带有 Json 数组的 ExpandableListAdapter

Question

我正在尝试使用 ExpandableListAdapter 和 followed this tutorial 编写应用程序，但我将使用 json 对我的数据库 (MYSQL) 进行整数运算，所以我遇到了这个问题：

Caused by: java.lang.NullPointerException at 
com.example.smart_survey.ExpandableListAdapter.getGroupCount
(ExpandableListAdapter.java:71)

有人可以帮帮我吗

班级ExpandableListAdapter：

public class ExpandableListAdapter extends BaseExpandableListAdapter {

    private Context _context;
    **private List<String> _listDataHeader= null;** // header titles
    // child data in format of header title, child title
    private HashMap<String, List<String>> _listDataChild;


    public ExpandableListAdapter(Context context, List<String> listDataHeader,
                HashMap<String, List<String>> listChildData) {
        this._context = context;
        **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) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_item, null);
        }

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

        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) {
            LayoutInflater infalInflater = (LayoutInflater) this._context
                    .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            convertView = infalInflater.inflate(R.layout.list_group, null);
        }

        TextView lblListHeader = (TextView) convertView
                .findViewById(R.id.lblListHeader);
        lblListHeader.setTypeface(null, Typeface.BOLD);
        lblListHeader.setText(headerTitle);

        return convertView;
    }

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

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

}

类二维码

public class QR extends Activity {

    ExpandableListAdapter listAdapter;
    ExpandableListView expListView;
    ArrayList<String> listDataHeader;
    HashMap<String, List<String>> listDataChild;

    // Creating JSON Parser object
    JSONParser jParser = new JSONParser();


    // url to get all products list
    private static String url_all_quests = 
        "http://10.0.2.2/android_connect/listquest.php";

    // JSON Node names
    private static final String TAG_SUCCESS = "success";
    private static final String TAG_QUEST = "Question";
    private static final String TAG_REP = "Reponse";
    private static final String TAG_IDE = "idenq";
    private static final String TAG_IDQ = "idquest";
    private static final String TAG_LIBQ = "libquest";
    private static final String TAG_LIBR = "librep";


    // products JSONArray

    String idenq;
    String idquest;
    String libquest,librep;
    Button valider;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list_quest);
        Intent i = getIntent();
        idenq = i.getStringExtra(TAG_IDE);
        idquest = i.getStringExtra(TAG_IDQ);
        // get the listview
        expListView = (ExpandableListView) findViewById(R.id.list);

        // preparing list data
        new prepareListData().execute();

        listAdapter = new ExpandableListAdapter(this, listDataHeader,
                         listDataChild);

        // setting list adapter
        expListView.setAdapter(listAdapter);

        // Listview Group click listener
        expListView.setOnGroupClickListener(new OnGroupClickListener() {

            @Override
            public boolean onGroupClick(ExpandableListView parent, View v,
                    int groupPosition, long id) {
                // Toast.makeText(getApplicationContext(),
                // "Group Clicked " + listDataHeader.get(groupPosition),
                // Toast.LENGTH_SHORT).show();
                return false;
            }
        });

        // Listview Group expanded listener
        expListView.setOnGroupExpandListener(new OnGroupExpandListener() {

            @Override
            public void onGroupExpand(int groupPosition) {
                Toast.makeText(getApplicationContext(),
                        listDataHeader.get(groupPosition) + "
                                                     Expanded",
                        Toast.LENGTH_SHORT).show();
            }
        });

        // Listview Group collasped listener
        expListView.setOnGroupCollapseListener(new OnGroupCollapseListener() {

            @Override
            public void onGroupCollapse(int groupPosition) {
                Toast.makeText(getApplicationContext(),
                        listDataHeader.get(groupPosition) + " 
                                     Collapsed",
                        Toast.LENGTH_SHORT).show();

            }
        });

        // Listview on child click listener
        expListView.setOnChildClickListener(new OnChildClickListener() {

            @Override
            public boolean onChildClick(ExpandableListView parent, View v,
                    int groupPosition, int childPosition, long id) {
                // TODO Auto-generated method stub
                Toast.makeText(
                        getApplicationContext(),
                        listDataHeader.get(groupPosition)
                                + " : "
                                +  
                            listDataChild.get(listDataHeader.get(groupPosition)).
                                get(childPosition), Toast.LENGTH_SHORT)
                        .show();
                return false;
            }
        });
    }

    /*
     * Preparing the list data
     */
    class prepareListData extends AsyncTask<String, String, String> { 

        @Override
        protected String doInBackground(String... params) {
            // Building Parameters
            List<NameValuePair> params1 = new ArrayList<NameValuePair>();
            params1.add(new BasicNameValuePair("idenq", idenq));
            params1.add(new BasicNameValuePair("idquest", idquest));

            params1.add(new BasicNameValuePair("libquest", libquest));

            params1.add(new BasicNameValuePair("librep", librep));
            // getting JSON string from URL
            JSONObject json = jParser.makeHttpRequest(
                url_all_quests, "GET", params1);

            listDataHeader = new ArrayList<String>();
            listDataChild = new HashMap<String, List<String>>();
            // products found
            // Getting Array of Products
            JSONArray Question;
            try {
                Question = json.getJSONArray(TAG_QUEST);
                    // looping through All Products
                for (int i = 0; i < Question.length(); i++) {

                    // creating new HashMap
                    HashMap<String, String> map = new HashMap<String, String>();
                    // Storing each json item in variable
                    JSONObject c=Question.getJSONObject(i);
                    String libquest = c.getString(TAG_LIBQ);
                    map.put(TAG_LIBQ, libquest);

                    // Adding child data
                    listDataHeader.add(libquest);

                    // 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");
                    listDataChild.put(listDataHeader.get(i), top250); // Header, Child data
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        return null;
        }
    }
}

Answer 1

我认为您的问题是您在AsynTask 中的doInBackground 中填充了listDataHeader。我从未尝试从AsynTask 返回ArrayList，但我认为这将解决您的问题。更改 AsynTask 以返回 ArrayList 并实现 onPostExecute 以填充您的变量。在doInBackground 中，您应该填充一个局部变量，然后返回它。像这样的：

class prepareListData extends AsyncTask<String, String, ArrayList<String>> { 

    protected void onPostExecute(ArrayList<String> result) {
        listDataHeader = result;
    }
    @Override
    protected String doInBackground(String... params) {
    // ......
        return localListDataHeader;
    }
}

试试看是否能解决你的问题。