Create easy alphabetical scrolling in ListView?

Question

I\'m looking to emulate the functionality in the latest Music app, namely the nice little cursor that pops up which allows one to scroll super fast to the artist/album/track

Answer 1

Here is the subclass of ArrayAdapter I'm using. Note that the objects I pass in has already been sorted alphabetically, with Collections.sort(objects).

class SectionIndexingArrayAdapter extends ArrayAdapter implements
        SectionIndexer {

    HashMap sectionsMap = new HashMap();
    ArrayList sectionsList = new ArrayList();

    ArrayList sectionForPosition = new ArrayList();
    ArrayList positionForSection = new ArrayList();

    public SectionIndexingArrayAdapter(Context context, int textViewResourceId,
            List objects) {
        super(context, textViewResourceId, objects);

        // Note that List objects has already been sorted alphabetically
        // e.g. with Collections.sort(objects) **before** being passed to
        // this constructor.

        // Figure out what the sections should be (one section per unique
        // initial letter, to accommodate letters that might be missing,
        // or characters like ,)
        for (int i = 0; i < objects.size(); i++) {
            String objectString = objects.get(i).toString();
            if (objectString.length() > 0) {
                String firstLetter = objectString.substring(0, 1).toUpperCase();
                if (!sectionsMap.containsKey(firstLetter)) {
                    sectionsMap.put(firstLetter, sectionsMap.size());
                    sectionsList.add(firstLetter);
                }
            }
        }

        // Calculate the section for each position in the list.
        for (int i = 0; i < objects.size(); i++) {
            String objectString = objects.get(i).toString();
            if (objectString.length() > 0) {
                String firstLetter = objectString.substring(0, 1).toUpperCase();
                if (sectionsMap.containsKey(firstLetter)) {
                    sectionForPosition.add(sectionsMap.get(firstLetter));
                } else
                    sectionForPosition.add(0);
            } else
                sectionForPosition.add(0);
        }

        // Calculate the first position where each section begins.
        for (int i = 0; i < sectionsMap.size(); i++)
            positionForSection.add(0);
        for (int i = 0; i < sectionsMap.size(); i++) {
            for (int j = 0; j < objects.size(); j++) {
                Integer section = sectionForPosition.get(j);
                if (section == i) {
                    positionForSection.set(i, j);
                    break;
                }
            }
        }
    }

    // The interface methods.

    public int getPositionForSection(int section) {
        return positionForSection.get(section);
    }

    public int getSectionForPosition(int position) {
        return sectionForPosition.get(position);
    }

    public Object[] getSections() {
        return sectionsList.toArray();
    }
}