是否有重構此SQLite數據庫處理程序的有效方法？

Question

我正在處理我的第一個Android應用程序，並且遇到了一個問題，我正在重複使用很多代碼片段來執行數據庫連接。我看到自己一遍又一遍地重寫相同的try/catch語句，但是我遇到了處理它的好方法。請看看這段代碼，你是否看到我缺少如何重構這個的明顯方式？

正如你所看到的那樣，這些方法通常只有1或2條線差異。下面是一個示例（所有其他try/catch代碼都是類似的）：

遊標cursor = dbAdapter.fetchReceipts（timeFrom，timeTo）;

Communicator.java

public ArrayList<Receipt> getReceipts(int limit) 
{ 
    ArrayList<Receipt> receiptList = null; 
    DbAdapter dbAdapter = new DbAdapter(context); 

    try 
    { 
     dbAdapter.open(); 
     Cursor cursor = dbAdapter.fetchReceipts(limit); 

     if (cursor != null) 
     { 
      receiptList = buildReceiptList(cursor); 
     } 

     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 
    return receiptList; 
} 

public ArrayList<Receipt> getReceipts(long timeFrom, long timeTo) 
{ 
    ArrayList<Receipt> receiptList = null; 
    DbAdapter dbAdapter = new DbAdapter(context); 

    try 
    { 
     dbAdapter.open(); 
     Cursor cursor = dbAdapter.fetchReceipts(timeFrom, timeTo); 

     if (cursor != null) 
     { 
      receiptList = buildReceiptList(cursor); 
     } 

     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 
    return receiptList; 
} 


public Receipt getLatestReceipt() 
{ 
    Receipt receipt = null; 
    Cursor cursor = null; 
    DbAdapter dbAdapter = new DbAdapter(context); 

    try 
    { 
     dbAdapter.open(); 
     cursor = dbAdapter.fetchLastReceipt(); 

     if (cursor.getCount() > 0) 
     { 
      receipt = buildReceipt(cursor); 
     } 

     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 
    return receipt; 
} 

public ArrayList<Receipt> searchReceipts(String query) 
{ 
    ArrayList<Receipt> receiptList = null; 
    DbAdapter dbAdapter = new DbAdapter(context); 

    try 
    { 
     dbAdapter.open(); 
     Cursor cursor = dbAdapter.searchReceiptName(query); 

     if (cursor != null) 
     { 
      receiptList = buildReceiptList(cursor); 
     } 

     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 

    return receiptList; 
} 

public boolean updateReceipt(Receipt receipt) 
{ 
    DbAdapter dbAdapter = new DbAdapter(context); 
    boolean result = false; 
    try 
    { 
     dbAdapter.open(); 
     result = dbAdapter.updateReceipt(receipt.getId(), receipt.getName(), receipt.getPhoto(), receipt.getTimestamp(), 
       receipt.getLocationLat(), receipt.getLocationLong(), receipt.getSum(), receipt.getTax(), receipt.getComment()); 
     showResult(result); 
     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 
    return result; 
} 

private boolean insertReceipt(Receipt receipt) 
{ 
    boolean result = false; 
    DbAdapter dbAdapter = new DbAdapter(context); 
    try 
    { 
     dbAdapter.open(); 
     result = dbAdapter.createReceipt(receipt.getName(), receipt.getPhoto(), receipt.getTimestamp(), receipt.getLocationLat(), 
       receipt.getLocationLong(), receipt.getSum(), receipt.getTax(), receipt.getComment()); 
     showResult(result); 
     dbAdapter.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 
    return result; 
} 

DBAdapter.java

public Cursor fetchReceipt(long rowId) throws SQLException 
{ 

    Cursor cursor = db 
      .query(true, DATABASE_TABLE_RECEIPTS, new String[] { KEY_ROWID, KEY_NAME, KEY_PHOTO, KEY_TIMESTAMP, KEY_LOCATION_LAT, 
        KEY_LOCATION_LONG, KEY_SUM, KEY_TAX, KEY_COMMENT }, KEY_ROWID + "=" + rowId, null, null, null, null, null); 
    if (cursor != null) 
    { 
     cursor.moveToFirst(); 
    } 
    return cursor; 

} 

public Cursor fetchReceipts(long timeFrom, long timeTo) 
{ 
    Cursor cursor = db.query(true, DATABASE_TABLE_RECEIPTS, new String[] { KEY_ROWID, KEY_NAME, KEY_PHOTO, KEY_TIMESTAMP, 
      KEY_LOCATION_LAT, KEY_LOCATION_LONG, KEY_SUM, KEY_TAX, KEY_COMMENT }, KEY_TIMESTAMP + ">" + timeFrom + " AND " 
      + KEY_TIMESTAMP + "<" + timeTo, null, null, null, KEY_TIMESTAMP + " DESC", null); 
    if (cursor != null) 
    { 
     cursor.moveToFirst(); 
    } 
    return cursor; 
} 

public Cursor fetchLastReceipt() 
{ 
    Cursor cursor = db.query(true, DATABASE_TABLE_RECEIPTS, new String[] { KEY_ROWID, KEY_NAME, KEY_PHOTO, KEY_TIMESTAMP, 
      KEY_LOCATION_LAT, KEY_LOCATION_LONG, KEY_SUM, KEY_TAX, KEY_COMMENT }, null, null, null, null, KEY_ROWID + " DESC", "1"); 
    if (cursor != null) 
    { 
     cursor.moveToFirst(); 
    } 
    return cursor; 
} 

public Cursor searchReceiptName(String query) 
    { 
     Cursor cursor = db.query(DATABASE_TABLE_RECEIPTS, new String[] { KEY_ROWID, KEY_NAME, KEY_PHOTO, KEY_TIMESTAMP, KEY_LOCATION_LAT, 
       KEY_LOCATION_LONG, KEY_SUM, KEY_TAX, KEY_COMMENT }, KEY_NAME + " LIKE ?", new String[] { "%" + query + "%" }, null, null, 
       null); 
     if (cursor != null) 
     { 
      cursor.moveToFirst(); 
     } 
     return cursor; 
    } 

Answer 1

首先，打開數據庫的時候，我會更好地使用這樣的：

if (db == null || !db.isOpen()) { 
db = getWritableDatabase(); //getReadableDatabase(); 
} 

，它會照顧你創建或打開數據庫，以防尚未完成。

對於方法的第一塊我想清楚地去somethink像：

public ArrayList<Receipt> searchReceipts(String query, DbAdapter _db, Cursor cursor) 
{ 
    ArrayList<Receipt> receiptList = null; 

    try 
    { 
     _db.open(); 

     if (cursor != null) 
     { 
      receiptList = buildReceiptList(cursor); 
     } 

     _db.close(); 
    } 
    catch (SQLException e) 
    { 
     Log.d(context.getString(R.string.tag_receipttracker), e.getMessage()); 
     showToast(MESSAGE_COULD_NOT_OPEN); 
    } 

    return receiptList; 
} 

這樣你只需要在之前創建適配器和光標在main方法傳遞下去他們，將執行所有呼叫的其餘邏輯。 我注意到有一種方法只是返回一個對象而不是數組。在這種情況下，您可以傳遞一個內部唯一對象的數組。

希望它有幫助。

讓我知道你的印象/更新。