修复Tab +使用ListView滑动

Question

我正在做一个有多个标签的应用，每个标签都有自己的活动。在将代码加载到一个活动的列表之后;仍然没有看到listview。 这是我的代码，有人请帮忙：

public class BillsActivity extends ListActivity {
private ProgressDialog pDialog;
String mUrl = BayadCenterConstants.BAYAD_URL_BILLERS;

JSONParsers jsonParser = new JSONParsers(); 
ArrayList<HashMap<String, String>> billerList;
JSONArray billers = null;

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

    /*
     * Check network connection here
     */

    billerList = new ArrayList<HashMap<String, String>>();

    new LoadBillers().execute();

}

class LoadBillers extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        pDialog = new ProgressDialog(BillsActivity.this);
        pDialog.setMessage("Downlaoding list ...");
        pDialog.setIndeterminate(false);
        pDialog.setCancelable(false);
        pDialog.show();
    }

    protected String doInBackground(String... args) {
        List<NameValuePair> params = new ArrayList<NameValuePair>();

        String json = jsonParser.getBillers(mUrl, params);

        Log.d("Billers JSON: ", "> " + json);

        try {              
            billers = new JSONArray(json);

            if (billers != null) {
                for (int i = 0; i < billers.length(); i++) {
                    JSONObject c = billers.getJSONObject(i);

                    String id = c.getString("bid");
                    String name = c.getString("name");
                    String status = c.getString("status");
                    String date_added = c.getString("date_added");

                    HashMap<String, String> map = new HashMap<String, String>();

                    map.put("bid", id);
                    map.put("name", name);
                    map.put("status", status);
                    map.put("date_added", date_added);

                    billerList.add(map);
                }
            }else{
                Log.d("Billers: ", "null");
            }

        } catch (JSONException e) {
            e.printStackTrace();
        }

        return null;
    }

    protected void onPostExecute(String file_url) {
        pDialog.dismiss();

        runOnUiThread(new Runnable() {
            public void run() {

                ListAdapter adapter = new SimpleAdapter(
                        BillsActivity.this, billerList,
                        R.layout.tab_child_bills_list_row, new String[] { "bid", "name", "status", 
                                "date_added" }, new int[] { R.id.txtBillerID, R.id.txtBillerName, 
                                R.id.txtBillerStatus, R.id.txtBillerDateAdded });

                setListAdapter(adapter);
            }
        });

    }

}

此活动只是以标签+滑动方式保存的活动的一部分。 我错过了我的代码吗？