为什么将int转换为无效枚举值不抛出异常？
为什么将int转换为无效枚举值不抛出异常？
提问于 2011-06-20 23:38:20
如果我有一个像这样的枚举：
enum Beer
{
Bud = 10,
Stella = 20,
Unknown
}当将这些值之外的int转换为Beer类型时，它为什么不引发异常
例如，下面的代码没有抛出异常，它将'50‘输出到控制台：
int i = 50;
var b = (Beer) i;
Console.WriteLine(b.ToString());我发现这个strange...can有人澄清了吗？
回答 1
Stack Overflow用户
回答已采纳
发布于 2011-06-20 23:41:17
摘自Confusion with parsing an Enum
这是创建.NET的人的决定，枚举由另一个值类型(int、short、byte等)支持，因此它实际上可以具有对这些值类型有效的任何值。
我个人并不喜欢这种工作方式，所以我做了一系列实用的方法：
/// <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(...);..。或者：
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，您还必须认识到，.NET版本的枚举遵循的是一种更受C语言启发的模式。这使得可以使用二进制模式来确定特定“标志”在枚举值中是否有效的"Bit Flag" enums成为可能。如果你必须定义每种可能的标志组合(例如MondayAndTuesday、MondayAndWednesdayAndThursday)，这些将是非常繁琐的。因此，能够使用未定义的枚举值是非常方便的。当您想要在不利用这些技巧的枚举类型上执行快速失败行为时，只需要做一些额外的工作。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/6413804
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