java - Fast scroll large letter thumb preview not appearing

Question

I'm trying to get the fast scroll pop up containing the large letter to appear when I the fast scroll feature in my list (just like in the image below), but for some reason it won't appear. I've consulted various tutorials but it still doesn't seem to work + I'm not sure if code is missing or some code is in the wrong place. All help would be appreciated.

strings.xml

<resources>
    <string name="app_name">World</string>

    <string name="action_search">Search</string>

    <string name="search_hint">Continent name</string>

    <string name="item0">Azerbaijan</string>
    <string name="item1">Bosnia &amp; Herzegovina</string>
    <string name="item2">Brazil</string>
    <string name="item3">China</string>
    <string name="item4">Denmark</string>
    <string name="item5">France</string>
    <string name="item6">Hungary</string>
    <string name="item7">Italy</string>
    <string name="item8">Japan</string>
    <string name="item9">Lithuania</string>
    <string name="item10">Luxembourg</string>
    <string name="item11">Malta</string>
    <string name="item12">Monaco</string>
    <string name="item13">Norway</string>
    <string name="item14">Portugal</string>
    <string name="item15">Thailand</string>
    <string name="item16">Singapore</string>
    <string name="item17">South Korea</string>
    <string name="item18">Sweden</string>
    <string name="item19">United Kingdom</string>
    <string name="item20">United States</string>


    <string name="item0_description">Item 0 description</string>
    <string name="item1_description">Item 1 description</string>
    <string name="item2_description">Item 2 description</string>
    <string name="item3_description">Item 3 description</string>
    <string name="item4_description">Item 4 description</string>
    <string name="item5_description">Item 5 description</string>
    <string name="item6_description">Item 6 description</string>
    <string name="item7_description">Item 7 description</string>
    <string name="item8_description">Item 8 description</string>
    <string name="item9_description">Item 9 description</string>
    <string name="item10_description">Item 10 description</string>
    <string name="item11_description">Item 11 description</string>
    <string name="item12_description">Item 12 description</string>
    <string name="item13_description">Item 13 description</string>
    <string name="item14_description">Item 14 description</string>
    <string name="item15_description">Item 15 description</string>
    <string name="item16_description">Item 16 description</string>
    <string name="item17_description">Item 17 description</string>
    <string name="item18_description">Item 18 description</string>
    <string name="item19_description">Item 19 description</string>
    <string name="item20_description">Item 20 description</string>

    <string-array name="items">
        //item 0    <item>@string/item0</item>
        //item 1    <item>@string/item1</item>
        //item 2    <item>@string/item2</item>
        //item 3    <item>@string/item3</item>
        //item 4    <item>@string/item4</item>
        //item 5    <item>@string/item5</item>
        //item 6    <item>@string/item6</item>
        //item 7    <item>@string/item7</item>
        //item 8    <item>@string/item8</item>
        //item 9    <item>@string/item9</item>
        //item 10    <item>@string/item10</item>
        //item 11    <item>@string/item11</item>
        //item 12    <item>@string/item12</item>
        //item 13    <item>@string/item13</item>
        //item 14    <item>@string/item14</item>
        //item 15    <item>@string/item15</item>
        //item 16    <item>@string/item16</item>
        //item 17    <item>@string/item17</item>
        //item 18    <item>@string/item18</item>
        //item 19    <item>@string/item19</item>
        //item 20    <item>@string/item20</item>
    </string-array>

    <string-array name="item_descriptions">
        //item 0    <item>@string/item0_description</item>
        //item 1    <item>@string/item1_description</item>
        //item 2    <item>@string/item2_description</item>
        //item 3    <item>@string/item3_description</item>
        //item 4    <item>@string/item4_description</item>
        //item 5    <item>@string/item5_description</item>
        //item 6    <item>@string/item6_description</item>
        //item 7    <item>@string/item7_description</item>
        //item 8    <item>@string/item8_description</item>
        //item 9    <item>@string/item9_description</item>
        //item 10    <item>@string/item10_description</item>
        //item 11    <item>@string/item11_description</item>
        //item 12    <item>@string/item12_description</item>
        //item 13    <item>@string/item13_description</item>
        //item 14    <item>@string/item14_description</item>
        //item 15    <item>@string/item15_description</item>
        //item 16    <item>@string/item16_description</item>
        //item 17    <item>@string/item17_description</item>
        //item 18    <item>@string/item18_description</item>
        //item 19    <item>@string/item19_description</item>
        //item 20    <item>@string/item20_description</item>
    </string-array>

</resources>

FragmentCountries.java

    public class FragmentCountries extends ListFragment implements SearchView.OnQueryTextListener {

    private CountriesListAdapter mAdapter;

    public FragmentCountries() {
        // Required empty constructor
    }

    public static FragmentCountries newInstance() {
        return new FragmentCountries();
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_countries, container, false);
        setHasOptionsMenu(true);
        initialize(view);
        return view;
    }

    List<Countries> list = new ArrayList<Countries>();
    private void initialize(View view) {
        String[] items = getActivity().getResources().getStringArray(R.array.country_names);
        String[] itemDescriptions = getActivity().getResources().getStringArray(R.array.country_descriptions);
        for (int n = 0; n < items.length; n++){
            Countries countries = new Countries();
            countries.setID();
            countries.setName(items[n]);
            countries.setDescription(itemDescriptions[n]);
            list.add(countries);
        }

        mAdapter = new CountriesListAdapter(list, getActivity());
        setListAdapter(mAdapter);
    }

    @Override
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
        // Set up search view
        inflater.inflate(R.menu.menu_countries, menu);
        MenuItem item = menu.findItem(R.id.action_search);
        SearchView searchView = (SearchView) MenuItemCompat.getActionView(item);
        searchView.setIconifiedByDefault(true);
        searchView.clearAnimation();
        searchView.setOnQueryTextListener(this);
        searchView.setQueryHint(getResources().getString(R.string.search_hint));

        View close = searchView.findViewById(R.id.search_close_btn);
        close.setBackgroundResource(R.drawable.ic_action_content_clear);
    }

    @Override
    public boolean onQueryTextSubmit(String newText) {
        return false;
    }

    @Override
    public boolean onQueryTextChange(String newText) {
        mAdapter.getFilter().filter(newText);
        return false;
    }


    @Override
    public int getPositionForSection(int section) {
        return alphaIndexer.get(sections[section]);
    }

    @Override
    public int getSectionForPosition(int position) {
        return 0;
    }

    @Override
    public Object[] getSections() {
        return sections;
    }
}

CountriesListAdapter.java

public class CountriesListAdapter extends BaseAdapter implements Filterable, SectionIndexer {

    private String mSections = "#ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private List<Countries> mData;
    private List<Countries> mFilteredData;
    private LayoutInflater mInflater;
    private ItemFilter mFilter;

    public CountriesListAdapter (List<Countries> data, Context context) {
        mData = data;
        mFilteredData = new ArrayList(mData);
        mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @Override
    public int getCount() {
        return mFilteredData.size();
    }

    @Override
    public String getItem(int position) {
        return mFilteredData.get(position).getName();
    }

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ViewHolder holder;
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.list_item_dualline, parent, false);
            holder = new ViewHolder();

            holder.title = (TextView) convertView.findViewById(R.id.item_name);
            holder.description = (TextView) convertView.findViewById(R.id.item_description);

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        holder.title.setText(mFilteredData.get(position).getName());
        holder.description.setText(mFilteredData.get(position).getDescription());

        return convertView;
    }

    @Override
    public Filter getFilter() {
        if (mFilter == null) {
            mFilter = new ItemFilter();
        }
        return mFilter;
    }

    /**
     * View holder
     */
    static class ViewHolder {
        private TextView title;
        private TextView description;
    }

    private class ItemFilter extends Filter {
        @Override
        protected FilterResults performFiltering(CharSequence constraint) {
            FilterResults results = new FilterResults();

            if (TextUtils.isEmpty(constraint)) {
                results.count = mData.size();
                results.values = new ArrayList(mData);
            } else {
                //Create a new list to filter on
                List<Countries> resultList = new ArrayList<Countries>();
                for (Countries str : mData) {
                    if (str.getName().toLowerCase().contains(constraint

Answer 1

Replace the setupSections() in your MainListAdapter with this code:

    private void setupSections() {

        String initial = "";
        List<String> sections = new ArrayList<String>();
        mSectionsIndexedByPosition = new int[mFilteredData.size()];
        mPositionsIndexedBySection = new int[mFilteredData.size()];

        int section = 0;
        for (int pos = 0; pos < mFilteredData.size(); pos++) {
            Main country = mFilteredData.get(pos);
            if (initial.charAt(0) != country.getContinent().charAt(0)) {
                initial = country.getContinent().substring(0, 1);
                section = sections.size();
                sections.add(initial);
                mPositionsIndexedBySection[section] = pos;
                mSectionsIndexedByPosition[pos] = section;
            } else {
                mSectionsIndexedByPosition[pos] = section;
            }
        }
        mSections = sections.toArray();
        mPositionsIndexedBySection = Arrays.copyOf(mPositionsIndexedBySection, mSections.length);

    }

Regarding the background to the index letter, you are confusing the preview background with the thumb. The thumb is the element that moves along the track. The file you call orange_fastscroll_thumb.xml is actually a preview background and not a thumb. If you change the name to orange_fastscroll_preview_bg you can set it like this:

<style name="OrangeTheme" parent="AppTheme">
    <item name="android:fastScrollPreviewBackgroundRight">@drawable/orange_fastscroll_preview_bg</item>
    <item name="android:fastScrollOverlayPosition">atThumb</item>
</style>

Apparently, the way Google coded the fast scroll code, you can't directly style the thumb and the track. You can try a couple of suggestions in this question.