getListAdapter（）從ListFragment返回null，getListView工作

Question

按標題，我被堵在這個荒謬的問題

我有一個ListFragment，這裏的精簡代碼：

public class AlarmsListFragment extends ListFragment implements AbsListView.OnItemClickListener { 
    public ListAdapter mAdapter; 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     setRetainInstance(true); 

     mAdapter = new AlarmsAdapter(getActivity(), R.layout.alarm_card_item, alarmsList); 
    } 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 

     View view = inflater.inflate(R.layout.fragment_alarms_list, container, false); 

     mListView = (AbsListView) view.findViewById(android.R.id.list); 
     mListView.setAdapter(mAdapter); 

     mListView.setOnItemClickListener(this); 

     return view; 
    } 
} 

而且然後有一個活動：

public class MainActivity extends Activity implements AlarmsListFragment.OnAlarmSelectedListener { 
ListFragment mAlarmsListFragment; 
protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     FragmentManager fm = getFragmentManager(); 
     mAlarmsListFragment = (ListFragment) fm.findFragmentByTag(ALARM_LIST_TAG); 
     if (mAlarmsListFragment == null) 
     { 
      mAlarmsListFragment = new AlarmsListFragment(); 
      getFragmentManager().beginTransaction() 
        .add(R.id.listContainer, mAlarmsListFragment, ALARM_LIST_TAG) 
        .commit(); 
     } 
    } 

後來，onOptionsItemSelected，我有一些代碼，需要將項目添加到ListAdapter和無效前面的列表，所以我打電話：

AlarmsAdapter mAdapater = (AlarmsAdapter) mAlarmsListFragment.getListAdapter(); 
mAdapater.add(a); 
mAdapater.notifyDataSetChanged(); 

事情是，我得到一個NullPointerException因爲getListAdapter（）返回null，而getListView（）工作正常..什麼可能導致這個錯誤？

Answer 1

你需要調用setListAdapter您ListFragment，即：

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    setRetainInstance(true); 

    mAdapter = new AlarmsAdapter(getActivity(), R.layout.alarm_card_item, alarmsList); 

    setListAdapter(mAdapter); 
} 

你不需要調用setAdapter您的ListView。 ListFragment將處理它。