Question

我有以下代码从SQLite数据库中读取数据。我可以检测到空游标，但我不知道如何逃避它。我无法将return语句移到if( result != null && result.moveToFirst()语句中。我得到最后两个日志行，然后程序崩溃

/CSV Import﹕ cursor index is NOT greater than 0
/CSV Import﹕ Null Cursor Found

代码：

public Equipment getEquipmentByID(int id){
    SQLiteDatabase db = this.getReadableDatabase();

    String SQL = "SELECT "+EQUIPMENT_TABLE+".*, "+LOCATION_TABLE+"."+LOCATION_NAME+" as locationName FROM "+ EQUIPMENT_TABLE + " " +
            "JOIN "+LOCATION_TABLE + " ON "+LOCATION_TABLE+"."+LOCATION_ID+"="+EQUIPMENT_TABLE+"."+EQUIPMENT_LOCATION+" " +
                    "WHERE "+EQUIPMENT_TABLE+"."+EQUIPMENT_ID +"="+id;

    Cursor result = db.rawQuery(SQL, null);
    result.moveToFirst();

    if(result != null && result.moveToFirst()) {
        Log.v("CSV Import", "Null Cursor not Found");
    } else {
        if (result.getCount()>0) {
            Log.v("CSV Import", "cursor index is grater than 0");
        } else {
            Log.v("CSV Import", "cursor index is NOT greater than 0");
        }
        Log.v("CSV Import", "Null Cursor Found");
    }

    Equipment equipment = new Equipment(result.getInt(result.getColumnIndex(EQUIPMENT_ID)), result.getString(result.getColumnIndex(EQUIPMENT_NAME)),
            result.getString(result.getColumnIndex(EQUIPMENT_MODEL)), result.getString(result.getColumnIndex(EQUIPMENT_SERIAL)),
            result.getString(result.getColumnIndex(EQUIPMENT_NOTES)), new Location(result.getInt(result.getColumnIndex(EQUIPMENT_LOCATION)),
            result.getString(result.getColumnIndex("locationName"))), new EquipmentType(1, "Undefined"));
    return equipment;
}

Answer 1

From the docs，如果光标为空，moveToFirst()将返回false，否则为true。所以从第一行开始：result.moveToFirst();将所有内容替换为：

if(result == null) return null;

if(!result.moveToFirst()) {
    result.close();
    db.close();
    return null; 
}

Equipment equipment = new Equipment(result.get //.... and so on ....//);
result.close();
db.close();
return equipment;

Answer 2

结果永远不为空，你的代码错了，这对你很好

public Equipment getEquipmentByID(int id)
{
    SQLiteDatabase db = this.getReadableDatabase();

    String SQL = "SELECT "+EQUIPMENT_TABLE+".*, "+LOCATION_TABLE+"."+LOCATION_NAME+" as locationName FROM "+ EQUIPMENT_TABLE + " " +
            "JOIN "+LOCATION_TABLE + " ON "+LOCATION_TABLE+"."+LOCATION_ID+"="+EQUIPMENT_TABLE+"."+EQUIPMENT_LOCATION+" " +
                    "WHERE "+EQUIPMENT_TABLE+"."+EQUIPMENT_ID +"="+id;

            Cursor result = db.rawQuery(SQL, null);
            //result.moveToFirst();
    if(result.moveToFirst()) {
        //Log.v("CSV Import", "Null Cursor not Found");
    Equipment equipment = new Equipment(result.getInt(result.getColumnIndex(EQUIPMENT_ID)), result.getString(result.getColumnIndex(EQUIPMENT_NAME)),
            result.getString(result.getColumnIndex(EQUIPMENT_MODEL)), result.getString(result.getColumnIndex(EQUIPMENT_SERIAL)),
            result.getString(result.getColumnIndex(EQUIPMENT_NOTES)), new Location(result.getInt(result.getColumnIndex(EQUIPMENT_LOCATION)),
            result.getString(result.getColumnIndex("locationName"))), new EquipmentType(1, "Undefined"));


    return equipment;

}

        else
            {
Log.v("CSV Import", "cursor index is NOT greater than 0");
            //if (result.getCount()>0)
           // {Log.v("CSV Import", "cursor index is grater than 0");}
            //else
            //{Log.v("CSV Import", "cursor index is NOT greater than 0");}
            //Log.v("CSV Import", "Null Cursor Found");

        }
    result.close;

}

找到null游标时如何返回

2 个答案: