java - ExpandableList 不在屏幕上显示列表

Question

我正在尝试实现 search Activity，其中包含ExpandableList在不同组中显示的歌曲、专辑、艺术家。

查询一切正常，适配器正在获得正确的搜索结果。但是列表没有显示在屏幕上。

这是代码：

搜索活动：

public class SearchActivity extends Activity implements TextWatcher {

    private EditText etSearchBar;
    private ExpandableListView lvExpSearchResult;
    private SearchExpandListAdapter expand_adapter;
    private Cursor cursor;
    int columnIndex;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.search);

        etSearchBar = (EditText) findViewById(R.id.etSearchBar);
        lvExpSearchResult = (ExpandableListView) findViewById(R.id.lvExpSearchResult);

        etSearchBar.addTextChangedListener(this);
    }

    @Override
    public void beforeTextChanged(CharSequence paramCharSequence,
            int paramInt1, int paramInt2, int paramInt3) {
    }

    @Override
    public void onTextChanged(CharSequence paramCharSequence, int paramInt1,
            int paramInt2, int paramInt3) {
        ArrayList<ExpandListGroup> groups = new ArrayList<ExpandListGroup>();
        ArrayList<String> result = null;

        ExpandListGroup trackSection = new ExpandListGroup();
        result = getQueryResult(MediaStore.Audio.Media.TITLE);
        trackSection.setName("Tracks");
        trackSection.setItems(result);

        ExpandListGroup albumSection = new ExpandListGroup();
        result = getQueryResult(MediaStore.Audio.Media.ALBUM);
        albumSection.setName("Albums");
        albumSection.setItems(result);

        ExpandListGroup artistSection = new ExpandListGroup();
        result = getQueryResult(MediaStore.Audio.Media.ARTIST);
        artistSection.setName("Artist");
        artistSection.setItems(result);

        groups.add(trackSection);
        groups.add(albumSection);
        groups.add(artistSection);

        expand_adapter = new SearchExpandListAdapter(this, groups);
        Toast.makeText(this, "onTextChanged", Toast.LENGTH_SHORT).show();
    }

    @Override
    public void afterTextChanged(Editable paramEditable) {
        lvExpSearchResult.setAdapter(expand_adapter);
        Toast.makeText(this, "afterTextChanged", Toast.LENGTH_SHORT).show();
        Toast.makeText(this, ((Integer)expand_adapter.getChildrenCount(1)).toString(), Toast.LENGTH_SHORT).show();
    }

    private ArrayList<String> getQueryResult(String columnToDisplay) {
        String searchQuery = etSearchBar.getText().toString();
        ArrayList<String> result = new ArrayList<String>();

        if (searchQuery.length() > 0) {
            String[] projection = { MediaStore.Audio.Media._ID,
                    MediaStore.Audio.Media.DISPLAY_NAME,
                    MediaStore.Audio.Media.DATA, MediaStore.Audio.Media.TITLE,
                    MediaStore.Audio.Media.ARTIST, MediaStore.Audio.Media.ALBUM };

            String queryString = MediaStore.Audio.Media.IS_MUSIC + "!=" + 0
                    + " AND " + columnToDisplay + " LIKE \"%" + searchQuery
                    + "%\"";

            cursor = managedQuery(MediaStore.Audio.Media.EXTERNAL_CONTENT_URI,
                    projection, queryString, null, columnToDisplay
                            + " COLLATE NOCASE");

            for (cursor.moveToFirst(); !cursor.isAfterLast(); cursor
                    .moveToNext()) {
                columnIndex = cursor.getColumnIndexOrThrow(columnToDisplay);
                result.add(cursor.getString(columnIndex));
            }
        } else {
            result.clear();
        }
        return result;
    }
}

适配器类：

public class SearchExpandListAdapter extends BaseExpandableListAdapter {

    Context context;
    ArrayList<ExpandListGroup> groups;

    public SearchExpandListAdapter(Context c, ArrayList<ExpandListGroup> groups) {
        this.context = c;
        this.groups = groups;
    }

    public void addItem(String item, String group) {
        if (!groups.contains(group)) {
            Toast.makeText(context,
                    "Error while adding item in group " + group,
                    Toast.LENGTH_SHORT).show();
            return;
        }
        int index = groups.indexOf(group);
        ArrayList<String> children = groups.get(index).getItems();
        children.add(item);
        groups.get(index).setItems(children);
    }

    @Override
    public Object getChild(int groupPosition, int childPosition) {
        ArrayList<String> children = groups.get(groupPosition).getItems();
        String child = children.get(childPosition);
        return child;
    }

    @Override
    public long getChildId(int groupPosition, int childPosition) {
        return childPosition;
    }

    @Override
    public View getChildView(int groupPosition, int childPosition,
            boolean isLastChild, View view, ViewGroup parent) {
        String child = (String) getChild(groupPosition, childPosition);
        if (view == null) {
            LayoutInflater inflator = (LayoutInflater) context
                    .getSystemService(context.LAYOUT_INFLATER_SERVICE);
            view = inflator.inflate(R.layout.expandlist_child_item, null);
        }
        TextView tvChild = (TextView) view.findViewById(R.id.tvChild);
        tvChild.setText(child);
        return view;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        ArrayList<String> children = groups.get(groupPosition).getItems();
        return children.size();
    }

    @Override
    public Object getGroup(int groupPosition) {
        return groups.get(groupPosition);
    }

    @Override
    public int getGroupCount() {
        return groups.size();
    }

    @Override
    public long getGroupId(int groupPosition) {
        return groupPosition;
    }

    @Override
    public View getGroupView(int groupPosition, boolean isLastChild, View view,
            ViewGroup parent) {
        ExpandListGroup group = (ExpandListGroup) getGroup(groupPosition);
        if (view == null) {
            LayoutInflater inflator = (LayoutInflater) context
                    .getSystemService(context.LAYOUT_INFLATER_SERVICE);
            view = inflator.inflate(R.layout.expandlist_group_item, null);
        }
        TextView tvGroup = (TextView) view.findViewWithTag(R.id.tvGroup);
        tvGroup.setText(group.getName());
        return view;
    }

    @Override
    public boolean hasStableIds() {
        return true;
    }

    @Override
    public boolean isChildSelectable(int paramInt1, int paramInt2) {
        return true;
    }
}