C#：有没有办法对枚举进行分类？

Question

给定以下枚举：

    public enum Position
    {
        Quarterback,
        Runningback,
        DefensiveEnd,
        Linebacker
    };

是否可以对命名常量进行分类，以便我可以将“Quarterback”和“Runningback”标记为进攻位置，将“DefensiveEnd”和“Linebacker”标记为防守位置？

Answer 1

你可以使用属性：

public enum Position
{
    [OffensivePosition]
    Quarterback,
    [OffensivePosition]
    Runningback,
    [DefensivePosition]
    DefensiveEnd,
    [DefensivePosition]
    Linebacker
};

然后在适当的FieldInfo 上检查IsDefined。语法不是很漂亮，但是您可以添加一些扩展方法来使事情更易于管理：

public static bool IsOffensivePosition(PositionType pt)
{
    return typeof(PositionType).GetField(Enum.GetName(typeof(PositionType), pt)).
        IsDefined(typeof(OffensivePositionAttribute), false);
}

Answer 2

你可以使用一个属性，比如CategoryAttribute：

public enum Position
{
    [Category("Offensive")]
    Quarterback,
    [Category("Offensive")]
    Runningback,
    [Category("Defensive")]
    DefensiveEnd,
    [Category("Defensive")]
    Linebacker
};

Answer 3

为什么不接吻：

class PlayerPosition {
    public enum Position {
        Quarterback,
        Runningback,
        DefensiveEnd,
        Linebacker
    }

    public enum Type {
        Offense,
        Defense
    }


    public static Type GetTypeForPosition(Position position) {
        switch (position) {
            case Quarterback:
            case Runningback:
                return Type.Offense;
            case DefensiveEnd:
            case Linebacker:
                return Type.Defense;

        }
    }
}

Answer 4

public enum PositionType
{
    Offensive,
    Defensive,
}

public class PositionTypeAttribute : Attribute
{
    public PositionTypeAttribute(PositionType positionType)
    {
        PositionType = positionType;
    }
    public PositionType PositionType { get; private set; }
}

public enum Position
{
    [PositionType(PositionType.Offensive)]
    Quarterback,
    [PositionType(PositionType.Offensive)]
    Runningback,
    [PositionType(PositionType.Defensive)]
    DefensiveEnd,
    [PositionType(PositionType.Defensive)]
    Linebacker
};

public static class PositionHelper
{
    public static PositionType GetPositionType(this Position position)
    {
        var positionTypeAttr = (PositionTypeAttribute)typeof(Position).GetField(Enum.GetName(typeof(Position), position))
            .GetCustomAttributes(typeof(PositionTypeAttribute), false)[0];
        return positionTypeAttr.PositionType;

    }
}


Position position1 = Position.Runningback;
Console.WriteLine(position1.GetPositionType()); //print: Offensive

Position position2 = Position.Linebacker;
Console.WriteLine(position2.GetPositionType()); //print: Defensive

Answer 5

你可以使用Flags

[Flags]
public enum Position
    {
        Quarterback = 1,
        Runningback = 2,
        DefensiveEnd = 4,
        Linebacker = 8,

        OffensivePosition = Quarterback | Runningback,
        DefensivePosition =  Linebacker | DefensiveEnd, 

    };

    //strictly for example purposes
    public bool isOffensive(Position pos)
    {
        return !((pos & OffensivePosition) == pos);
    }

Answer 6

也许你可以尝试使用typesefe enum pattern

class Position
{
    public bool Offensive { get; private set; }
    public bool Defensive { get; private set; }

    private Position()
    {
        Offensive = false;
        Defensive = false;
    }

    public static readonly Position Quarterback = new Position() { Offensive = true };
    public static readonly Position Runningback = new Position() { Offensive = true };
    public static readonly Position DefensiveEnd = new Position() { Defensive = true };
    public static readonly Position Linebacker = new Position() { Defensive = true };
}

Answer 7

您可以使用某种形式的标志位。但这可能会导致混乱。更好的方法可能是只使用您想要的详细信息创建自定义类，然后使用字典来查找每种职位类型；

public class PlayerPosition {
    public PlayerPosition (string positionName, bool isDefensive ) {
        this.Name = positionName;
        this.IsDefensive = isDefensive ;
    }
    public string Name { get; private set; }
    public bool IsDefensive { get; private set; }
}

...作为枚举...

[Flags]
public enum Positions {
    Quarterback = 0x21, 
    Runningback = 0x22, 
    DefensiveEnd = 0x14, 
    Linebacker = 0x18, 

    Defensive = 0x10,
    Offsensive = 0x20
}

Answer 8

一种未充分利用（但完全有效）的技术是使用定义一组常量的类。作为一个类，您可以添加其他属性来描述枚举值的其他方面。奇怪的是，这是大多数枚举在 Java 中实现的方式（没有特殊的关键字）。

如果你走这条路，通常最好将类密封并定义一个私有构造函数，这样只有类本身才能定义实例。这是一个例子：

public static class Position 
{
    private PlayerPosition (string name, bool isDefensive ) {
        this.Name = name
        this.IsDefensive = isDefensive ;
    }
    // any properties you may need...
    public string Name { get; private set; }
    public bool IsDefensive { get; private set; }
    public bool IsOffensive { get { return !IsDefensive; } }

    // static instances that act like an enum
    public static readonly Quarterback = new PlayerPosition( "Quarterback", false );
    public static readonly Runningback = new PlayerPosition( "Runningback", false );
    public static readonly Linebacker = new PlayerPosition( "Linebacker", true );
    // etc...
}

使用这样的枚举会产生比属性更优雅、更简单的语法：

if( PlayerPosition.Quarterback.IsDefensive )
{
    // ...
}

Answer 9

你可以在一个类中声明枚举：

public class Position
{
    public enum Offensive { Quarterback = 1, RunningBack }
    public enum Defensive { DefensiveEnd = 10, LineBacker }
}

请注意，防御值从 10 开始，因此值不会重叠。您没有说明为什么要这样做，因此这可能无法满足您的需求。