NULL-Zeiger-Ausnahme auf Service-Objekt

Question

Ich versuche, Google Task mit meiner Anwendung zu synchronisieren. Dafür habe ich eine Klasse namens GTaskSyncer erstellt, wo ich Methoden erstellt habe, um Aufgabendetails zu erhalten.

Ich möchte diese Methoden von UI aufrufen. Jetzt zum Test habe ich eine Klasse erstellt, die AsyncTask in diesem ich habe Methode in doInbackground genannt erweitert.

Dies habe ich in der Haupttätigkeit aufgerufen.

Jetzt bekomme ich eine Nullzeiger Ausnahme für Service-Objekt in GTaskSyncer.

Haupttätigkeit

public class MainActivity extends AppCompatActivity { 
    GoogleAccountCredential mCredential; 
    private TextView mOutputText; 
    ProgressDialog mProgress; 

    static final int REQUEST_ACCOUNT_PICKER = 1000; 
    static final int REQUEST_AUTHORIZATION = 1001; 
    static final int REQUEST_GOOGLE_PLAY_SERVICES = 1002; 
    private static final String PREF_ACCOUNT_NAME = "accountName"; 
    private static final String[] SCOPES = { TasksScopes.TASKS }; 
    public com.google.api.services.tasks.Tasks mService = null; 
    /** 
    * Create the main activity. 
    * @param savedInstanceState previously saved instance data. 
    */ 
    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     LinearLayout activityLayout = new LinearLayout(this); 
     LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(
       LinearLayout.LayoutParams.MATCH_PARENT, 
       LinearLayout.LayoutParams.MATCH_PARENT); 
     activityLayout.setLayoutParams(lp); 
     activityLayout.setOrientation(LinearLayout.VERTICAL); 
     activityLayout.setPadding(16, 16, 16, 16); 

     ViewGroup.LayoutParams tlp = new ViewGroup.LayoutParams(
       ViewGroup.LayoutParams.WRAP_CONTENT, 
       ViewGroup.LayoutParams.WRAP_CONTENT); 

     mOutputText = new TextView(this); 
     mOutputText.setLayoutParams(tlp); 
     mOutputText.setPadding(16, 16, 16, 16); 
     mOutputText.setVerticalScrollBarEnabled(true); 
     mOutputText.setMovementMethod(new ScrollingMovementMethod()); 
     activityLayout.addView(mOutputText); 

     mProgress = new ProgressDialog(this); 
     mProgress.setMessage("Calling Google Tasks API ..."); 

     Button sync = new Button(this); 

     sync.setText("Sync"); 

     setContentView(activityLayout); 

     // Initialize credentials and service object. 
     SharedPreferences settings = getPreferences(Context.MODE_PRIVATE); 
     mCredential = GoogleAccountCredential.usingOAuth2(
       getApplicationContext(), Arrays.asList(SCOPES)) 
       .setBackOff(new ExponentialBackOff()) 
       .setSelectedAccountName(settings.getString(PREF_ACCOUNT_NAME, null)); 

     HttpTransport transport = AndroidHttp.newCompatibleTransport(); 
     JsonFactory jsonFactory = JacksonFactory.getDefaultInstance(); 
     mService = new com.google.api.services.tasks.Tasks.Builder(
       transport, jsonFactory, mCredential) 
       .setApplicationName("Google Tasks API Android Quickstart") 
       .build(); 
    } 


    /** 
    * Called whenever this activity is pushed to the foreground, such as after 
    * a call to onCreate(). 
    */ 
    @Override 
    protected void onResume() { 
     super.onResume(); 
     if (isGooglePlayServicesAvailable()) { 
      refreshResults(); 
     } else { 
      mOutputText.setText("Google Play Services required: " + 
        "after installing, close and relaunch this app."); 
     } 
    } 

    /** 
    * Called when an activity launched here (specifically, AccountPicker 
    * and authorization) exits, giving you the requestCode you started it with, 
    * the resultCode it returned, and any additional data from it. 
    * @param requestCode code indicating which activity result is incoming. 
    * @param resultCode code indicating the result of the incoming 
    *  activity result. 
    * @param data Intent (containing result data) returned by incoming 
    *  activity result. 
    */ 
    @Override 
    protected void onActivityResult(
      int requestCode, int resultCode, Intent data) { 
     super.onActivityResult(requestCode, resultCode, data); 
     switch(requestCode) { 
      case REQUEST_GOOGLE_PLAY_SERVICES: 
       if (resultCode != RESULT_OK) { 
        isGooglePlayServicesAvailable(); 
       } 
       break; 
      case REQUEST_ACCOUNT_PICKER: 
       if (resultCode == RESULT_OK && data != null && 
         data.getExtras() != null) { 
        String accountName = 
          data.getStringExtra(AccountManager.KEY_ACCOUNT_NAME); 
        if (accountName != null) { 
         mCredential.setSelectedAccountName(accountName); 
         SharedPreferences settings = 
           getPreferences(Context.MODE_PRIVATE); 
         SharedPreferences.Editor editor = settings.edit(); 
         editor.putString(PREF_ACCOUNT_NAME, accountName); 
         editor.apply(); 
        } 
       } else if (resultCode == RESULT_CANCELED) { 
        mOutputText.setText("Account unspecified."); 
       } 
       break; 
      case REQUEST_AUTHORIZATION: 
       if (resultCode != RESULT_OK) { 
        chooseAccount(); 
       } 
       break; 
     } 

     super.onActivityResult(requestCode, resultCode, data); 
    } 

    /** 
    * Attempt to get a set of data from the Google Tasks API to display. If the 
    * email address isn't known yet, then call chooseAccount() method so the 
    * user can pick an account. 
    */ 
    private void refreshResults() { 
     if (mCredential.getSelectedAccountName() == null) { 
      chooseAccount(); 
     } else { 
      if (isDeviceOnline()) { 
       new TestAsyncTask(mCredential).execute(); 
      } else { 
       mOutputText.setText("No network connection available."); 
      } 
     } 
    } 
    /** 
    * Starts an activity in Google Play Services so the user can pick an 
    * account. 
    */ 
    private void chooseAccount() { 
     startActivityForResult(
       mCredential.newChooseAccountIntent(), REQUEST_ACCOUNT_PICKER); 
    } 

    /** 
    * Checks whether the device currently has a network connection. 
    * @return true if the device has a network connection, false otherwise. 
    */ 
    private boolean isDeviceOnline() { 
     ConnectivityManager connMgr = 
       (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE); 
     NetworkInfo networkInfo = connMgr.getActiveNetworkInfo(); 
     return (networkInfo != null && networkInfo.isConnected()); 
    } 

    /** 
    * Check that Google Play services APK is installed and up to date. Will 
    * launch an error dialog for the user to update Google Play Services if 
    * possible. 
    * @return true if Google Play Services is available and up to 
    *  date on this device; false otherwise. 
    */ 
    private boolean isGooglePlayServicesAvailable() { 
     final int connectionStatusCode = 
       GooglePlayServicesUtil.isGooglePlayServicesAvailable(this); 
     if (GooglePlayServicesUtil.isUserRecoverableError(connectionStatusCode)) { 
      showGooglePlayServicesAvailabilityErrorDialog(connectionStatusCode); 
      return false; 
     } else if (connectionStatusCode != ConnectionResult.SUCCESS) { 
      return false; 
     } 
     return true; 
    } 

    /** 
    * Display an error dialog showing that Google Play Services is missing 
    * or out of date. 
    * @param connectionStatusCode code describing the presence (or lack of) 
    *  Google Play Services on this device. 
    */ 
    void showGooglePlayServicesAvailabilityErrorDialog(
      final int connectionStatusCode) { 
     Dialog dialog = GooglePlayServicesUtil.getErrorDialog(
       connectionStatusCode, 
       MainActivity.this, 
       REQUEST_GOOGLE_PLAY_SERVICES); 
     dialog.show(); 
    } 

} 

TestAsyncTask

public class TestAsyncTask extends AsyncTask<Void, Void, List<TaskList>>{ 

    private com.google.api.services.tasks.Tasks mService = null; 
    private Exception mLastError = null; 
    private MainActivity activity; 
    private com.google.api.services.tasks.Tasks client = null; 

    public TestAsyncTask(GoogleAccountCredential credential) { 
     HttpTransport transport = AndroidHttp.newCompatibleTransport(); 
     JsonFactory jsonFactory = JacksonFactory.getDefaultInstance(); 
     mService = new com.google.api.services.tasks.Tasks.Builder(
       transport, jsonFactory, credential) 
       .setApplicationName("Google Tasks API Android Quickstart") 
       .build(); 

    } 
    protected List<TaskList> doInBackground(Void... params) { 

     GTaskSyncer gTaskSyncer = new GTaskSyncer(activity); 

     List<TaskList> result = new ArrayList<>(); 

     try { 

      result = gTaskSyncer.getAllTaskList(); 

     } catch (IOException e) { 

      Toast.makeText(activity,"IO Exception",Toast.LENGTH_SHORT).show(); 
     } 
     return result; 
    } 
} 

GTaskSyncer

public class GTaskSyncer 
{ 

    final MainActivity activity; 
    final com.google.api.services.tasks.Tasks mService; 


    GTaskSyncer(MainActivity activity) { 
     this.activity = activity; 
     mService = activity.mService; 
    } 

    public List<TaskList> getAllTaskList() throws IOException 
    { 
     List<TaskList> result = new ArrayList<TaskList>(); 

     TaskLists taskLists = mService.tasklists().list().execute(); 

     for (TaskList taskList : taskLists.getItems()) { 

       result.add(taskList); 
     } 

     return result; 

    } 


    public TaskList createList() throws IOException 
    { 

     TaskList taskList = new TaskList(); 

     taskList = activity.mService.tasklists().insert(taskList).execute(); 

     return taskList; 
    } 

    public Task createTask(String listId) throws IOException 
    { 

     Task task = new Task(); 

     task = activity.mService.tasks().insert(listId, task).execute(); 

     return task; 
    } 

    public Task getTask(String listId,String taskId) throws IOException 
    { 

     Task task = activity.mService.tasks().get(listId, taskId).execute(); 

     return task; 
    } 

    public List<Task> getTaskList(String listId) throws IOException 
    { 
     List<Task> result = new ArrayList<Task>(); 

     List<Task> tasks = mService.tasks().list(listId).execute().getItems(); 

     if (tasks != null) { 

      for (Task task : tasks) { 

       result.add(task); 
      } 
     } else { 

      Toast.makeText(activity,"No tasks.",Toast.LENGTH_SHORT).show(); 
     } 

     return result; 
    } 

} 

Bitte helfen ..

Answer 1

Sie dies nicht initialisiert haben private MainActivity activity; Und Sie verwenden diese Instanz von GTaskSyncer

GTaskSyncer gTaskSyncer = new GTaskSyncer(activity); 

zu erstellen So ist es bei weitergegeben hier wird:

GTaskSyncer(MainActivity activity) { 
    this.activity = activity; // null 
    mService = activity.mService; // exception 
} 

Und schließlich ist es an vielen Orten, die Sie verwenden, die exception verursacht.

taskList = activity.mService.tasklists().insert(taskList).execute(); 

Versuchen Sie, den Konstruktor zu ändern:

public TestAsyncTask(GoogleAccountCredential credential, MainActivity activity) { 
    HttpTransport transport = AndroidHttp.newCompatibleTransport(); 
    JsonFactory jsonFactory = JacksonFactory.getDefaultInstance(); 
    mService = new com.google.api.services.tasks.Tasks.Builder(
      transport, jsonFactory, credential) 
      .setApplicationName("Google Tasks API Android Quickstart") 
      .build(); 
    this.activity = activity; 
} 

Und es so nennen:

new TestAsyncTask(mCredential, MainActivity.this).execute(); 

Answer 2

seine besser Konstruktor

GTaskSyncer(MainActivity activity,com.google.api.services.tasks.Tasks mService) { 
     this.activity = activity; 
     this.mService = mService; 
}