Question

最初，我希望对枚举进行某种封装，但显然不是yet possible with C#。我的目的是用枚举存储某种数据。理想情况下，拥有一个对象的枚举会很棒。但显然没有办法做到这一点。所以我创建了一个状态类，一个公共枚举，并使用一个setter创建了一个公共getter / setter，该setter初始化一个方法，在该方法中我可以将对象填充为属性。我想知道是否有更好的方法。对我来说，理想的解决方案是以正常方式设置状态（枚举）：

car.State = CarStates.Idle;

然后访问有关该状态的更多数据，如下所示：

string message = car.State.Message();

但是这会涉及将属性附加到State枚举。有没有很酷的技巧来达到这个效果？枚举是唯一可以通过简单地将.Idle添加到结尾来制作可切换，类似单身的值的方法吗？

这是我现在拥有的代码，通过添加一个可通过的图层将状态信息保持在一个级别，但在声明car.Mode.State = CarModeStates.Idle;之类的内容时感觉多余。

class Car
{
    public CarState Mode;

    public Car()
    {
        Mode = new CarState();
    }
}

class CarState //holds any metadata for given enum value
{
    private int _EnumInt;
    private string _Message;
    private bool _IsError = false;

    public CarModeStates State
    { 
        get { return (CarModeStates)_EnumInt; } 
        set { _EnumInt = (int)value; InitializeState(value); } 
    }
    public string Message { get { return _Message; } }
    public bool IsError { get { return _IsError; } }

    public void InitializeState(CarModeStates? cs)
    {
        switch (cs)
        {
            case (CarModeStates.Off):
                {
                    _Message = "Car is off.";
                    _IsError = false;
                    break;
                }
            case (CarModeStates.Idle):
                {
                    _Message = "Car is idling.";
                    _IsError = false;
                    break;
                }
            case (CarModeStates.Drive):
                {
                    _Message = "Car is driving.";
                    _IsError = false;
                    break;
                }
            case (CarModeStates.Accident):
                {
                    _Message = "CRASH!";
                    _IsError = true;
                    break;
                }
        }
    }
}

public enum CarModeStates
{
    Off,
    Idle,
    Drive,
    Accident,
}

//And from the outside:
class SomeController
{
    Car car = new Car();
    public string GetStateMessage()
    {
        car.Mode.State = CarModeStates.Idle;

        return car.Mode.Message;
    }
}

Answer 1

您是否尝试过扩展方法？在静态类中，定义：

public static string Message( this CarStates value )
{
    switch (value) {
    ...
    }
}

Answer 2

C＃中的常规枚举通常不像您的问题所暗示的那样有问题。只需确保您的switch语句中有default个案例，该ArgumentException案例会引发0以确保您获得其中一个有效值。您必须小心使用文字值enum（可以隐式转换为任何枚举类型），但除此之外，C＃中的switch确实在API级别提供了实质性的类型安全性。

C＃enums比Java使用的完全封装的枚举更好地执行。还有一些需要注意的其他细节（例如超出范围的值），但它们在实践中很少引起问题。

Java风格的枚举类很容易在C＃中创建。 编辑：除了您不能在这样的枚举的C＃版本上使用sealed语句之外。

上课private。
确保该类至少有一个显式构造函数，并确保所有构造函数都是enum Color { RED, GREEN, BLUE }。
翻译以下成员：

爪哇：

private class Color {
    public static readonly Color RED = new Color();
    public static readonly Color GREEN = new Color();
    public static readonly Color BLUE = new Color();

    private Color() { }
}

C＃：

Enum<T>

如果您真的想模仿Java，可以通过为此表单的枚举创建Ordinal抽象基类来保持Values属性，并创建静态{{1}如Color类中的以下属性：

public Color[] Values { get { return new[] { RED, GREEN, BLUE }; } }

Answer 3

如果您想只使用Enum值，那么您可以创建自己的属性以提供额外的元数据。

以下示例适用于，但我个人不会以这种方式对我的域进行建模。

// sample test app
class Program
{
    static void Main(string[] args)
    {
        var carState = CarModeStates.Accident;

        // the call to get the meta data could and probably should be stored in a local variable
        Console.WriteLine(carState.GetMetaData().Message);
        Console.WriteLine(carState.GetMetaData().IsError);
        Console.WriteLine(carState.GetMetaData().IsUsingPetrol);
        Console.Read();
    }
}

扩展枚举示例

// enum with meta data
public enum CarModeStates
{
    [CarStatus("Car is off."), IsError(false), IsUsingPetrol(false)]
    Off,

    [CarStatus("Car is idling."), IsError(false), IsUsingPetrol(true)]
    Idle,

    [CarStatus("Car is driving."), IsError(false), IsUsingPetrol(true)]
    Drive,

    [CarStatus("CRASH!"), IsError(true), IsUsingPetrol(false)]
    Accident
}

用于装饰枚举的自定义属性

public interface IAttribute<out T>
{
    T Description { get; }
}

[AttributeUsage(AttributeTargets.Field)]
public class CarStatusAttribute : Attribute, IAttribute<string>
{
    private readonly string _value;

    public CarStatusAttribute(string value)
    {
        _value = value;
    }

    public string Description
    {
        get { return _value; }
    }
}

[AttributeUsage(AttributeTargets.Field)]
public class IsErrorAttribute : Attribute, IAttribute<bool>
{
    private readonly bool _value;

    public IsErrorAttribute(bool value)
    {
        _value = value;
    }

    public bool Description
    {
        get { return _value; }
    }
}

[AttributeUsage(AttributeTargets.Field)]
public class IsUsingPetrolAttribute : Attribute, IAttribute<bool>
{
    private readonly bool _value;

    public IsUsingPetrolAttribute(bool value)
    {
        _value = value;
    }

    public bool Description
    {
        get { return _value; }
    }
}

获取有关枚举的元数据的扩展方法。

public static class CarModeStatesExtensions
{
    public static CarModeStateModel GetMetaData(this CarModeStates value)
    {
        var model = new CarModeStateModel
            {
                Message = value.GetDescriptionFromEnumValue<string>(typeof (CarStatusAttribute)),
                IsError = value.GetDescriptionFromEnumValue<bool>(typeof(IsErrorAttribute)),
                IsUsingPetrol = value.GetDescriptionFromEnumValue<bool>(typeof (IsUsingPetrolAttribute))
            };

        return model;
    }
}

public class CarModeStateModel
{
    public string Message { get; set; }
    public bool IsError { get; set; }
    public bool IsUsingPetrol { get; set; }
}

public static class EnumExtensions
{
    public static T GetDescriptionFromEnumValue<T>(this CarModeStates value, Type attributeType)
    {
        var attribute = value.GetType()
            .GetField(value.ToString())
            .GetCustomAttributes(attributeType, false).SingleOrDefault();

        if (attribute == null)
        {
            return default(T);
        }

        return ((IAttribute<T>)attribute).Description;
    }
}

Answer 4

也许你需要一个像这样的“工厂”：

public class CarState
{
    private string message;
    private bool error;

    public CarState(string message, bool error)
    {
        this.message = message;
        this.error = error;
    }

    public string Message
    {
        get { return this.message; }
    }

    public bool Error
    { 
        get { return this.error; }
    }
}

public static class CarStateFactory
{
    public enum CarStateId { Off, Idle, Driving, Accident }

    public static CarState GetCarState(CarStateId carStateId)
    {
        switch(carStateId)
        {
            case (CarStateId.Off):
                { return new CarState("Car is off", false); }

            //add more cases

            default:
                return null;
        }
    }
}

通过这个，您可以通过以下方式设置您的汽车状态：

car.State = CarStateFactory.GetCarState(CarStateFactory.ID.Off); //ID.Idle, ID.Driving, ID.Accident

和

您可以使用car.State.Message。
访问该邮件
编辑： CarStateFactory的静态getter

public static CarState Idle { get { return new CarState("Car is off", false); } }

Answer 5

与字典结合使用的扩展方法可能是解决方案而不是switch语句。

public static class CarExtensionMethods
{
    public static string Message(this CarStates value)
    {
        return carStateDictionary[value];
    }

    private static readonly Dictionary<CarStates, string> carStateDictionary;

    static CarExtensionMethods()
    {
        carStateDictionary = new Dictionary<CarStates, string>();

        carStateDictionary.Add(CarStates.Off, "Car is off.");
        carStateDictionary.Add(CarStates.Idle, "Car is idling.");
        carStateDictionary.Add(CarStates.Drive, "Car is driving.");
        carStateDictionary.Add(CarStates.Accident, "CRASH!");
    }
}

用法很简单：

CarStates state = CarState.Idle;
Console.WriteLine(state.Message());  //writes "Car is idling."

另外，作为旁注，通常enum名称在具有[Flags]属性时应该只有复数。关键是要表明他们可以拥有多个州。枚举的更具风格的名称是CarState，因为它不能只有一个状态。

Answer 6

我知道这已经很老了但是对于更多的访问者来说，可能会使用一个状态管理器，而不是使用枚举来表示每个状态？

摘要

/// <summary>
/// Defines the expected members of a state
/// </summary>
internal interface ICarState
{
    /// <summary>
    /// Gets or sets the message.
    /// </summary>
    /// <value>
    /// The message.
    /// </value>
    string Message { get; }
}

基础状态

/// <summary>
/// The class that all car states should inherit from.
/// </summary>
internal abstract class CarBaseState : ICarState
{
    #region ICarState Members

    /// <summary>
    /// Gets or sets the message.
    /// </summary>
    /// <value>
    /// The message.
    /// </value>
    /// </exception>
    public abstract string Message { get; }

    #endregion
}

实施

/// <summary>
/// Represents the state when the car is off
/// </summary>
internal class OffState : CarBaseState
{
    /// <summary>
    /// Gets or sets the message.
    /// </summary>
    /// <value>
    /// The message.
    /// </value>
    /// </exception>
    public override string Message { get { return "Off"; } }
}

/// <summary>
/// Represents the state when the car is idling
/// </summary>
internal class IdleState : CarBaseState
{
    /// <summary>
    /// Gets or sets the message.
    /// </summary>
    /// <value>
    /// The message.
    /// </value>
    /// </exception>
    public override string Message { get { return "Idling"; } }
}

管理器

internal class CarStateManager
{
    #region Fields

    Dictionary<string, ICarState> _stateStore = null;

    #endregion

    #region Properties

    /// <summary>
    /// Gets (or privately sets) the state of the current.
    /// </summary>
    /// <value>
    /// The state of the current.
    /// </value>
    internal ICarState CurrentState { get; private set;  }

    #endregion

    #region Constructors and Initialisation

    /// <summary>
    /// Initializes a new instance of the <see cref="StateManager"/> class.
    /// </summary>
    public CarStateManager()
    {
        _stateStore = new Dictionary<string, ICarState>();
    }

    #endregion

    #region Methods

    /// <summary>
    /// Adds a state.
    /// </summary>
    /// <param name="stateId">The state identifier.</param>
    /// <param name="state">The state.</param>
    public void AddState(string stateId, ICarState state)
    {
        // Add the state to the collection
        _stateStore.Add(stateId, state);
    }

    /// <summary>
    /// Changes the state.
    /// </summary>
    /// <param name="stateId">The state identifier.</param>
    public void ChangeState(string stateId)
    {

        // Set thr current state
        CurrentState = _stateStore[stateId];
    }

    #endregion
}

程序

class Program
{
    internal class StateKeys
    {
        public const string Off = "Off";
        public const string Idle = "Idle";
    }

    static void Main(string[] args)
    {
        // Instantiate the state manager
        CarStateManager stateManager = new CarStateManager();

        // Add the states
        stateManager.AddState(StateKeys.Off, new OffState());
        stateManager.AddState(StateKeys.Idle, new IdleState());

        // Change the state and display the message
        stateManager.ChangeState(StateKeys.Off);
        Console.WriteLine(stateManager.CurrentState.Message);

        // Change the state and display the message
        stateManager.ChangeState(StateKeys.Idle);
        Console.WriteLine(stateManager.CurrentState.Message);
        Console.ReadLine();
    }
}

输出：

Off
Idling

HTH！

处理枚举更改方法的更好方法是什么？

6 个答案: