从混淆中解析枚举中获取
这是创建.NET的人员的决定。枚举被另一个值类型（备份int，short，byte，等），所以它实际上可以有一个有效期为那些值类型的任意值。
我个人不喜欢这种方式，所以我提出了一系列实用方法：
/// <summary>
/// Utility methods for enum values. This static type will fail to initialize
/// (throwing a <see cref="TypeInitializationException"/>) if
/// you try to provide a value that is not an enum.
/// </summary>
/// <typeparam name="T">An enum type. </typeparam>
public static class EnumUtil<T>
where T : struct, IConvertible // Try to get as much of a static check as we can.
{
// The .NET framework doesn't provide a compile-checked
// way to ensure that a type is an enum, so we have to check when the type
// is statically invoked.
static EnumUtil()
{
// Throw Exception on static initialization if the given type isn't an enum.
Require.That(typeof (T).IsEnum, () => typeof(T).FullName + " is not an enum type.");
}
/// <summary>
/// In the .NET Framework, objects can be cast to enum values which are not
/// defined for their type. This method provides a simple fail-fast check
/// that the enum value is defined, and creates a cast at the same time.
/// Cast the given value as the given enum type.
/// Throw an exception if the value is not defined for the given enum type.
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="enumValue"></param>
/// <exception cref="InvalidCastException">
/// If the given value is not a defined value of the enum type.
/// </exception>
/// <returns></returns>
public static T DefinedCast(object enumValue)
{
if (!System.Enum.IsDefined(typeof(T), enumValue))
throw new InvalidCastException(enumValue + " is not a defined value for enum type " +
typeof (T).FullName);
return (T) enumValue;
}
/// <summary>
///
/// </summary>
/// <param name="enumValue"></param>
/// <returns></returns>
public static T Parse(string enumValue)
{
var parsedValue = (T)System.Enum.Parse(typeof (T), enumValue);
//Require that the parsed value is defined
Require.That(parsedValue.IsDefined(),
() => new ArgumentException(string.Format("{0} is not a defined value for enum type {1}",
enumValue, typeof(T).FullName)));
return parsedValue;
}
public static bool IsDefined(T enumValue)
{
return System.Enum.IsDefined(typeof (T), enumValue);
}
}
public static class EnumExtensions
{
public static bool IsDefined<T>(this T enumValue)
where T : struct, IConvertible
{
return EnumUtil<T>.IsDefined(enumValue);
}
}
这样，我可以说：
if(!sEnum.IsDefined()) throw new Exception(...);
... 要么：
EnumUtil<Stooge>.Parse(s); // throws an exception if s is not a defined value.
编辑
除了上面给出的解释之外，您还必须意识到Enum的.NET版本遵循的样式比受Java启发的样式更受C启发。这样就可以拥有“位标志”枚举，该枚举可以使用二进制模式来确定某个特定“标志”在枚举值中是否处于活动状态。如果你必须定义标志的每一个可能的组合（即MondayAndTuesday，MondayAndWednesdayAndThursday），这将是非常乏味的。因此，具有使用未定义的枚举值的能力非常方便。当您想要对不利用这些技巧的枚举类型执行快速失败操作时，只需要做一些额外的工作。