有没有到奇怪的循环模板模式的方法吗？ [英] Is there an alternative to the Curiously Recurring Template Pattern?

问题描述

我自己造成了与好奇地重复模板 。模式

I've caused myself some headaches over the past couple of weeks with the curiously recurring template pattern.

这是我的这两个问题继：

Following on from these two questions of mine:

• 什么是获取$ b的正确方法$ b由$ b $我的自定义枚举b类自己的价值？


• 的为什么不是我的静态物体时的
  第一次访问静态类是
  实例在
  基类的静态方法

• What’s the correct way of retrieving my custom enumeration classes by their value?
• Why are my static objects not being instantiated when first access to the static class is a static method on the base class?

如何改进下面的例子：

public class DocketType : Enumeration<DocketType, int, string>
{
    public static DocketType Withdrawal = new DocketType(2, "Withdrawal");
    public static DocketType Installation = new DocketType(3, "Installation");

    private DocketType(int docketTypeId, string description) 
        : base(docketTypeId, description) { }
}

我想，我没有在枚举类重复一个静态方法：

I want a static method that I don't have to repeat in the Enumeration class:

public abstract class Enumeration<TEnum, X, Y> : IComparable 
    where TEnum : Enumeration<TEnum, X, Y> 
{        
    protected Enumeration(X value, Y displayName)
    {
        AddToStaticCache(this);
    }
    public static TEnum Resolve(X value)
    {
        return Cache[value] as TEnum;
    }
}

这个问题，因为你会看到从我的第二个链接的问题，就是调用枚举< DocketType，整型，字符串> .Resolve（X值）; 不会引起 DocketType <被实例化/ code>静态对象。

The problem with this, as you'll see from my second linked question, is that the call to Enumeration<DocketType, int, string>.Resolve(X value); does not cause the DocketType static objects to be instantiated.

我并不反对完全从头开始重写此。我知道这是一个很大的代码味道。目前，得到这个工作我的基类有受保护的静态方法 ChildResolve 和我添加解析到每个我的枚举类。 ！讨厌的东西。

I'm not adverse to totally rewriting this from scratch. I'm aware it's a big code smell. Currently, to get this working my base class has the protected static method ChildResolve and I've added Resolve to each of my Enumeration classes. Nasty stuff!

答：

似乎没有很好的替代模式，所以我坚持用模式，把灵感来自公认的答案以及与此想出了：

Seems there was no nice alternative to the pattern, so I stuck with the pattern and took inspiration from the accepted answer and came up with this:

static Enumeration()
{
    GetAll();
}

public static void GetAll()
{
    var type = typeof(TEnum);
    var fields = type.GetFields(BindingFlags.Public | 
        BindingFlags.Static | BindingFlags.DeclaredOnly);

    foreach (var info in fields)
    {
        var locatedValue = info.GetValue(null) as Enumeration<TEnum, X, Y>;
        Cache.Add(locatedValue.Value, locatedValue);
    }
}

这也是用在CodeCampServer MVC相同的代码示例项目，所以我觉得不太脏的使用它！

This is also the same code using in the CodeCampServer MVC example project, so I feel less dirty for using it!

推荐答案

这不是很优雅，但这样的事情可能会做的伎俩

It's not very elegant, but something like this might do the trick:

public class DocketType : Enumeration<DocketType, int, string>
{
    public static readonly DocketType Withdrawal =
        new DocketType(2, "Withdrawal");

    public static readonly DocketType Installation =
        new DocketType(3, "Installation");

    private DocketType(int docketTypeId, string description)
        : base(docketTypeId, description) { }
}

public abstract class Enumeration<TEnum, TId, TDescription> : IComparable
    where TEnum : Enumeration<TEnum, TId, TDescription>
{
    private static readonly Dictionary<TId, TEnum> _cache;

    static Enumeration()
    {
        Type t = typeof(TEnum);
        _cache = t.GetFields(BindingFlags.Public | BindingFlags.Static)
                  .Where(f => f.FieldType == t)
                  .Select(f => (TEnum)f.GetValue(null))
                  .ToDictionary(e => e.Id, e => e);
    }

    public static TEnum Resolve(TId id)
    {
        return _cache[id];
    }

    public TId Id { get; private set; }
    public TDescription Description { get; private set; }

    protected Enumeration(TId id, TDescription description)
    {
        Id = id;
        Description = description;
    }

    // IComparable
    public int CompareTo(object obj)
    {
        // TODO
        throw new NotImplementedException();
    }
}

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