SQLite查詢和LocationListener中的NullPointerException

我想獲取用戶的位置並將其與我的數據庫中的位置進行比較，這是我提出的代碼，但它仍然無法正常工作，它給了我這個空指針異常行：SQLite查詢和LocationListener中的NullPointerException

Cursor cursor = database.query(MySQLiteHelper.TABLE_Hotel, 
      new String[]{MySQLiteHelper.H_ID, MySQLiteHelper.H_Name, MySQLiteHelper.H_Longitude, MySQLiteHelper.H_Latitude}, null, null, null, null, null);

這是全班同學：

public class locationFinder extends ListActivity implements LocationListener { 


    List<Hotel> hotelsInRange = new ArrayList<Hotel>(); 
    MySQLiteHelper mySQL; 
    SQLiteDatabase database; 
    EgyptDataSource datasource; 
    Location locObject; 
    String loc; 
    double lat; 
    double longi; 
    @Override 
     public void onCreate(Bundle savedInstanceState) { 
      super.onCreate(savedInstanceState); 

      LocationManager locManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE); 
      locManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, this); 
      } 

    public void onLocationChanged(Location location) { 
     // TODO Auto-generated method stub 

     setListOfHotelsInRange(location); 
    } 


    private void setListOfHotelsInRange(Location userLocation) 
    { 
     Cursor cursor = database.query(MySQLiteHelper.TABLE_Hotel, 
       new String[]{MySQLiteHelper.H_ID, MySQLiteHelper.H_Name, MySQLiteHelper.H_Longitude, MySQLiteHelper.H_Latitude}, null, null, null, null, null); 


     while(cursor.moveToNext()) 
     { 
      double longi = cursor.getDouble(cursor.getColumnIndex(MySQLiteHelper.H_Longitude)); 
      double lat = cursor.getDouble(cursor.getColumnIndex(MySQLiteHelper.H_Latitude)); 

      Location currentHotelLocation = new Location("Current Hotel"); 
      currentHotelLocation.setLatitude(lat); 
      currentHotelLocation.setLongitude(longi); 

      double distanceInMeters = userLocation.distanceTo(currentHotelLocation); 

      if (distanceInMeters < 500000000) 
      { 
       //hotel is in range 
       Hotel hotel = new Hotel(); 
       hotel.set_id(cursor.getInt(0)); 
       hotel.setName(cursor.getString(0)); 
       hotelsInRange.add(hotel); 
      } 

     } 
     ArrayAdapter<Hotel> adapter = new ArrayAdapter<Hotel>(this, 
       android.R.layout.simple_list_item_1, hotelsInRange); 
       setListAdapter(adapter); 

    } 

    public void onProviderDisabled(String provider) { 
     // TODO Auto-generated method stub 

    } 

    public void onProviderEnabled(String provider) { 
     // TODO Auto-generated method stub 

    } 

    public void onStatusChanged(String provider, int status, Bundle extras) { 
     // TODO Auto-generated method stub 

    } 

}

這是logcat的：

06-22 22:55:32.984: E/AndroidRuntime(2378): FATAL EXCEPTION: main 
06-22 22:55:32.984: E/AndroidRuntime(2378): java.lang.NullPointerException 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at egypt.interfaceAct.locationFinder.setListOfHotelsInRange(locationFinder.java:99) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at egypt.interfaceAct.locationFinder.onLocationChanged(locationFinder.java:93) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.location.LocationManager$ListenerTransport._handleMessage(LocationManager.java:191) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.location.LocationManager$ListenerTransport.access$000(LocationManager.java:124) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.location.LocationManager$ListenerTransport$1.handleMessage(LocationManager.java:140) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.os.Handler.dispatchMessage(Handler.java:99) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.os.Looper.loop(Looper.java:143) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at android.app.ActivityThread.main(ActivityThread.java:4914) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at java.lang.reflect.Method.invokeNative(Native Method) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at java.lang.reflect.Method.invoke(Method.java:521) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 
06-22 22:55:32.984: E/AndroidRuntime(2378):  at dalvik.system.NativeStart.main(Native Method)

來源

2012-06-22 MahaK

你從來沒有實例化數據庫...，你應該從SQLiteOpenHelper獲得SQLiteDatabase，你實例化SQLiteOpen Helper，並返回數據庫getWritableDatabase（） – DGomez

這就是爲什麼你的遊標返回null，並調用moveToNext（）引發NPE。 – Guardanis

對不起，你能更清楚嗎？我應該添加什麼代碼？ – MahaK

成員database從不初始化。您應該在locationFinder活動的onCreate()內初始化它。像@DGomez提到

public void onCreate(Bundle icicle){ 
    super.onCreate(icicle); 

    mySQL = new MySQLiteHelper(); 
    database = mySQL.getWriteableDatabase(); 

    LocationManager locManager = (LocationManager) etSystemService(Context.LOCATION_SERVICE); 
    locManager.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, this); 
}

來源

2012-06-22 21:31:32

由於DGomez你沒有得到你的數據庫的實例用於查詢。

假設MySQLiteHelper延伸SQLiteOpenHelper做類似下面的...

在onCreate(...)方法...

mySQL = new MySQLiteHelper(this, "my-database-name", null, 1);

然後在您的setListOfHotelsInRange(...)方法您查詢數據庫之前做...

database = mySQL.getWriteableDatabase();

來源

2012-06-22 21:31:57 Squonk

SQLite查詢和LocationListener中的NullPointerException

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