Adicionando Atributos em Propriedades (C#)
Nem sempre é possível utilizar objetos complexos (classes) para incluir informações em propriedades de classes. Essa situação pode acontecer quando se está dando manutenção em um código que está amarrado a outro comportamento que não pode ser alterado.
No caso que deu origem à esse código, a classe possui uma dezena de propriedades públicas string que já estavam atreladas a outras classes e comportamento em outras partes do código. Não havia liberdade de criação de outras classes que incorporassem mais propriedades, então decidi enfeitar cada propriedade com atributos personalizados.
Dessa forma, foi possível no código acessar mais informações com base somente nessa propriedade string.
O código foi usado em uma aplicação de aluguel de móveis para eventos. Segue o código:
Classe do Objeto amarrado (Furniture.cs) com as classes de atributos no mesmo arquivo (para facilitar o entendimento)
using System;
using System.ComponentModel;
using System.Globalization;
using static ADX18.Library.Helpers.ADX18Helper;
namespace ADX18.Library.Models
{
public class Furniture : iTestObject
{
[DisplayName("Mode Cupboard"),
MemberPrice("225.50"),
NonMemberPrice("247.50")]
public string ModeCupboard_Quantity { get; set; }
public string ModeCupboard_Colour { get; set; }
[DisplayName("Poly Voge Chair"),
MemberPrice("52.25"),
NonMemberPrice("55.00")]
public string PolyVogue_Quantity { get; set; }
public string PolyVogue_Colour { get; set; }
[DisplayName("Poly Vogue Stool"),
MemberPrice("74.25"),
NonMemberPrice("80.85")]
public string PolyVogueStool_Quantity { get; set; }
public string PolyVogueStool_Colour { get; set; }
[DisplayName("Club Stool"),
MemberPrice("77.00"),
NonMemberPrice("82.50")]
public string ClubStool_Quantity { get; set; }
public string ClubStool_Colour { get; set; }
[DisplayName("Ikon Dry Bar"),
MemberPrice("165.00"),
NonMemberPrice("177.65")]
public string IkonDryBar_Quantity { get; set; }
public string IkonDryBar_Colour { get; set; }
[DisplayName("Ikon Meeting Table"),
MemberPrice("143.00"),
NonMemberPrice("154.00")]
public string IkonMeetingTable_Quantity { get; set; }
public string IkonMeetingTable_Colour { get; set; }
[DisplayName("Ikon Illuminated Dry Bar"),
MemberPrice("192.50"),
NonMemberPrice("209.00")]
public string IkonIlluminatedDryBar_Quantity { get; set; }
public string IkonIlluminatedDryBar_Colour { get; set; }
[DisplayName("Mode Dry Bar Table"),
MemberPrice("104.50"),
NonMemberPrice("108.90")]
public string ModeDryBarTable_Quantity { get; set; }
public string ModeDryBarTable_Colour { get; set; }
[DisplayName("Mode Meeting Table"),
MemberPrice("99.00"),
NonMemberPrice("107.25")]
public string ModeMeetingTable_Quantity { get; set; }
public string ModeMeetingTable_Colour { get; set; }
[DisplayName("Mode Coffee Table"),
MemberPrice("93.50"),
NonMemberPrice("100.65")]
public string ModeCoffeeTable_Quantity { get; set; }
public string ModeCoffeeTable_Colour { get; set; }
[DisplayName("Cuba Lounge One Seater"),
MemberPrice("165.00"),
NonMemberPrice("189.75")]
public string CubaLoungeOneSeater_Quantity { get; set; }
public string CubaLoungeOneSeater_Colour { get; set; }
[DisplayName("Cuba Lounge One Seater Corner"),
MemberPrice("165.00"),
NonMemberPrice("189.75")]
public string CubaLoungeOneSeaterCorner_Quantity { get; set; }
public string CubaLoungeOneSeaterCorner_Colour { get; set; }
[DisplayName("Cuba Lounge One Seater No Arm Rests"),
MemberPrice("165.00"),
NonMemberPrice("189.75")]
public string CubaLoungeOneSeaterNoArms_Quantity { get; set; }
public string CubaLoungeOneSeaterNoArms_Colour { get; set; }
[DisplayName("Cuba Lounge"),
MemberPrice("275.00"),
NonMemberPrice("308.00")]
public string CubaLounge_Quantity { get; set; }
public string CubaLounge_Colour { get; set; }
[DisplayName("Quattro Display Plinth 600mm"),
MemberPrice("165.00"),
NonMemberPrice("178.75")]
public string QuattroDisplay600_Quantity { get; set; }
public string QuattroDisplay600_Colour { get; set; }
[DisplayName("Quattro Display Plinth 900mm"),
MemberPrice("187.00"),
NonMemberPrice("207.90")]
public string QuattroDisplay900_Quantity { get; set; }
public string QuattroDisplay900_Colour { get; set; }
[DisplayName("Zig Zag Brochure Stand"),
MemberPrice("115.50"),
NonMemberPrice("123.20")]
public string ZigZagStand_Quantity { get; set; }
public string ZigZagStand_Colour { get; set; }
[DisplayName("Carpet Floor Tiles"),
MemberPrice("247.50"), NonMemberPrice("287.10"),
NonMemberUnitPrice("31.90"),
MemberUnitPrice("27.50")]
public string CarpetFloorTiles_Quantity { get; set; }
public string CarpetFloorTiles_Colour { get; set; }
[DisplayName("Raised Floor Tiles"),
MemberPrice("940.50"),
NonMemberPrice("1188.00"),
NonMemberUnitPrice("132.00"),
MemberUnitPrice("104.50")]
public string RaisedFloorTiles_Quantity { get; set; }
public string RaisedFloorTiles_Colour { get; set; }
}
// Classes de Atributos personalizadas
public class NonMemberUnitPrice : Attribute
{
private decimal value;
public decimal Value => value;
public NonMemberUnitPrice(string number)
{
value = decimal.Parse(number, CultureInfo.InvariantCulture);
}
}
public class NonMemberPrice : Attribute
{
private decimal value;
public decimal Value => value;
public NonMemberPrice(string number)
{
value = decimal.Parse(number, CultureInfo.InvariantCulture);
}
}
public class MemberUnitPrice : Attribute
{
private decimal value;
public decimal Value => value;
public MemberUnitPrice(string number)
{
value = decimal.Parse(number, CultureInfo.InvariantCulture);
}
}
public class MemberPrice : Attribute
{
private decimal value;
public decimal Value => value;
public MemberPrice(string number)
{
value = decimal.Parse(number, CultureInfo.InvariantCulture);
}
}
}
Código de acesso desses atributos listados como um Dictionary<string,object> pois os valores retornados em cada atributo podem variar:
using ADX18.Library.Models;
using System;
using System.Collections.Generic;
using System.Linq.Expressions;
namespace ADX18.Library.Helpers
{
public static class ADX18Helper
{
#region Furniture Helpers
public interface iField { }
public interface iTestObject { }
//tweaked from https://stackoverflow.com/questions/6637679/reflection-get-attribute-name-and-value-on-property
//and https://stackoverflow.com/questions/23329087/get-custom-attribute-from-specific-object-property-field
public static Dictionary<string, object> GetAttributes<T>(this T source, Expression<Func<object>> field) where T : class
{
MemberExpression member = (MemberExpression)field.Body;
if (member == null) { return null; }
Dictionary<string, object> _dict = new Dictionary<string, object>();
object[] propertyAttributes = typeof(T).GetProperty(member.Member.Name)
.GetCustomAttributes(true);
foreach (var propertyAttribute in propertyAttributes)
{
var attributeAttributes = propertyAttribute.GetType().GetProperties();
foreach (var attributeAttribute in attributeAttributes)
{
var propName = $"{propertyAttribute.GetType().Name}.{attributeAttribute.Name}";
if (!_dict.ContainsKey(propName) && attributeAttribute.Name != "TypeId")
_dict.Add(propName, attributeAttribute.GetValue(propertyAttribute, null));
}
}
return _dict;
}
#endregion
}
}
Com essas classes definidas, fica mais fácil acessar os atributos no Razor:
@model Furniture
@using ADX18.Library.Controllers
@using ADX18.Library.Models
@using ADX18.Library.Helpers;
<div class="col-md-8">
@{
var modeCupboard = Model.GetAttributes<Furniture>(() => Model.ModeCupboard_Quantity);
}
<h5>@modeCupboard["DisplayNameAttribute.DisplayName"]</h5>
<p>
Available in four colours, this includes a lockable cupboard with shelves.<br />
L: 1200mm x W: 600mm x H: 1000mm
</p>
<div>
Member: <span class="memberPrice">$@modeCupboard["MemberPrice.Value"] each</span><br />
Non-member: <span class="memberPrice">$@modeCupboard["NonMemberPrice.Value"] each</span>
</div>
Quantity: <input type="text" name="ModeCupboard_Quantity" style="width: 10%;" />
<select name="ModeCupboard_Colour">
<option value="White">White</option>
<option value="Black">Black</option>
<option value="Red">Red</option>
<option value="Blue">Blue</option>
</select>
</div>
Então, quando não puder mudar uma propriedade para incluir objetos complexos, use atributos personalizados!
