我有以下列举:
public enum AuthenticationMethod
{
FORMS = 1,
WINDOWSAUTHENTICATION = 2,
SINGLESIGNON = 3
}
然而问题是,当我请求AuthenticationMethod时,我需要“FORMS”这个词。表单而不是id
对于这个问题,我找到了以下解决方案(链接):
首先,我需要创建一个自定义属性“StringValue”:
public class StringValue : System.Attribute
{
private readonly string _value;
public StringValue(string value)
{
_value = value;
}
public string Value
{
get { return _value; }
}
}
然后我可以将这个属性添加到我的枚举器中:
public enum AuthenticationMethod
{
[StringValue("FORMS")]
FORMS = 1,
[StringValue("WINDOWS")]
WINDOWSAUTHENTICATION = 2,
[StringValue("SSO")]
SINGLESIGNON = 3
}
当然,我需要一些东西来检索StringValue:
public static class StringEnum
{
public static string GetStringValue(Enum value)
{
string output = null;
Type type = value.GetType();
//Check first in our cached results...
//Look for our 'StringValueAttribute'
//in the field's custom attributes
FieldInfo fi = type.GetField(value.ToString());
StringValue[] attrs =
fi.GetCustomAttributes(typeof(StringValue),
false) as StringValue[];
if (attrs.Length > 0)
{
output = attrs[0].Value;
}
return output;
}
}
很好,现在我已经有了工具来获取枚举器的字符串值。
然后我可以这样使用它:
string valueOfAuthenticationMethod = StringEnum.GetStringValue(AuthenticationMethod.FORMS);
好的,现在所有这些工作就像一个魅力,但我发现它有很多工作。我想知道有没有更好的解决办法。
我还尝试了一些字典和静态属性,但这也不是更好。
试试type-safe-enum模式。
public sealed class AuthenticationMethod {
private readonly String name;
private readonly int value;
public static readonly AuthenticationMethod FORMS = new AuthenticationMethod (1, "FORMS");
public static readonly AuthenticationMethod WINDOWSAUTHENTICATION = new AuthenticationMethod (2, "WINDOWS");
public static readonly AuthenticationMethod SINGLESIGNON = new AuthenticationMethod (3, "SSN");
private AuthenticationMethod(int value, String name){
this.name = name;
this.value = value;
}
public override String ToString(){
return name;
}
}
更新
显式(或隐式)类型转换可以通过
adding static field with mapping
private static readonly Dictionary<string, AuthenticationMethod> instance = new Dictionary<string,AuthenticationMethod>();
n.b. In order that the initialisation of the the "enum member" fields doesn't throw a NullReferenceException when calling the instance constructor, be sure to put the Dictionary field before the "enum member" fields in your class. This is because static field initialisers are called in declaration order, and before the static constructor, creating the weird and necessary but confusing situation that the instance constructor can be called before all static fields have been initialised, and before the static constructor is called.
filling this mapping in instance constructor
instance[name] = this;
and adding user-defined type conversion operator
public static explicit operator AuthenticationMethod(string str)
{
AuthenticationMethod result;
if (instance.TryGetValue(str, out result))
return result;
else
throw new InvalidCastException();
}
可以使用ToString()引用名称而不是值
Console.WriteLine("Auth method: {0}", AuthenticationMethod.Forms.ToString());
文档在这里:
http://msdn.microsoft.com/en-us/library/16c1xs4z.aspx
...如果你在Pascal情况下命名你的枚举(如ThisIsMyEnumValue = 1等),那么你可以使用一个非常简单的正则表达式来打印友好的形式:
static string ToFriendlyCase(this string EnumString)
{
return Regex.Replace(EnumString, "(?!^)([A-Z])", " $1");
}
可以很容易地从任何字符串调用:
Console.WriteLine("ConvertMyCrazyPascalCaseSentenceToFriendlyCase".ToFriendlyCase());
输出:
把我疯狂的帕斯卡格句转换成友好格句
这节省了在房子周围运行创建自定义属性并将它们附加到枚举或使用查找表将枚举值与友好字符串结合,最好的是它是自我管理的,可以用于任何Pascal Case字符串,这是无限可重用的。当然,它不允许您使用与解决方案提供的枚举不同的友好名称。
不过,我确实喜欢你针对更复杂场景的原始解决方案。你可以把你的解决方案更进一步,让你的GetStringValue成为你的枚举的扩展方法,然后你就不需要像StringEnum.GetStringValue…
public static string GetStringValue(this AuthenticationMethod value)
{
string output = null;
Type type = value.GetType();
FieldInfo fi = type.GetField(value.ToString());
StringValue[] attrs = fi.GetCustomAttributes(typeof(StringValue), false) as StringValue[];
if (attrs.Length > 0)
output = attrs[0].Value;
return output;
}
然后你可以直接从你的枚举实例中访问它:
Console.WriteLine(AuthenticationMethod.SSO.GetStringValue());
我真的很喜欢Jakub Šturc的答案,但它的缺点是不能与开关case语句一起使用。下面是他的回答的一个稍微修改的版本,可以与switch语句一起使用:
public sealed class AuthenticationMethod
{
#region This code never needs to change.
private readonly string _name;
public readonly Values Value;
private AuthenticationMethod(Values value, String name){
this._name = name;
this.Value = value;
}
public override String ToString(){
return _name;
}
#endregion
public enum Values
{
Forms = 1,
Windows = 2,
SSN = 3
}
public static readonly AuthenticationMethod FORMS = new AuthenticationMethod (Values.Forms, "FORMS");
public static readonly AuthenticationMethod WINDOWSAUTHENTICATION = new AuthenticationMethod (Values.Windows, "WINDOWS");
public static readonly AuthenticationMethod SINGLESIGNON = new AuthenticationMethod (Values.SSN, "SSN");
}
所以你得到了Jakub Šturc的答案的所有好处,另外我们可以像这样使用switch语句:
var authenticationMethodVariable = AuthenticationMethod.FORMS; // Set the "enum" value we want to use.
var methodName = authenticationMethodVariable.ToString(); // Get the user-friendly "name" of the "enum" value.
// Perform logic based on which "enum" value was chosen.
switch (authenticationMethodVariable.Value)
{
case authenticationMethodVariable.Values.Forms: // Do something
break;
case authenticationMethodVariable.Values.Windows: // Do something
break;
case authenticationMethodVariable.Values.SSN: // Do something
break;
}
当我遇到这样的情况时,我提出下面的解决方案。
作为一个消费阶级,你可以有
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace MyApp.Dictionaries
{
class Greek
{
public static readonly string Alpha = "Alpha";
public static readonly string Beta = "Beta";
public static readonly string Gamma = "Gamma";
public static readonly string Delta = "Delta";
private static readonly BiDictionary<int, string> Dictionary = new BiDictionary<int, string>();
static Greek() {
Dictionary.Add(1, Alpha);
Dictionary.Add(2, Beta);
Dictionary.Add(3, Gamma);
Dictionary.Add(4, Delta);
}
public static string getById(int id){
return Dictionary.GetByFirst(id);
}
public static int getByValue(string value)
{
return Dictionary.GetBySecond(value);
}
}
}
使用双向字典:
基于此(https://stackoverflow.com/a/255638/986160),假设键将与字典中的单个值相关联,类似于(https://stackoverflow.com/a/255630/986160),但更优雅一些。这个字典也是可枚举的,你可以在整型和字符串之间来回切换。此外,除了这个类,你的代码库中不需要有任何字符串。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Collections;
namespace MyApp.Dictionaries
{
class BiDictionary<TFirst, TSecond> : IEnumerable
{
IDictionary<TFirst, TSecond> firstToSecond = new Dictionary<TFirst, TSecond>();
IDictionary<TSecond, TFirst> secondToFirst = new Dictionary<TSecond, TFirst>();
public void Add(TFirst first, TSecond second)
{
firstToSecond.Add(first, second);
secondToFirst.Add(second, first);
}
public TSecond this[TFirst first]
{
get { return GetByFirst(first); }
}
public TFirst this[TSecond second]
{
get { return GetBySecond(second); }
}
public TSecond GetByFirst(TFirst first)
{
return firstToSecond[first];
}
public TFirst GetBySecond(TSecond second)
{
return secondToFirst[second];
}
public IEnumerator GetEnumerator()
{
return GetFirstEnumerator();
}
public IEnumerator GetFirstEnumerator()
{
return firstToSecond.GetEnumerator();
}
public IEnumerator GetSecondEnumerator()
{
return secondToFirst.GetEnumerator();
}
}
}
不幸的是,在枚举上获取属性的反射非常慢:
看这个问题:有人知道一种快速获取枚举值的自定义属性的方法吗?
. tostring()在枚举上也相当慢。
你可以为枚举写扩展方法:
public static string GetName( this MyEnum input ) {
switch ( input ) {
case MyEnum.WINDOWSAUTHENTICATION:
return "Windows";
//and so on
}
}
这不是很好,但是很快,而且不需要对属性或字段名进行反射。
c# 6更新
如果你可以使用c# 6,那么操作符的新名称适用于枚举,因此nameof(myenume .WINDOWSAUTHENTICATION)将在编译时转换为“WINDOWSAUTHENTICATION”,使其成为获取枚举名称的最快方式。
注意,这将显式枚举转换为内联常量,因此它不适用于变量中的枚举。所以:
nameof(AuthenticationMethod.FORMS) == "FORMS"
但是…
var myMethod = AuthenticationMethod.FORMS;
nameof(myMethod) == "myMethod"