應用程序試圖在模擬器上運行[Android的工作室]崩潰

Question

我試圖運行在模擬器但每次它崩潰的時候， 的應用程序，我得到的是造成這個錯誤：

[ 「在顯示java.lang.NullPointerException（android.support.v4.app.backstackrecord.doAddOp（Backstackrecord.java:394）」]

我什麼都試過，但我知道我仍然在stucked！ 我猜我錯過了一些代碼，但我不知道它是什麼！

這裏是鏈接所有的logcat Full logcat 這裏是MainActivity.java類：

public class MainActivity extends ActionBarActivity { 

    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 
     if (savedInstanceState == null) 
     { 
      getSupportFragmentManager().beginTransaction() 
       .add(R.id.container, new ForecastFragment() 
         .Commit()); 
      } 
     } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     // Inflate the menu; this adds items to the action bar if it is present. 
     getMenuInflater().inflate(R.menu.main, menu); 
     return true; 
    } 

    @Override 
    public boolean onOptionsItemSelected(MenuItem item) { 
     // Handle action bar item clicks here. The action bar will 
     // automatically handle clicks on the Home/Up button, so long 
     // as you specify a parent activity in AndroidManifest.xml. 
     int id = item.getItemId(); 
     if (id == R.id.action_settings) { 
      return true; 
     } 
     return super.onOptionsItemSelected(item); 
    } 

    /** 
    * A placeholder fragment containing a simple view. 
    */ 
    public ForecastFragment Commit() { 
     return null; 
    } 

      HttpURLConnection urlConnection = null; 
      BufferedReader reader = null; 

      String forecastJsonStr = null; 
    } 

這裏是ForecastFragment.java類：

public class ForecastFragment extends Fragment { 

     public ForecastFragment() { 
     } 

     @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 
      setHasOptionsMenu(true); 
     } 


     public void onCreateOptionMenu(Menu menu, MenuInflater inflater) { 
      inflater.inflate(R.menu.forecastfragment, menu); 
     } 


     public boolean onOptionItemSelected(MenuItem item) { 
      int id = item.getItemId(); 
      if (id == R.id.action_refresh) { 
       FetchWeatherTask weatherTask = new FetchWeatherTask(); 
       weatherTask.execute("94043"); 
       return true; 
      } 
      return super.onOptionsItemSelected(item); 
     } 

     @Override 
     public View onCreateView(LayoutInflater inflater, ViewGroup container, 
           Bundle savedInstanceState) { 

      String[] data = { 
        "Today - Sunny - 88/63", 
        "Tomorrow - foggy - 70/46", 
        "weds - Cloudy - 72/63", 
        "Thurs - Rainy - 64/51", 
        "Fri - Foggy - 70/46", 
        "Sat - Sunny - 76/68" 
      }; 

      List<String> weekForecast = new ArrayList<String>(
        Arrays.asList(data)); 


      ArrayAdapter<String> mForecastAdapter = 

      new ArrayAdapter<String>(
        getActivity(), 
        R.layout.list_item_forecast, 
        R.id.list_item_forecast_textview, 
        weekForecast); 

      View rootView = inflater.inflate(R.layout.fragment_main, container, false); 

      ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast); 
      listView.setAdapter(mForecastAdapter); 

      return rootView; 
     } 

     public ForecastFragment Commit() { 
      return null; 
     } 

     public class FetchWeatherTask extends AsyncTask<String, Void, Void> { 
      private final String LOG_TAG = FetchWeatherTask.class.getSimpleName(); 

      private String getReadableDataString(long time) { 
       Date date = new Date(time * 1000); 
       SimpleDateFormat format = new SimpleDateFormat("E, MMM d"); 
       return format.format(date).toString(); 
      } 

      protected String[] doInBackGround(String... params) { 

       if (params.length == 0) { 
        return null; 
       } 

       HttpURLConnection urlConnection = null; 
       BufferedReader reader = null; 

       String forecastJsonStr = null; 

       String format = "json"; 
       String units = "metric"; 
       int numDays = 7; 


       try { 
        final String FORECAST_BASE_URL = 
          "http://api.openweathermap.org/data/2.5/forecast/daily?"; 
        final String QUERY_PARAM = "q"; 
        final String FORMAT_param = "MODE"; 
        final String UNITS_param = "UNITS"; 
        final String DAYS_param = "CNT"; 

        Uri builtUri = Uri.parse(FORECAST_BASE_URL).buildUpon() 
          .appendQueryParameter(QUERY_PARAM, params[0]) 
          .appendQueryParameter(FORMAT_param, format) 
          .appendQueryParameter(UNITS_param, format) 
          .appendQueryParameter(DAYS_param, Integer.toString(numDays)) 
          .build(); 

        URL url = new URL(builtUri.toString()); 
        Log.v(LOG_TAG, "Built Uri " + builtUri.toString()); 


        urlConnection = (HttpURLConnection) url.openConnection(); 
        urlConnection.setRequestMethod("GET"); 
        urlConnection.connect(); 

        InputStream inputStream = urlConnection.getInputStream(); 
        StringBuffer buffer = new StringBuffer(); 
        if (inputStream == null) { 
         return null; 

        } 

        reader = new BufferedReader(new InputStreamReader(inputStream)); 

        String line; 
        while ((line = reader.readLine()) != null) { 

         buffer.append(line + "\n"); 
        } 

        if (buffer.length() == 0) { 
         return null; 
        } 


        forecastJsonStr = buffer.toString(); 

        Log.v(LOG_TAG, "Forecast JSON String: " + forecastJsonStr); 

       } catch (IOException e) { 
        Log.e(LOG_TAG, "Error", e); 
        return null; 

       } finally { 
        if (urlConnection != null) { 
         urlConnection.disconnect(); 
        } 
        if (reader != null) { 
         try { 
          reader.close(); 
         } catch (final IOException e) { 
          Log.e(LOG_TAG, "Error closing stream", e); 
         } 
        } 
       } 
       return getWeatherDataFromJson(forecastJsonStr, numDays); 

      } 



      @Override 
      protected Void doInBackground(String... params) { 
       return null; 
      } 
     } 

     public String[] getWeatherDataFromJson(String forecastJsonStr, int numDays) { 
      return new String[0]; 
     } 
    } 

謝謝！

Answer 1

您的NullPointerException位於onCreate中MainActivity的第20行。你似乎已經把一些括號不對勁的地方：

getSupportFragmentManager().beginTransaction() 
      .add(R.id.container, new ForecastFragment() 
        .Commit()); 

的Commit()上的片段來完成。它必須是

getSupportFragmentManager() 
    .beginTransaction() 
    .add(R.id.container, new ForecastFragment()) 
    .commit(); 

如果這不能解決，您可以調試對象並檢查哪一個爲空。