的OnClick與自定義適配器和ListView

Question

看着許多其他職位，並嘗試了幾種變化，但至今沒有運氣...

掌握定義所以下面的自定義列表適配器NPE：

public ListView tripList; 
.... 
@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 

    .... 

     // build a listView adapter 
     Log.i(LOGTAG,"About to create listView..."); 
     tripList = (ListView) findViewById(android.R.id.list); 
     Log.i(LOGTAG,"ListView created..."); 

     Log.i(LOGTAG,"About to create adapter..."); 
     tripAdapter = new tripListAdapter(this, tripCur); 
     setListAdapter(tripAdapter); 

    } 

    setContentView(R.layout.activity_trip_display); 

...和適配器具有這樣的：

// custom list adaptor class 
private class tripListAdapter extends CursorAdapter { 

    //private final Cursor dataC; 
    private final LayoutInflater vi; 

    public tripListAdapter(Context con, Cursor c) { 
     // super constructor thingy 
     super(con, c); 
     //dataC = c; 
     vi = LayoutInflater.from(con); 

    } 

@Override 
    public View getView (int position, View tripView, ViewGroup parent){ 

     Log.i(LOGTAG,"In getView..."); 
     // Create a message handling object as an anonymous class. 
     //mTripClickHandler = new OnItemClickListener() { 

// NPE ERROR ON THIS NEXT LINE (line 228): 
     tripList.setOnItemClickListener(new OnItemClickListener() { 
      public void onItemClick(AdapterView<?> parent, View v, int position, long id) { 
       // Do something in response to the click 
       // Enable other buttons 
       togBtns(true); 

的logcat：

06-13 09:47:49.195: I/WIBBLE(864): ListView created... 
06-13 09:47:49.195: I/WIBBLE(864): About to create adapter... 
06-13 09:47:49.285: I/WIBBLE(864): OnResume with this many rows returned by cursor: 3 
06-13 09:47:49.285: I/WIBBLE(864): In the loop, so cursor is not null.... 
06-13 09:47:49.375: I/WIBBLE(864): In getView... 
06-13 09:47:49.387: D/AndroidRuntime(864): Shutting down VM 
06-13 09:47:49.387: W/dalvikvm(864): threadid=1: thread exiting with uncaught exception (group=0x414c4700) 
06-13 09:47:49.505: E/AndroidRuntime(864): FATAL EXCEPTION: main 
06-13 09:47:49.505: E/AndroidRuntime(864): java.lang.NullPointerException 
06-13 09:47:49.505: E/AndroidRuntime(864): at com.example.myfirstapp.DisplayTripsActivity$tripListAdapter.getView(DisplayTripsActivity.java:228) 
06-13 09:47:49.505: E/AndroidRuntime(864): at android.widget.AbsListView.obtainView(AbsListView.java:2177) 
06-13 09:47:49.505: E/AndroidRuntime(864): at android.widget.ListView.measureHeightOfChildren(ListView.java:1247) 
06-13 09:47:49.505: E/AndroidRuntime(864): at android.widget.ListView.onMeasure(ListView.java:1159) 
06-13 09:47:49.505: E/AndroidRuntime(864): at android.view.View.measure(View.java:15848) 
06-13 09:47:49.505: E/AndroidRuntime(864): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008) 

任何建議感激地收到。

編輯：如果我更換：

//tripList = (ListView) findViewById(android.R.id.list); 

有：

tripList = getListView(); 

...我繼續前進（見維布勒消息），但得到另一個NPE，但似乎是在一些常規的系統：

06-13 10:26:49.825: I/WIBBLE(934): About to create listView... 
06-13 10:26:49.865: I/WIBBLE(934): ListView created... 
06-13 10:26:49.865: I/WIBBLE(934): About to create adapter... 
06-13 10:26:49.945: I/WIBBLE(934): OnResume with this many rows returned by cursor: 3 
06-13 10:26:49.945: I/WIBBLE(934): In the loop, so cursor is not null.... 
06-13 10:26:50.035: I/WIBBLE(934): In getView... 
06-13 10:26:50.035: I/WIBBLE(934): Leaving getView... 
06-13 10:26:50.035: D/AndroidRuntime(934): Shutting down VM 
06-13 10:26:50.035: W/dalvikvm(934): threadid=1: thread exiting with uncaught exception (group=0x414c4700) 
06-13 10:26:50.185: E/AndroidRuntime(934): FATAL EXCEPTION: main 
06-13 10:26:50.185: E/AndroidRuntime(934): java.lang.NullPointerException 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.AbsListView.obtainView(AbsListView.java:2179) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.ListView.measureHeightOfChildren(ListView.java:1247) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.ListView.onMeasure(ListView.java:1159) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.view.View.measure(View.java:15848) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5008) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1404) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.LinearLayout.measureHorizontal(LinearLayout.java:1052) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.widget.LinearLayout.onMeasure(LinearLayout.java:590) 
06-13 10:26:50.185: E/AndroidRuntime(934): at android.view.View.measure(View.java:15848) 

...和很多其他行，沒有引用我的代碼。

Answer 1

您不應該從Adapter設置onItemClickListener。 Adapter只關心創建單個列表項視圖。在視圖膨脹後，從Activity（或Fragment）中設置onItemClickListener。

看起來您目前沒有設置活動視圖，這就是tripList ListView爲NULL的原因。使用setContentView(R.layout.your_layout)將視圖設置爲xml佈局。

您可能需要發佈大部分代碼。這是一個活動還是片段？你在擴展一個基本的Activity/Fragment，或者其他的ListActivity/ListFragment。我不知道，因爲你正在訪問Android的R檔，而不是你自己（android.R.id.list VS R.id.list）

更新

好吧，我已經回答了我的問題。您正在使用ListActivity（或ListFragment），這就是您使用Android的R文件的原因。我會將其更改爲getListView()而不是findViewById。我仍然會將setOnItemClickListener移到新的NPE例外，因爲這是正確的方法。

Answer 2

在分配您的tripView變量ListView，需要使用：

tripList = (ListView) findViewById(android.R.id.list); 

嘗試改變這一行：

tripList = (ListView) findViewById(R.id.list); 

而是搜索android.R爲正確項（其中它可能沒有按」的t退出），在構建項目時生成的R文件中查找ListView項目。

確保在運行之前重建項目。