Adding on to the current value SQLite

问题

I have a user who has a starting value for their credits set at '5'. Now I want to create a method which will allow the user to add on to that number, e.g. 2. This will then update the row in the database column to become 7.

However I cant get my current method to do this.

Current method:

    public void upDateUser(String money) 
    {
        String selectQuery = "SELECT " + KEY_CREDITS + " from " + 
                                 DATABASE_TABLE + " where " + KEY_ROWID + " = " + 0;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor c = db.rawQuery(selectQuery, null);
        int oldMoney = 0;
        if (c.moveToFirst()) 
        {         
            oldMoney = Integer.parseInt(c.getString(4));
        }
        ContentValues cvUpdate = new ContentValues();
        cvUpdate.put(KEY_CREDITS, (oldMoney + money));
        String filter = KEY_ROWID + "=" + 0;
        db.update(DATABASE_TABLE, cvUpdate, filter, null);
    }

I then call the above method in an another activity:

public void onClick(View arg0)
{
    switch (arg0.getId()){
    case R.id.topup:

        boolean work = true;
        try{
        String money = spinner.getSelectedItem().toString();

        UDbHelper ud = new UDbHelper(this);
        ud.open();
        ud.upDateUser(money);
        ud.close();

回答1:

Change the following step to get the value of oldmoney

oldMoney = c.getInt(c.getColumnIndex(KEY_CREDITS));

Also you cannot add strings to get an integer total value. So convert the value money to integer before finding the total

int money =Integer.parseInt(money);

If you have a string data type for KEY_CREDITS column then after finding the total you should convert it back to string before updating

cvUpdate.put(KEY_CREDITS, String.valueOf(oldMoney + money));

来源：https://stackoverflow.com/questions/23047462/adding-on-to-the-current-value-sqlite