Enum, tapi String
Ikhwan Hayat
Dalam C#, biasanya, utk value yg hanya boleh dipilih dari satu set of
values, kita pakai `enum`. E.g:
class Student
{
public StudentStatus Status { get; set; }
}
enum StudentStatus
{
Active,
Suspended,
Dismissed
}
Tapi, kalau value tu *bukan* int, mungkin memerlukan string supaya
data lebih mudah dibaca, mcm mana nak buat? Contohnya,
class Student
{
public string Status { get; set; }
}
Value utk Student.Status mestilah sama ada "A", "S", atau "D" utk
Active, Suspended, atau Dismissed.
Macam mana cara nak buat supaya dua kekangan dibawah masih dihormati:
1) Value yg boleh di set *mesti* salah satu dari nilai yang dibenarkan
(Active, Suspended atau Dismissed).
2) Value yang disimpan *mesti* nilai yang sebenar yang tersebut (A, S,
atau D).
Macam mana korang selalu buat?
Rushdan Mamat
enum StudentStatus
{
Active = "A",
Suspended = "S",
Dismissed ="D"
}
ron
ron
{
/// <summary/>
Active = "A",
/// <summary/>
Suspended = "S",
/// <summary/>
Dismissed ="D"
}
Ikhwan Hayat
> public enum StudentStatus : String
> {
> /// <summary/>
> Active = "A",
> /// <summary/>
> Suspended = "S",
> /// <summary/>
> Dismissed ="D"
> }
>
Betul ke korang ni...
Dari MSDN <msdn.microsoft.com/en-us/library/sbbt4032(VS.80).aspx>
"Every enumeration type has an underlying type, which can be any
integral type except char"
Aku try run code ron ni, dapat compile error:
"Type byte, sbyte, short, ushort, int, uint, long, or ulong expected"
ron
ron
Ikhwan Hayat
> hehe aku wat pakai logik je, tak test pon, dah lama tak sentuh enum
Hoho.. tak pakai enum? Living live dangerously free and wild :D
Actually, ni yg aku selalu buat:
class Student
{
///<summary>Value must be from Student.Statuses</summary>
public string Status { get; set; }
public class Statuses
{
public const string Active = "A";
public const string Suspended = "S";
public const string Dismissed = "D";
}
}
var s = new Student();
s.Status = Student.Statuses.Active;
Melalui cara ni, kita boleh dapat intellisense support utk values yg
*mungkin* bagi Status.
Tapi tak boleh enforce compile time check kalau dia bagi string lain. E.g:
Tak produce error bila s.Status = "X";
Dan tak comply pun dgn dua-dua kekangan tadi.
Ikhwan Hayat
> Ni ada good way http://blog.waynehartman.com/articles/84.aspx
Memang pernah nampak solution mcm ni sebelum ni.. Tapi tak comply
kekangan yg kedua:
2) Value yang disimpan *mesti* nilai yang sebenar yang tersebut (A, S,
atau D).
Sebabnya, kadang2 penting utk simpan value yg *bermakna* dalam
database. Dlm contoh ni, sekali imbas dah tau Student tu (A)active,
(S)suspended, atau (D)ismissed. Kalau kita simpan enum, atau
underlying typenya yg biasanya int, kita kena tahu 0 adalah active, 1
adalah suspended, 2 adalah dismissed. Leceh beb.
Baru terfikir, boleh ke buat something yg mcm ni, guna Attribute maybe?
[AllowedValues("A", "S", D")]
string Status { get; set; }
Macam design by contract?
ron
enum StudentStatus : byte
{
[Description("A")]
Active,
[Description("S")]
Suspended,
[Description("D")]
Dismissed
}
class Description : Attribute
{
public string Text;
public Description(string text)
{
Text = text;
}
}
class Program
{
static string GetDescription(Enum en)
{
Type type = en.GetType();
MemberInfo[] memInfo = type.GetMember(en.ToString());
if (memInfo != null && memInfo.Length > 0)
{
object[] attrs = memInfo[0].GetCustomAttributes(typeof(Description),
false);
if (attrs != null && attrs.Length > 0)
return ((Description)attrs[0]).Text;
}
return en.ToString();
}
static void Main(string[] args)
{
StudentStatus status1 = StudentStatus.Active;
StudentStatus status2 = StudentStatus.Suspended;
StudentStatus status3 = StudentStatus.Dismissed;
Console.WriteLine(GetDescription(status1));
Console.WriteLine(GetDescription(status2));
Console.WriteLine(GetDescription(status3));
}
}
Ikhwan Hayat
Any simple and elegant solution? Ok, at least maybe some extra code
upfront utk utility class/attributes is allowed, tapi kalau boleh masa
nak guna tu simple je.
Mungkin tak perlu pakai enum pun, tapi 2 syarat tadi tu kena ikut.
Ikhwan Hayat
On Feb 24, 10:15 am, Ikhwan Hayat <ikhwanha...@gmail.com> wrote:
> [AllowedValues("A", "S", D")]
> string Status { get; set; }
>
> Macam design by contract?
class Student
{
string Status { get; set; }
}
(atau mungkin method parameters), yang mana in compile time, compiler
akan check apa value yg di set ke Status tu sama ada allowed ke tak.
Tapi nak buat attribute mcm ni susah. Ini dah masuk mcm Aspect
Oriented Programming la plak. Lagi la payah :P
Kena la tunggu C# ada feature utk enum with underlaying type string.