Java BaseAdapter - ArrayList作爲返回值 - NullpointerException

Question

我試圖顯示最後十個數據庫對象的ListView。如果我在標籤中顯示這些對象，一切正常，但現在我創建了一個ListView + DataAdapter，但該應用程序崩潰時出現NullPointerException。我googled了很多，但唯一的解決方案，我發現ArrayList沒有初始化=新的ArrayList（）或視圖的名稱不匹配findViewById方法，但他們都沒有在我的項目中是錯誤的。感謝您的幫助:)

MainActivity.java

public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); //res/layout/activity_main.xml Layout 
    list = (ListView) findViewById(R.id.lastpushlist); 
    list.setAdapter(new DataAdapter(this)); 

DataAdapter.java

Controller aController = new Controller(); 
Context context; 
ArrayList<SingleRow> list = aController.getLastLogs(MainActivity.regIDglobal, "10"); 

DataAdapter(Context c){ 

    context = c; 
} 

@Override 
public int getCount() { 
    // TODO Auto-generated method stub 
    return list.size(); 
} 

@Override 
public Object getItem(int position) { 
    // TODO Auto-generated method stub 
    return list.get(position); 
} 

@Override 
public long getItemId(int position) { 
    // TODO Auto-generated method stub 
    return position; 
} 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    // TODO Auto-generated method stub 
    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
    View row = inflater.inflate(R.layout.single_row, parent,false); 
    TextView Message = (TextView) row.findViewById(R.id.textView1); 
    TextView URL = (TextView) row.findViewById(R.id.textView2); 

    SingleRow temp = list.get(position); 
    Message.setText(temp.message); 
    URL.setText(temp.url); 
    return row; 
} 

Controller.java

ArrayList<SingleRow> list = new ArrayList<SingleRow>(); 
// Lots of Database Calls and get JSON Objects but for Testing i just create and add some Test Data into the list and return it. 
list.add(new SingleRow("bla","bla2")); 
return list; 

activity_main.xml中

<ListView 
    android:id="@+id/lastpushlist" 
    android:layout_height="fill_parent" 
    android:layout_width="fill_parent" > 
</ListView> 

的logcat：

02-24 12:20:23.468: D/AndroidRuntime(1475): Shutting down VM 
02-24 12:20:23.472: D/dalvikvm(1475): GC_CONCURRENT freed 440K, 19% free 2720K/3336K, paused 4ms+0ms, total 16ms 
02-24 12:20:23.476: W/dalvikvm(1475): threadid=1: thread exiting with uncaught exception (group=0xa615d908) 
02-24 12:20:23.476: E/AndroidRuntime(1475): FATAL EXCEPTION: main 
02-24 12:20:23.476: E/AndroidRuntime(1475): java.lang.RuntimeException: Unable to start activity ComponentInfo{de.fhdortmund.pushprojekt/de.fhdortmund.pushprojekt.MainActivity}: java.lang.NullPointerException 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread.access$600(ActivityThread.java:141) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.os.Handler.dispatchMessage(Handler.java:99) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.os.Looper.loop(Looper.java:137) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread.main(ActivityThread.java:5041) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at java.lang.reflect.Method.invokeNative(Native Method) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at java.lang.reflect.Method.invoke(Method.java:511) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at dalvik.system.NativeStart.main(Native Method) 
02-24 12:20:23.476: E/AndroidRuntime(1475): Caused by: java.lang.NullPointerException 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at de.fhdortmund.pushprojekt.DataAdapter.<init>(DataAdapter.java:16) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at de.fhdortmund.pushprojekt.MainActivity.onCreate(MainActivity.java:49) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.Activity.performCreate(Activity.java:5104) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144) 
02-24 12:20:23.476: E/AndroidRuntime(1475):  ... 11 more 

DataAdapter的第16行是：ArrayList的列表= aController.getLastLogs（MainActivity.regIDglobal， 「10」）; MainActivity第49行是：list.setAdapter（new DataAdapter（this））;

Answer 1

唯一可能在第16行拋出NPE的是如果aController爲null。你沒有在這個對象被創建的地方發佈代碼，所以我認爲它根本就不是。