空指针异常上下文为空

Question

     @Override
     protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_postlist);
      ListView listView = (ListView) this.findViewById(R.id.postListView);
        PostItemAdapter itemAdapter = new PostItemAdapter(this,
        R.layout.list, listData);
        //this.accessWebService();
        listView.setAdapter(itemAdapter);

     }




     03-15 16:11:12.104: E/AndroidRuntime(844): FATAL EXCEPTION: main
03-15 16:11:12.104: E/AndroidRuntime(844): java.lang.RuntimeException: Unable to start activity ComponentInfo{ie.ucc.bis.is4432calculator/ie.ucc.bis.is4432calculator.secondActivity}: java.lang.NullPointerException
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.ActivityThread.access$1500(ActivityThread.java:117)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.os.Handler.dispatchMessage(Handler.java:99)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.os.Looper.loop(Looper.java:123)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.ActivityThread.main(ActivityThread.java:3683)
03-15 16:11:12.104: E/AndroidRuntime(844):  at java.lang.reflect.Method.invokeNative(Native Method)
03-15 16:11:12.104: E/AndroidRuntime(844):  at java.lang.reflect.Method.invoke(Method.java:507)
03-15 16:11:12.104: E/AndroidRuntime(844):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
03-15 16:11:12.104: E/AndroidRuntime(844):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
03-15 16:11:12.104: E/AndroidRuntime(844):  at dalvik.system.NativeStart.main(Native Method)
03-15 16:11:12.104: E/AndroidRuntime(844): Caused by: java.lang.NullPointerException
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.widget.ArrayAdapter.getCount(ArrayAdapter.java:291)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.widget.ListView.setAdapter(ListView.java:454)
03-15 16:11:12.104: E/AndroidRuntime(844):  at ie.ucc.bis.is4432calculator.secondActivity.onCreate(secondActivity.java:42)
03-15 16:11:12.104: E/AndroidRuntime(844):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

03-15 16:11:12.104: E/AndroidRuntime(844): 在 android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611) 03-15 16:11:12.104: E/AndroidRuntime(844): ... 11 更多

如何使用intent作为适配器请帮忙.............

这些都是错误

Answer 1

listData 可能是null。这就是ArrayAdapter.getCount() 抛出 NPE 的最可能原因。