これはアンドロイドのSqliteHelperのシングルトンを行う正しい方法ですか？

Question

私はアンドロイドにSqliteHelperのための適切なシングルトンアクセスを書き留めようとしました。私はここで何かを逃しているかどうかはわからないが、最終版を形成するためにここやそこからビットと作品を得た。

public class DatabaseHelper extends SQLiteOpenHelper { 

    private static final String DATABASE_NAME = "EffiaSoft"; 
    private static final int DATABASE_VERSION = 1; 
    private static SQLiteOpenHelper sInstance; 
    private Semaphore semaphore = new Semaphore(1); 
    private Context mCxt; 

    /** 
    * Constructor should be private to prevent direct instantiation. 
    * make call to static method "getInstance()" instead. 
    */ 
    private DatabaseHelper(Context context) { 
     super(context, DATABASE_NAME, null, DATABASE_VERSION); 
     this.mCxt = context; 
    } 

    public static synchronized SQLiteOpenHelper getInstance(Context context) { 
     if (sInstance == null) { 
      sInstance = new DatabaseHelper(context.getApplicationContext()); 
     } 
     return sInstance; 
    } 

    private static <T> void setFields(Cursor cursor, T returnObject, Field[] declaredFields, String[] cursorColumns) throws IllegalAccessException { 
     for (Field declaredField : declaredFields) { 
      String fieldName = declaredField.getName(); 
      boolean hasColumn = false; 
      for (String columnName : cursorColumns) { 
       if (columnName.equals(fieldName)) 
        hasColumn = true; 
       else 
        continue; 
       break; 
      } 
      if (hasColumn) { 
       declaredField.setAccessible(true); 
       int columnIndex = cursor.getColumnIndex(fieldName); 
       if (columnIndex >= 0) { 
        if (declaredField.getType() == Character.TYPE) { 
         String value = cursor.getString(columnIndex); 
         if (!ValidationHelper.isNullOrEmpty(value) && value.length() == 1) { 
          char c = value.charAt(0); 
          declaredField.set(returnObject, c); 
         } 
        } else if (declaredField.getType() == Short.TYPE) { 
         declaredField.set(returnObject, cursor.getShort(columnIndex)); 
        } else if (declaredField.getType() == Integer.TYPE) { 
         declaredField.set(returnObject, cursor.getInt(columnIndex)); 
        } else if (declaredField.getType() == Long.TYPE) { 
         declaredField.set(returnObject, cursor.getLong(columnIndex)); 
        } else if (declaredField.getType() == Float.TYPE) { 
         declaredField.set(returnObject, cursor.getFloat(columnIndex)); 
        } else if (declaredField.getType() == Double.TYPE) { 
         declaredField.set(returnObject, cursor.getDouble(columnIndex)); 
        } else if (declaredField.getType() == Boolean.TYPE) { 
         String temp = cursor.getString(columnIndex); 
         declaredField.setBoolean(returnObject, temp.equalsIgnoreCase("Y")); 
        } else if (Date.class.equals(declaredField.getType())) { 
         if (!ValidationHelper.isNullOrEmpty(cursor.getString(columnIndex))) { 
          Date date = ValueFormatter.formatDateTime(cursor.getString(columnIndex)); 
          declaredField.set(returnObject, date); 
         } 
        } else if (BigDecimal.class.equals(declaredField.getType())) { 
         declaredField.set(returnObject, BigDecimal.valueOf(cursor.getDouble(columnIndex))); 
        } else { 
         declaredField.set(returnObject, cursor.getString(columnIndex)); 
        } 
       } 
      } 

     } 
    } 

    private void Disconnect() { 
     semaphore.release(); 
    } 

    private void Connect() { 
     try { 
      semaphore.acquire(); 
     } catch (InterruptedException e) { 
      LogHelper.writeExceptionLog(e); 
     } 
    } 

    @Override 
    public void onCreate(SQLiteDatabase db) { 

    } 

    public <T> ArrayList<T> getData(Context context, String tableName, String columnName, String filterCondition, String orderBy, 
            String groupBy, Class<T> type, SQLiteDatabase database) { 

     Connect(); 
     ArrayList<T> arrayList = null; 
     try { 
      if (context != null && !ValidationHelper.isNullOrEmpty(tableName)) { 
       SQLiteDatabase db; 
       if (database == null) { 
        db = getWritableDatabase(); 
       } else 
        db = database; 
       arrayList = new ArrayList<>(); 
       if (db != null) { 
        StringBuilder selectQuery = new StringBuilder(); 
        selectQuery.append("SELECT "); 
        if (columnName != null && columnName.length() > 0) 
         selectQuery.append(columnName); 
        else 
         selectQuery.append("*"); 
        selectQuery.append(" FROM "); 
        selectQuery.append(tableName); 
        if (!ValidationHelper.isNullOrEmpty(filterCondition)) { 
         selectQuery.append(" WHERE "); 
         selectQuery.append(filterCondition); 
        } 
        if (!ValidationHelper.isNullOrEmpty(orderBy)) { 
         selectQuery.append(" ORDER BY "); 
         selectQuery.append(orderBy); 
        } 
        if (!ValidationHelper.isNullOrEmpty(groupBy)) { 
         selectQuery.append(" GROUP BY "); 
         selectQuery.append(groupBy); 
        } 
        Cursor cursor; 
        cursor = db.rawQuery(selectQuery.toString(), null); 
        if (cursor != null) { 
         String[] cursorColumn = cursor.getColumnNames(); 
         if (cursor.moveToFirst()) { 
          do { 
           T returnObject = type.newInstance(); 
           Class<?> returnClass = returnObject.getClass(); 
           if (!returnClass.getSuperclass().equals(Object.class)) { 
            setFields(cursor, returnObject, returnClass.getSuperclass().getDeclaredFields(), cursorColumn); 
           } 
           setFields(cursor, returnObject, returnClass.getDeclaredFields(), cursorColumn); 
           arrayList.add(returnObject); 
          } while (cursor.moveToNext()); 
         } 

        } 
       } 
      } 
     } catch (Exception e) { 
      LogHelper.writeExceptionLog(e); 
     } finally { 
      Disconnect(); 
     } 
     return arrayList; 
    } 

    @Override 
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { 

    } 

    @Override 
    protected void finalize() throws Throwable { 
     this.close(); 
     super.finalize(); 
     Disconnect(); 
    } 
} 

Answer 1

あなたはこのように定義する必要があります。あなたがそうであるようにパラメータに基づいて、単一のインスタンスをキャッシュすることは適切ではありません

DatabaseHelper db = DatabaseHelper.getInstance(context);