Question

我想从现有数据库中检索金额并将其显示在TextView中。

我已经创建了数据库。但是，当我尝试获取并显示金额时，我的应用会崩溃。

/ DataBaseHelper.java /

   public Cursor getBalance(String amount) {
    SQLiteDatabase db = this.getReadableDatabase();

    String selectQuery = "SELECT  * FROM " + TABLE_USER_BALANCE + " WHERE "
            + KEY_AMOUTNT + " = " + amount;

    Log.e(LOG, selectQuery);

    Cursor c = db.rawQuery(selectQuery, null);

    if (c != null)
        c.moveToFirst();

    Balance b = new Balance();
    b.setAmount(c.getInt(c.getColumnIndex(KEY_AMOUTNT)));

    return (Cursor) b;
}

仪表板类：

public void saveCallBack(Balance balance) {


   DataBaseHelper dataBaseHelper = new DataBaseHelper(context);
    Cursor cursor = dataBaseHelper.getBalance(DashBoard.email);
  while (cursor.moveToNext()) {
        String s_amount = "";
        s_amount = 
      cursor.getString(cursor.getColumnIndex(DataBaseHelper.KEY_AMOUTNT));

        Double amount = 0.0;
        if (AppUtility.isNum(s_amount)) {
            amount = Double.parseDouble(s_amount);
        }

        TextView Amount = findViewById(R.id.amount);
        Amount.setText(String.valueOf(amount));


    }

}

Answer 1

您无法将Balance投射到Cursor，因此您的应用程序将崩溃。您要么返回数据库Cursor本身，要么返回Balance对象。您已经制作了Balance实例并在其中放置了一些值，所以我认为您的代码应为：

public Balance getBalance(String amount) {
    ...

    Balance b = new Balance();
    b.setAmount(c.getInt(c.getColumnIndex(KEY_AMOUTNT)));
    return b;
}

我建议您学习有关Java转换的更多信息，以便您了解转换行为。

如何在textview中显示单个SQLite数据？

1 个答案: