有人说枚举类型违反了Clean Code原则，因此我正在寻找人们最喜欢的枚举反模式以及这些反模式的替代方案。
例如，我见过以下代码：
switch(enumValue) {
case myEnum.Value1:
// ...
break;
case myEnum.Value2:
// ...
break;
}
这种方法比使用魔法字符串的switch语句更好一步，但可能可以通过工厂、容器或其他模式更好地解决问题。
甚至可以像这样使用老式代码：
if(enumValue == myEnum.Value1) {
// ...
} else if (enumValue == myEnum.Value2) {
// ...
}
我认为枚举非常有用。我写了一些扩展方法来增强它的价值。
首先，有一个Description扩展方法。
public static class EnumExtensions
{
public static string Description(this Enum value)
{
var entries = value.ToString().Split(ENUM_SEPERATOR_CHARACTER);
var description = new string[entries.Length];
for (var i = 0; i < entries.Length; i++)
{
var fieldInfo = value.GetType().GetField(entries[i].Trim());
var attributes = (DescriptionAttribute[])fieldInfo.GetCustomAttributes(typeof(DescriptionAttribute), false);
description[i] = (attributes.Length > 0) ? attributes[0].Description : entries[i].Trim();
}
return String.Join(", ", description);
}
private const char ENUM_SEPERATOR_CHARACTER = ',';
}
这将使我能够像这样定义一个枚举：
public enum MeasurementUnitType
{
[Description("px")]
Pixels = 0,
[Description("em")]
Em = 1,
[Description("%")]
Percent = 2,
[Description("pt")]
Points = 3
}
通过执行以下代码可以获取标签：var myLabel = rectangle.widthunit.Description()（无需使用switch语句）。
如果rectangle.widthunit = MeasurementUnitType.Pixels，则会返回"px"；如果rectangle.widthunit = MeasurementUnitType.Pixels | MeasurementUnitType.Em，则会返回"px,em"。
然后，这里有一个
public static IEnumerable<int> GetIntBasedEnumMembers(Type @enum)
{
foreach (FieldInfo fi in @enum.GetFields(BindingFlags.Public | BindingFlags.Static))
yield return (int)fi.GetRawConstantValue();
}
哪种方法可以让我遍历任何具有基于int值的枚举并返回int值本身。
我认为这些在已经有用的概念中非常有用。
这完全取决于您对枚举类型的使用目的。
If you are trying to stop your developers from passing magic numbers into your operations and you want to keep the data referential integrity intact with your DB then, YES! Use T4-Templates (using your ORM) to go to your MeasurementUnitTypes table and generate a enum with the ID, Name and Description columns matching the enum’ int, Enum_Name and Description Attribute (nice approach for additional field\data to enum @danijels) as suggested above. If you add a new Measurement Type to your MeasurementUnitTypes table you can just right click and run the T4-Template and the enum code is generated for that new row added in the table. I don’t like hard-coded data in my application that doesnt link to my DB hence the mention of the T4-Template approach. It is not extensible otherwise...what if some other external system wants to retrieve our Measurement Criteria used in our system, then it is hard-coded in the system and you can't expose it to the client via a service. That left there.
If the purpose is not data related and you have some logic assigned to a specific enum then NO! this violates the SOLID (Open close principle) as you would somewhere in your application apply a switch or bunch of Ifs to action the logic per enum, ALSO if you did it REALLY bad these switches or Ifs are all over the show....good luck adding a new enum... so it is not open for extension and closed for modification as you need to modify existing code, as per the SOLID principle.
If your choice is 2 then I suggest then to replace your enum with the following using the example from @danijels comment:
public interface IMeasurementUnitType
{
int ID { get; }
string Description { get; }
// Just added to simulate a action needed in the system
string GetPrintMessage(int size);
}
public class PixelsMeasurementUnitType : IMeasurementUnitType
{
public int ID => 1;
public string Description => "Pixel";
public string GetPrintMessage(int size)
{
return $"This is a {Description} Measurement that is equal to {size} pixels of the total screen size";
}
}
public class PercentMeasurementUnitType : IMeasurementUnitType
{
public int ID => 2;
public string Description => "Persentage";
public string GetPrintMessage(int size)
{
return $"This is a {Description} Measurement that is equal to {size} persent of total screen size (100)";
}
}
我们定义了两个类型，我们会在代码中使用它们，如下所示：
var listOfMeasurmentTypes = AppDomain.CurrentDomain.GetAssemblies()
.SelectMany(s => s.GetTypes())
.Where(p => typeof(IMeasurementUnitType).IsAssignableFrom(p)
&& !p.IsInterface)
.ToList();
public IEnumerable<IMeasurementUnitType> GetInstantiatedClassesFromTypes(List<Type> types)
{
foreach (var type in types)
{
yield return (IMeasurementUnitType)Activator.CreateInstance(type);
}
}
您可以将上面的代码更改为通用类型，现在情况发生了变化，客户提出了一个名为“Point”的新测量单位类型作为新需求，我不需要更改任何代码，只需添加新类型（扩展代码而非修改）。新类型将自动在应用程序中被识别。
public class PointMeasurementUnitType : IMeasurementUnitType
{
public int ID => 3;
public string Description => "Point";
public string GetPrintMessage(int size)
{
return $"This is a {Description} Measurement that is equal to {size} points of total screen size";
}
}
..
public enum ListEnum
{
CategoryOne,
CategoryTwo,
CategoryThree,
CategoryFour
}
public class UIELementType
{
public const string FactoryDomain = "FactoryDomain";
public const string Attributes = "Attributes";
}
在编程中使用枚举并不是反模式。在一些关于重构的书籍中，这段代码被用来演示如何用多态性来替换它。当你在代码中过度使用枚举时，这种做法就没问题了。
switch与枚举本身并不是不好的。有时它是必要的，比如在提到的工厂中。 - AndreyDictionary<myEnum,Action<> >->actionDictionary[enumValue]();- Pasi Savolainen