android – java.lang.NullPointerException：尝试在空对象引用上调用虚方法’java.io.File com.parse.ParsePlugins.getParseDir()’

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试图从Parse加载一个类,但是一旦我启动它,应用程序就会崩溃！
这是代码： 
  1. ListView listview;
  2. List<ParSEObject> ob;
  3. ProgressDialog mProgressDialog;
  4. ArrayAdapter<String> adapter;
  5.  
  6. @Override
  7. protected void onCreate(Bundle savedInstanceState) {
  8.     super.onCreate(savedInstanceState);
  9.     setContentView(R.layout.activity_big_board);
  10.     new RemoteDataTask().execute();
  11.  
  12. }
  13.  
  14. private class RemoteDataTask extends AsyncTask<Void,Void,Void> {
  15.     @Override
  16.     protected void onPreExecute() {
  17.         super.onPreExecute();
  18.         mProgressDialog = new ProgressDialog(BigBoard.this);
  19.         mProgressDialog.setTitle("Parse.com Simple ListView Tutorial");
  20.         mProgressDialog.setMessage("Loading...");
  21.         mProgressDialog.setIndeterminate(false);
  22.         mProgressDialog.show();
  23.     }
  24.  
  25.     @Override
  26.     protected Void doInBackground(Void... params) {
  27.         // Locate the class table named "Country" in Parse.com
  28.         ParseQuery<ParSEObject> query = new ParseQuery<ParSEObject>(
  29.                 "Country");
  30.         query.orderByDescending("_created_at");
  31.         try {
  32.             ob = query.find();
  33.         } catch (ParseException e) {
  34.             Log.e("Error",e.getMessage());
  35.             e.printStackTrace();
  36.         }
  37.         return null;
  38.     }
  39.  
  40.     @Override
  41.     protected void onPostExecute(Void result) {
  42.         // Locate the listview in listview_main.xml
  43.         listview = (ListView) findViewById(R.id.listview);
  44.         // Pass the results into an ArrayAdapter
  45.         adapter = new ArrayAdapter<String>(BigBoard.this,R.layout.listview_item);
  46.         // Retrieve object "name" from Parse.com database
  47.         for (ParSEObject country : ob) {
  48.             adapter.add((String) country.get("Name"));
  49.         }
  50.         // Binds the Adapter to the ListView
  51.         listview.setAdapter(adapter);
  52.         // Close the progressdialog
  53.         mProgressDialog.dismiss();
  54.         // Capture button clicks on ListView items
  55.         listview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
  56.             @Override
  57.             public void onItemClick(AdapterView<?> parent,View view,int position,long id) {
  58.                 // Send single item click data to SingleItemView Class
  59.                 Intent i = new Intent(BigBoard.this,SingleItemView.class);
  60.                 // Pass data "name" followed by the position
  61.                 i.putExtra("name",ob.get(position).getString("name")
  62.                         .toString());
  63.                 // Open SingleItemView.java Activity
  64.                 startActivity(i);
  65.             }
  66.         });
  67.     }
  68. }

这就是我在logcat中获得的：

  1. > 10-22 20:40:18.705  12588-12872/obx.com.futurister E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #3
  2.     Process: obx.com.futurister,PID: 12588
  3.     java.lang.RuntimeException: An error occurred while executing doInBackground()
  4.             at android.os.AsyncTask$3.done(AsyncTask.java:309)
  5.             at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
  6.             at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
  7.             at java.util.concurrent.FutureTask.run(FutureTask.java:242)
  8.             at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
  9.             at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
  10.             at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
  11.             at java.lang.Thread.run(Thread.java:818)
  12.      Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.File com.parse.ParsePlugins.getParseDir()' on a null object reference
  13.             at com.parse.Parse.getParseDir(Parse.java:315)
  14.             at com.parse.ParseCorePlugins.getCurrentUserController(ParseCorePlugins.java:129)
  15.             at com.parse.ParseUser.getCurrentUserController(ParseUser.java:55)
  16.             at com.parse.ParseUser.getCurrentUserAsync(ParseUser.java:888)
  17.             at com.parse.ParseQuery.getUserAsync(ParseQuery.java:938)
  18.             at com.parse.ParseQuery$3.call(ParseQuery.java:1196)
  19.             at com.parse.ParseQuery$3.call(ParseQuery.java:1193)
  20.             at com.parse.ParseQuery.doWithRunningCheck(ParseQuery.java:1132)
  21.             at com.parse.ParseQuery.findAsync(ParseQuery.java:1193)
  22.             at com.parse.ParseQuery.findInBackground(ParseQuery.java:1161)
  23.             at com.parse.ParseQuery.find(ParseQuery.java:981)
  24.             at obx.com.futurister.BigBoard$RemoteDataTask.doInBackground(BigBoard.java:66)
  25.             at obx.com.futurister.BigBoard$RemoteDataTask.doInBackground(BigBoard.java:44)
  26.             at android.os.AsyncTask$2.call(AsyncTask.java:295)
  27.             at java.util.concurrent.FutureTask.run(FutureTask.java:237)
  28. at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
  29. at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
  30. at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
  31. at java.lang.Thread.run(Thread.java:818)
  32. 10-22 20:40:18.857  12588-12619/obx.com.futurister E/Surface﹕ getSlotFromBufferLocked: unknown buffer: 0xb3a1fb90
  33. 10-22 20:40:18.955  12588-12619/obx.com.futurister E/Surface﹕ getSlotFromBufferLocked: unknown buffer: 0xa96acbb0
  34. 10-22 20:40:18.996  12588-12588/obx.com.futurister E/WindowManager﹕ android.view.WindowLeaked: Activity obx.com.futurister.BigBoard has leaked window com.android.internal.policy.PhoneWindow$DecorView{a0f50b2 V.E...... R......D 0,0-1026,538} that was originally added here
  35.             at android.view.ViewRootImpl.<init>(ViewRootImpl.java:368)
  36.             at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:299)
  37.             at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:85)
  38.             at android.app.Dialog.show(Dialog.java:319)
  39.             at obx.com.futurister.BigBoard$RemoteDataTask.onPreExecute(BigBoard.java:56)
  40.             at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:604)
  41.             at android.os.AsyncTask.execute(AsyncTask.java:551)
  42.             at obx.com.futurister.BigBoard.onCreate(BigBoard.java:40)
  43.             at android.app.Activity.performCreate(Activity.java:6237)
  44.             at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
  45.             at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
  46.             at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
  47.             at android.app.ActivityThread.-wrap11(ActivityThread.java)
  48.             at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
  49.             at android.os.Handler.dispatchMessage(Handler.java:102)
  50.             at android.os.Looper.loop(Looper.java:148)
  51.             at android.app.ActivityThread.main(ActivityThread.java:5417)
  52.             at java.lang.reflect.Method.invoke(Native Method)
  53.             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
  54.             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

用doInBackground()方法猜测它的问题？我错过了什么吗？请帮忙,谢谢

解决方法

根据你的评论,我猜你还没有初始化Parse.
http://docs.parseplatform.org/android/guide/#local-datastore 
  1. public class App extends Application {
  2.  
  3.     @Override
  4.     public void onCreate() {
  5.         super.onCreate();
  6.  
  7.         // Enable Local Datastore.
  8.         Parse.enableLocalDatastore(this);
  9.  
  10.         // Register any ParSEObject subclass. Must be done before calling Parse.initialize()
  11.         ParSEObject.registerSubclass(YourClass.class);
  12.  
  13.         Parse.initialize(this,"APPLICATION_ID","CLIENT_KEY");    
  14.     }
  15. }

确保将App类添加到清单中

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