在c#中扩展枚举

Question

在java中我用来扩展枚举值或重写这样的方法:

    enum SomeEnum
    {

        option1("sv")
        {
            public String toString()
            {
                return "Some value";
            }     
        }, 
        option2;

        private String PassedValue;

        public SomeEnum(String somevalue)
        {
            this.PassedValue = somevalue;
        }

        public SomeEnum()
        {
                this.PassedValue = "Default Value";
        }

        public String getPassedValue()
        {
            return this.PassedValue;
        }

    }

有没有办法在c#中做类似的事情,或者c#中的枚举更有限

Answer 1

我希望枚解在.Net中更强大.我喜欢.Net!您可以使用属性来完成同样的事情.写下面的代码一次,到处使用它.这将是一个很长的答案,但我认为这是一个非常好的解决方案,所以要有耐心!

用法

SomeEnum e = SomeEnum.ValueTwo;
string description = e.GetDescription();

恩欧姆

使用属性来描述枚举及其值.

[DescriptiveEnumEnforcement(DescriptiveEnumEnforcement.EnforcementTypeEnum.ThrowException)]
public enum SomeEnum
{
    [Description("Value One")]
    ValueOne,

    [Description("Value Two")]
    ValueTwo,

    [Description("Value 3")]
    ValueThree
}

DescriptionAttribute

/// <summary>Indicates that an enum value has a description.</summary>
[AttributeUsage(AttributeTargets.Field)]
public class DescriptionAttribute : System.Attribute
{
    /// <summary>The description for the enum value.</summary>
    public string Description { get; set; }

    /// <summary>Constructs a new DescriptionAttribute.</summary>
    public DescriptionAttribute() { }

    /// <summary>Constructs a new DescriptionAttribute.</summary>
    /// <param name="description">The initial value of the Description property.</param>
    public DescriptionAttribute(string description)
    {
        this.Description = description;
    }

    /// <summary>Returns the Description property.</summary>
    /// <returns>The Description property.</returns>
    public override string ToString()
    {
        return this.Description;
    }
}

DescriptiveEnumEnforcementAttribute

确保正确配置枚举的属性.

/// <summary>Indicates whether or not an enum must have a NameAttribute and a DescriptionAttribute.</summary>
[AttributeUsage(AttributeTargets.Enum)]
public class DescriptiveEnumEnforcementAttribute : System.Attribute
{
    /// <summary>Defines the different types of enforcement for DescriptiveEnums.</summary>
    public enum EnforcementTypeEnum
    {
        /// <summary>Indicates that the enum must have a NameAttribute and a DescriptionAttribute.</summary>
        ThrowException,

        /// <summary>Indicates that the enum does not have a NameAttribute and a DescriptionAttribute, the value will be used instead.</summary>
        DefaultToValue
    }

    /// <summary>The enforcement type for this DescriptiveEnumEnforcementAttribute.</summary>
    public EnforcementTypeEnum EnforcementType { get; set; }

    /// <summary>Constructs a new DescriptiveEnumEnforcementAttribute.</summary>
    public DescriptiveEnumEnforcementAttribute()
    {
        this.EnforcementType = EnforcementTypeEnum.DefaultToValue;
    }

    /// <summary>Constructs a new DescriptiveEnumEnforcementAttribute.</summary>
    /// <param name="enforcementType">The initial value of the EnforcementType property.</param>
    public DescriptiveEnumEnforcementAttribute(EnforcementTypeEnum enforcementType)
    {
        this.EnforcementType = enforcementType;
    }
}

获得描述

/// <summary>Provides functionality to enhance enumerations.</summary>
public static partial class EnumUtil
{
    /// <summary>Returns the description of the specified enum.</summary>
    /// <param name="value">The value of the enum for which to return the description.</param>
    /// <returns>A description of the enum, or the enum name if no description exists.</returns>
    public static string GetDescription(this Enum value)
    {
        return GetEnumDescription(value);
    }

    /// <summary>Returns the description of the specified enum.</summary>
    /// <param name="value">The value of the enum for which to return the description.</param>
    /// <returns>A description of the enum, or the enum name if no description exists.</returns>
    public static string GetDescription<T>(object value)
    {
        return GetEnumDescription(value);
    }

    /// <summary>Returns the description of the specified enum.</summary>
    /// <param name="value">The value of the enum for which to return the description.</param>
    /// <returns>A description of the enum, or the enum name if no description exists.</returns>
    public static string GetEnumDescription(object value)
    {
        if (value == null)
        return null;

        Type type = value.GetType();

        //Make sure the object is an enum.
        if (!type.IsEnum)
            throw new ApplicationException("Value parameter must be an enum.");

        FieldInfo fieldInfo = type.GetField(value.ToString());
        object[] descriptionAttributes = fieldInfo.GetCustomAttributes(typeof(DescriptionAttribute), false);

        //If no DescriptionAttribute exists for this enum value, check the DescriptiveEnumEnforcementAttribute and decide how to proceed.
        if (descriptionAttributes == null || descriptionAttributes.Length == 0)
        {
            object[] enforcementAttributes = fieldInfo.GetCustomAttributes(typeof(DescriptiveEnumEnforcementAttribute), false);

            //If a DescriptiveEnumEnforcementAttribute exists, either throw an exception or return the name of the enum instead.
            if (enforcementAttributes != null && enforcementAttributes.Length == 1)
            {
                DescriptiveEnumEnforcementAttribute enforcementAttribute = (DescriptiveEnumEnforcementAttribute)enforcementAttributes[0];

                if (enforcementAttribute.EnforcementType == DescriptiveEnumEnforcementAttribute.EnforcementTypeEnum.ThrowException)
                    throw new ApplicationException("No Description attributes exist in enforced enum of type '" + type.Name + "', value '" + value.ToString() + "'.");

                return GetEnumName(value);
            }
            else //Just return the name of the enum.
                return GetEnumName(value);
        }
        else if (descriptionAttributes.Length > 1)
            throw new ApplicationException("Too many Description attributes exist in enum of type '" + type.Name + "', value '" + value.ToString() + "'.");

        //Return the value of the DescriptionAttribute.
        return descriptionAttributes[0].ToString();
    }
}

Answer 2

C#中的枚举仅适用于(整数)值; 他们不能像Java那样拥有特殊的方法或构造函数.

但是,您可以定义对枚举起作用的扩展方法,以实现几乎相同的效果:

public enum MyEnum {
    Foo = 1,
    Bar = 2,
    Default = Foo
}

public static class MyEnumExtensions
{
    public static Widget ToWidget(this MyEnum enumValue) {
        switch (enumValue) {
        case MyEnum.Foo:
            return new Widget("Foo!");

        case MyEnum.Bar:
            return new Widget("Bar...");

        default:
            return null;
        }
    }
}

然后你可以说:

var val = MyEnum.Foo;
var widget = val.ToWidget();