創建方法ORRLite例外集

Question

創建數據庫和表傳遞successfulyl。數據庫處理器類的 我的onCreate（）：

public void onCreate(SQLiteDatabase db, ConnectionSource connectionSource) 
    { 
     try 
     { 

      TableUtils.createTable(connectionSource, Category.class); 
      TableUtils.createTable(connectionSource, Level.class); 
      DataParsing a = new DataParsing(); 
      a.fillCategories(); 
      Log.i(DatabaseHandler.class.getName(), "created new entries in onCreate: "); 
     } 
     catch (SQLException e){ 
      Log.e(TAG, "error creating DB " + DATABASE_NAME); 
      throw new RuntimeException(e); 
     } catch (JSONException e) { 
      // TODO Auto-generated catch block 
      e.printStackTrace(); 
     } 

    } 

我從網絡服務中獲取數據JSON和與GSON解析它。數據在fillcategories（）方法中成功填充類數據。然後，我希望把所有的數據到數據庫ORMLite在saveContacts（）方法：

public class DataParsing { 
    private static String KEY_STATUS = "status"; 
    private static String KEY_MESSAGE = "message"; 
    private static String KEY_CATEGORIES = "categories"; 
    private static String KEY_DATA = "data"; 
    private DatabaseHandler databaseHandler; 
    private Context _context; 
    public void fillCategories() throws JSONException, SQLException 
    { UserFunctions userFunction = new UserFunctions(); 
     JSONObject json = userFunction.loginUser("shurko@ukr.net", "123456"); 
     JSONObject data = json.getJSONObject(KEY_DATA); 
     // getting categories 
     JSONArray categories = new JSONArray(); 
     categories = data.getJSONArray(KEY_CATEGORIES); 
     Gson gson = new Gson(); 
     JsonParser parser = new JsonParser(); 
     JsonArray array = parser.parse(categories.toString()).getAsJsonArray(); 
     Type listType = new TypeToken<List<Category>>() {}.getType(); 
     List<Category> tasks = new ArrayList<Category>(); 
     tasks = gson.fromJson(array.toString(), listType); 

     saveContacts(tasks); 

    } 

    public void saveContacts(List<Category> contacts) throws SQLException 
     { 

      OrmLiteSqliteOpenHelper dbHelper= DatabaseHandler.getInstance(_context); 
      Dao<Category, Integer> daoContact=dbHelper.getDao(Category.class); 

      QueryBuilder<Category, Integer> queryBuilder = daoContact.queryBuilder(); 
      Log.i("dao",queryBuilder.selectColumns("title").prepare().toString()); 


      for (Category contact : contacts) { 
       Log.i("dao",contact.toString()); 
       HelperFactory.GetHelper().getCategoryDao().create(contact); 
      } 

     } 


} 

，並獲得集上...創建（接觸）行異常：

FATAL EXCEPTION: main 
java.lang.NullPointerException 
    at com.library.DataParsing.saveContacts(DataParsing.java:61) 
at com.library.DataParsing.fillCategories(DataParsing.java:45) 
    at com.library.DatabaseHandler.onCreate(DatabaseHandler.java:85) 
    at com.j256.ormlite.android.apptools.OrmLiteSqliteOpenHelper.onCreate(OrmLiteSqliteOpenHelper.java:169) 
    at android.database.sqlite.SQLiteOpenHelper.getWritableDatabase(SQLiteOpenHelper.java:126) 
    at com.j256.ormlite.android.AndroidConnectionSource.getReadWriteConnection(AndroidConnectionSource.java:63) 
    at com.j256.ormlite.android.AndroidConnectionSource.getReadOnlyConnection(AndroidConnectionSource.java:51) 
    at com.j256.ormlite.stmt.StatementExecutor.buildIterator(StatementExecutor.java:202) 
    at com.j256.ormlite.stmt.StatementExecutor.query(StatementExecutor.java:155) 
    at com.j256.ormlite.stmt.StatementExecutor.queryForAll(StatementExecutor.java:113) 
    at com.j256.ormlite.dao.BaseDaoImpl.queryForAll(BaseDaoImpl.java:237) 
    at com.assignmentexpert.LoginActivity$1.onClick(LoginActivity.java:97) 
    at android.view.View.performClick(View.java:2485) 
    at android.view.View$PerformClick.run(View.java:9080) 
    at android.os.Handler.handleCallback(Handler.java:587) 
    at android.os.Handler.dispatchMessage(Handler.java:92) 
    at android.os.Looper.loop(Looper.java:123) 
    at android.app.ActivityThread.main(ActivityThread.java:3687) 
    at java.lang.reflect.Method.invokeNative(Native Method) 
    at java.lang.reflect.Method.invoke(Method.java:507) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:625) 
    at dalvik.system.NativeStart.main(Native Method) 

爲什麼它發生了嗎？

Answer 1

問題通過將我的活動的上下文傳遞給OrmLiteSqliteOpenHelper解決。我用這樣的類來維持通過應用程序生命週期對數據庫的訪問：

public class ApplicationMemory extends Application{ 

    @Override 
    public void onCreate() { 
     super.onCreate(); 
     HelperFactory.SetHelper(getApplicationContext()); 
    } 
    @Override 
    public void onTerminate() { 
     HelperFactory.ReleaseHelper(); 
     super.onTerminate(); 
    } 
} 

和

public class HelperFactory { 
private static DatabaseHandler databaseHelper; 

    public static DatabaseHandler GetHelper(){ 
     return databaseHelper; 
    } 

public static void SetHelper(Context context){ 
     databaseHelper = OpenHelperManager.getHelper(context,DatabaseHandler.class); 
    } 

public static void ReleaseHelper(){ 
     OpenHelperManager.releaseHelper(); 
     databaseHelper = null; 
    } 
    } 

如果數據庫處理器 - 類，這是從OrmLiteSqliteOpenHelper延伸並在我的問題描述。