片段中的 ExpandableListView 出错

Question

所以我设置了我的 ExpandableListView，我在我的 TextView 上得到了一个 NullPointer，它不应该 return "null".

这是我的代码：

public class HelpFragment extends Fragment {

@BindView(R.id.expandableListView)
ExpandableListView expandableListView;

public static HelpFragment newInstance() {
    HelpFragment fragment = new HelpFragment();
    return fragment;
}

ExpandableListAdapter listAdapter;
List<String> listDataHeader;
HashMap<String, List<String>> listDataChild;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.fragment_help, null);
    ButterKnife.bind(this, rootView);

    prepareListData();

    listAdapter = new ExpandableListAdapter(listDataHeader, listDataChild);
    expandableListView.setAdapter(listAdapter);

    Log.i("groups", listDataHeader.toString());
    Log.i("details", listDataChild.toString());

    return rootView;
}

private void prepareListData() {
    listDataHeader = new ArrayList<String>();
    listDataChild = new HashMap<String, List<String>>();

    // Adding child data
    listDataHeader.add("Top 250");
    listDataHeader.add("Now Showing");
    listDataHeader.add("Coming Soon..");

    // Adding child data
    List<String> top250 = new ArrayList<String>();
    top250.add("The Shawshank Redemption");
    top250.add("The Godfather");
    top250.add("The Godfather: Part II");
    top250.add("Pulp Fiction");
    top250.add("The Good, the Bad and the Ugly");
    top250.add("The Dark Knight");
    top250.add("12 Angry Men");

    List<String> nowShowing = new ArrayList<String>();
    nowShowing.add("The Conjuring Despicable Me TurboGrown Ups 2 Red 2 the Wolverine The Conjuring Despicable Me TurboGrown Ups 2 Red 2 the Wolverine");

    List<String> comingSoon = new ArrayList<String>();
    comingSoon.add("2 Guns");
    comingSoon.add("The Smurfs 2");
    comingSoon.add("The Spectacular Now");
    comingSoon.add("The Canyons");
    comingSoon.add("Europa Report");

    listDataChild.put(listDataHeader.get(0), top250); // Header, Child data
    listDataChild.put(listDataHeader.get(1), nowShowing);
    listDataChild.put(listDataHeader.get(2), comingSoon);

}

public class ExpandableListAdapter extends BaseExpandableListAdapter {

    private List<String> _listDataHeader; // header titles
    // child data in format of header title, child title
    private HashMap<String, List<String>> _listDataChild;

    public ExpandableListAdapter(List<String> listDataHeader,
                                 HashMap<String, List<String>> listChildData) {
        this._listDataHeader = listDataHeader;
        this._listDataChild = listChildData;
    }

    @Override
    public Object getChild(int groupPosition, int childPosititon) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .get(childPosititon);
    }

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

    @Override
    public View getChildView(int groupPosition, final int childPosition,
                             boolean isLastChild, View convertView, ViewGroup parent) {

        final String childText = (String) getChild(groupPosition, childPosition);

        if (convertView == null) {
            convertView = LayoutInflater.from(getActivity()).inflate(R.layout.list_item, null);
        }

        TextView txtListChild = (TextView) convertView.findViewById(R.id.expandedListItem);

        txtListChild.setText(childText);
        return convertView;
    }

    @Override
    public int getChildrenCount(int groupPosition) {
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .size();
    }

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

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

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

    @Override
    public View getGroupView(int groupPosition, boolean isExpanded,
                             View convertView, ViewGroup parent) {
        String headerTitle = (String) getGroup(groupPosition);
        if (convertView == null) {
            convertView = LayoutInflater.from(getActivity()).inflate(R.layout.expandable_list_group, null);
        }

        TextView lblListHeader = (TextView) convertView.findViewById(R.id.listExpandableTitle);
        lblListHeader.setText(headerTitle);

        return convertView;
    }

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

    @Override
    public boolean isChildSelectable(int groupPosition, int childPosition) {
        return true;
    }
}

出现错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

对于这一行：

txtListChild.setText(childText);

在 getChildView 方法中。

所以我不明白为什么它 return 对 txtListChild 来说是 null。

我怀疑 convertView 为空，但这是不可能的，因为我涵盖了这种情况。所以也许我在 covertview 上做错了，因为它在片段中。

我真的卡住了。提前致谢！

编辑：我不准确，但是当我点击一个项目时出现 Nullpointer

Answer 1

试试这个方法

if (convertView == null) {
            LayoutInflater layoutInflater = (LayoutInflater) this.context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = layoutInflater.inflate(R.layout. expandable_list_item, null);
        }

片段中的 ExpandableListView 出错

Error with a ExpandableListView in fragment

android

expandablelistview

expandablelistadapter