無法填充的ListView時用ArrayAdapter

Question

我在下面的行得到一個空指針異常，彷彿我指的是TextView的不能被發現找到的TextView：

   descriptor.setText("Single"); 

我檢查了ID字段和它在代碼和XML中完全一樣，我不確定在適配器的其他位置是否有錯誤。

logcat的

06-02 23:24:08.903 11160-11160/com.example.albert.betterapp E/AndroidRuntime﹕ FATAL EXCEPTION: main 
 
    Process: com.example.albert.betterapp, PID: 11160 
 
    java.lang.NullPointerException 
 
      at com.example.albert.betterapp.DisplayAllBets$MyListAdapter.getView(DisplayAllBets.java:464) 
 
      at android.widget.AbsListView.obtainView(AbsListView.java:2733) 
 
      at android.widget.ListView.measureHeightOfChildren(ListView.java:1274) 
 
      at android.widget.ListView.onMeasure(ListView.java:1186) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410) 
 
      at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) 
 
      at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719) 
 
      at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
 
      at android.support.v7.internal.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:124) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.support.v7.internal.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:444) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1410) 
 
      at android.widget.LinearLayout.measureVertical(LinearLayout.java:695) 
 
      at android.widget.LinearLayout.onMeasure(LinearLayout.java:588) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5365) 
 
      at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
 
      at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2505) 
 
      at android.view.View.measure(View.java:17396) 
 
      at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2175) 
 
      at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1316) 
 
      at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1513) 
 
      at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1200) 
 
      at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6401) 
 
      at android.view.Choreographer$CallbackRecord.run(Choreographer.java:803) 
 
      at android.view.Choreographer.doCallbacks(Choreographer.java:603) 
 
      at android.view.Choreographer.doFrame(Choreographer.java:573) 
 
      at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:789) 
 
      at android.os.Handler.handleCallback(Handler.java:733) 
 
      at android.os.Handler.dispatchMessage(Handler.java:95) 
 
      at android.os.Looper.loop(Looper.java:157) 
 
      at android.app.ActivityThread.main(ActivityThread.java:5335) 
 
      at java.lang.reflect.Method.invokeNative(Native Method) 
 
      at java.lang.reflect.Method.invoke(Method.java:515) 
 
      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265) 
 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081) 
 
      at dalvik.system.NativeStart.main(Native Method)

ADAPTER

private class MyListAdapter extends ArrayAdapter<BetDisplayer> { 
 
     public MyListAdapter() { 
 
      super(DisplayAllBets.this,R.layout.activity_singletotalbet,listwriter); 
 
     } 
 
     @Override 
 
     public View getView(int position,View convertView, ViewGroup parent) { 
 
      View itemView = convertView; 
 
      if (itemView == null) { 
 
       itemView = getLayoutInflater().inflate(R.layout.activity_singletotalbet,parent,false); 
 
      } 
 
      BetDisplayer currentwriter = listwriter.get(position); 
 
      Log.d("TESTING", currentwriter.getSelections()); 
 
      Log.d("TESTING2", currentwriter.getSelections()); 
 
      String selections = currentwriter.getSelections(); 
 
      int numberofselections = 0; 
 
      for(int i=0; i<selections.length(); i++) { 
 
       if(selections.charAt(i) == '/') { 
 
        numberofselections++; 
 
       } 
 
      } 
 
      if (numberofselections == 1) { 
 
       TextView descriptor = (TextView) findViewById(R.id.no); 
 
       descriptor.setText("Single"); 
 
      } else if (numberofselections == 2) { 
 
       TextView descriptor = (TextView) findViewById(R.id.no); 
 
       descriptor.setText("Double"); 
 
      } else if (numberofselections == 3) { 
 
       TextView descriptor = (TextView) findViewById(R.id.no); 
 
       descriptor.setText("Treble"); 
 
      } else { 
 
       TextView descriptor = (TextView) findViewById(R.id.no); 
 
       descriptor.setText("Accumulator" + "(" + numberofselections + ")"); 
 
      } 
 
      TextView status = (TextView) itemView.findViewById(R.id.status); 
 
      status.setText(currentwriter.getStatus()); 
 
      return itemView; 
 
     } 
 
    } 
 
    private void PopulateList() { 
 
     ArrayAdapter<BetDisplayer> adapter = new MyListAdapter(); 
 
     final ListView list = (ListView) findViewById(R.id.betslistviews); 
 
     list.setAdapter(adapter); 
 
    } 
 

 
      }

Answer 1

因爲，TextView descriptor是部分（從R.layout.activity_singletotalbet），因此訪問使用itemView

類似的參考，

TextView descriptor = (TextView) itemView.findViewById(R.id.no);