_TYPE_LISTITEM = 1;

    protected V data;
    protected int[] sectionsStart;
    protected Object[] sections;
    protected int count;

    public ExampleMapAdapter(V data) {
        this.data = data;
        onSetData();
    }

    @Override
    public int getCount() {
        return count;
    }

    @Override
    public Object getItem(int position) {
        int sectionIndex = getSectionForPosition(position);
        int innerIndex = position - sectionsStart[sectionIndex];
        if(innerIndex == 0) { //head
            return sections[sectionIndex];
        }
        else { //values
            return data.get(sections[sectionIndex]).get(innerIndex - 1);
        }
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public int getViewTypeCount() {
        return 2;
    }

    @Override
    public int getItemViewType(int position) {
        return Arrays.binarySearch(sectionsStart, position) < 0 ? VIEW_TYPE_LISTITEM : VIEW_TYPE_HEADER;
    }

    public int getPositionForSection(int section) {
        return sectionsStart[section];
    }

    public int getSectionForPosition(int position) {
        int section = Arrays.binarySearch(sectionsStart, position);
        return section < 0 ? -section - 2 : section;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        if(getItemViewType(position) == VIEW_TYPE_HEADER) {
            return getHeaderView(position, convertView, parent);
        }
        else {
            return getListItemView(position, convertView, parent);
        }
    }

    @Override
    public void notifyDataSetInvalidated() {
        data = null;
        onSetData();
        super.notifyDataSetInvalidated();
    }

    @Override
    public void notifyDataSetChanged() {
        onSetData();
        super.notifyDataSetChanged();
    }

    protected void onSetData() {
        if(data == null) {
            sectionsStart = null;
            sections = null;
            count = 0;
        }
        else {
            sectionsStart = new int[data.size()];
            sections = data.keySet().toArray(new Object[data.size()]);
            count = 0;
            int i = 0;
            for(List<?> v : data.values()) {
                sectionsStart[i] = count;
                i++;
                count += 1 + v.size();
            }
        }
    }

    protected abstract View getHeaderView(int position, View convertView, ViewGroup parent);

    protected abstract View getListItemView(int position, View convertView, ViewGroup parent);
}

and usage example:

public class ExampleActivity extends Activity {

    class SubItem {
        public final String text;
        public final int number;
        public final boolean checked;
        public SubItem(String text, int number, boolean checked) {
            this.text = text;
            this.number = number;
            this.checked = checked;
        }
    }

    //use LinkedHashMap or TreeMap as other map implementations may not keep key's order
    final Map<String, List<SubItem>> map = new LinkedHashMap<String, List<SubItem>>();
    {
        List<SubItem> list = new ArrayList<SubItem>();
        list.add(new SubItem("sub item", 1, false));
        list.add(new SubItem("sub item", 2, true));
        map.put("Item1", list);
        list = new ArrayList<SubItem>();
        list.add(new SubItem("sub item", 1, true));
        list.add(new SubItem("sub item", 2, false));
        list.add(new SubItem("sub item", 3, false));
        map.put("Item2", list);
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        ListView vList = new ListView(this);
        vList.setAdapter(new ExampleMapAdapter<Map<String, List<SubItem>>>(map) {

            @Override
            protected View getHeaderView(int position, View convertView,
                    ViewGroup parent) {
                TextView v = convertView == null ? 
                        new TextView(parent.getContext()) : (TextView) convertView;
                v.setText((String) getItem(position));
                return v;
            }

            @Override
            protected View getListItemView(int position, View convertView,
                    ViewGroup parent) {
                CheckBox v = convertView == null ? 
                        new CheckBox(parent.getContext()) : (CheckBox) convertView;
                SubItem item = (SubItem) getItem(position);
                v.setText(item.text + " " + item.number);
                v.setChecked(item.checked);
                return v;
            }
        });
        setContentView(vList);
    }
}