我读过一些SO帖子，似乎最基本的操作都缺失了。
public enum LoggingLevel
{
Off = 0,
Error = 1,
Warning = 2,
Info = 3,
Debug = 4,
Trace = 5
};
if (s == "LogLevel")
{
_log.LogLevel = (LoggingLevel)Convert.ToInt32("78");
_log.LogLevel = (LoggingLevel)Enum.Parse(typeof(LoggingLevel), "78");
_log.WriteDebug(_log.LogLevel.ToString());
}
这不会导致异常，它很乐意存储78。是否有一种方法来验证进入枚举的值?
当前回答
规范的答案是Enum。IsDefined，但这是a:在一个紧密循环中使用有点慢，b:对[Flags]枚举无效。
就我个人而言，我不会再担心这个问题，只要适当地转换一下，记住:
如果不识别所有内容(只是不做任何事情)是可以的，那么就不要添加默认值:(或使用空默认值:解释原因) 如果有一个明智的默认行为，把它放在默认: 否则，处理你知道的那些，并对其余的抛出异常:
像这样:
switch(someflag) {
case TriBool.Yes:
DoSomething();
break;
case TriBool.No:
DoSomethingElse();
break;
case TriBool.FileNotFound:
DoSomethingOther();
break;
default:
throw new ArgumentOutOfRangeException("someflag");
}
其他回答
一种方法是依赖于强制转换和枚举到字符串的转换。当将int转换为Enum类型时，int要么被转换为相应的Enum值，要么如果没有为int定义Enum值，则结果Enum仅包含int作为值。
enum NetworkStatus{
Unknown=0,
Active,
Slow
}
int statusCode=2;
NetworkStatus netStatus = (NetworkStatus) statusCode;
bool isDefined = netStatus.ToString() != statusCode.ToString();
没有对任何边缘情况进行测试。
上述解决方案不处理[Flags]情况。
我下面的解决方案可能会有一些性能问题(我相信可以以各种方式进行优化)，但本质上它总是证明enum值是否有效。
它依赖于三个假设:
c#中的枚举值只允许是int型，绝对不能是其他类型 c#中的枚举名称必须以字母字符开头 无效的枚举名称不能带有负号:-
在一个enum上调用ToString()，如果没有匹配的enum(是否有标志)，则返回int值。如果匹配了一个允许的enum值，它将打印匹配项的名称。
So:
[Flags]
enum WithFlags
{
First = 1,
Second = 2,
Third = 4,
Fourth = 8
}
((WithFlags)2).ToString() ==> "Second"
((WithFlags)(2 + 4)).ToString() ==> "Second, Third"
((WithFlags)20).ToString() ==> "20"
记住这两条规则，我们可以假设如果.NET Framework正确地完成了它的工作，任何对有效enum的ToString()方法的调用都将导致一个以字母字符为第一个字符的东西:
public static bool IsValid<TEnum>(this TEnum enumValue)
where TEnum : struct
{
var firstChar = enumValue.ToString()[0];
return (firstChar < '0' || firstChar > '9') && firstChar != '-';
}
有人可以称之为“黑客”，但其优点是，通过依赖微软自己的Enum和c#标准实现，您不必依赖自己可能存在bug的代码或检查。在性能不是特别关键的情况下，这将节省大量讨厌的开关语句或其他检查!
Edit
感谢@ChaseMedallion指出我最初的实现不支持负值。这已得到补救，并提供了测试。
以及支持它的测试:
[TestClass]
public class EnumExtensionsTests
{
[Flags]
enum WithFlags
{
First = 1,
Second = 2,
Third = 4,
Fourth = 8
}
enum WithoutFlags
{
First = 1,
Second = 22,
Third = 55,
Fourth = 13,
Fifth = 127
}
enum WithoutNumbers
{
First, // 1
Second, // 2
Third, // 3
Fourth // 4
}
enum WithoutFirstNumberAssigned
{
First = 7,
Second, // 8
Third, // 9
Fourth // 10
}
enum WithNagativeNumbers
{
First = -7,
Second = -8,
Third = -9,
Fourth = -10
}
[TestMethod]
public void IsValidEnumTests()
{
Assert.IsTrue(((WithFlags)(1 | 4)).IsValid());
Assert.IsTrue(((WithFlags)(1 | 4)).IsValid());
Assert.IsTrue(((WithFlags)(1 | 4 | 2)).IsValid());
Assert.IsTrue(((WithFlags)(2)).IsValid());
Assert.IsTrue(((WithFlags)(3)).IsValid());
Assert.IsTrue(((WithFlags)(1 + 2 + 4 + 8)).IsValid());
Assert.IsFalse(((WithFlags)(16)).IsValid());
Assert.IsFalse(((WithFlags)(17)).IsValid());
Assert.IsFalse(((WithFlags)(18)).IsValid());
Assert.IsFalse(((WithFlags)(0)).IsValid());
Assert.IsTrue(((WithoutFlags)1).IsValid());
Assert.IsTrue(((WithoutFlags)22).IsValid());
Assert.IsTrue(((WithoutFlags)(53 | 6)).IsValid()); // Will end up being Third
Assert.IsTrue(((WithoutFlags)(22 | 25 | 99)).IsValid()); // Will end up being Fifth
Assert.IsTrue(((WithoutFlags)55).IsValid());
Assert.IsTrue(((WithoutFlags)127).IsValid());
Assert.IsFalse(((WithoutFlags)48).IsValid());
Assert.IsFalse(((WithoutFlags)50).IsValid());
Assert.IsFalse(((WithoutFlags)(1 | 22)).IsValid());
Assert.IsFalse(((WithoutFlags)(9 | 27 | 4)).IsValid());
Assert.IsTrue(((WithoutNumbers)0).IsValid());
Assert.IsTrue(((WithoutNumbers)1).IsValid());
Assert.IsTrue(((WithoutNumbers)2).IsValid());
Assert.IsTrue(((WithoutNumbers)3).IsValid());
Assert.IsTrue(((WithoutNumbers)(1 | 2)).IsValid()); // Will end up being Third
Assert.IsTrue(((WithoutNumbers)(1 + 2)).IsValid()); // Will end up being Third
Assert.IsFalse(((WithoutNumbers)4).IsValid());
Assert.IsFalse(((WithoutNumbers)5).IsValid());
Assert.IsFalse(((WithoutNumbers)25).IsValid());
Assert.IsFalse(((WithoutNumbers)(1 + 2 + 3)).IsValid());
Assert.IsTrue(((WithoutFirstNumberAssigned)7).IsValid());
Assert.IsTrue(((WithoutFirstNumberAssigned)8).IsValid());
Assert.IsTrue(((WithoutFirstNumberAssigned)9).IsValid());
Assert.IsTrue(((WithoutFirstNumberAssigned)10).IsValid());
Assert.IsFalse(((WithoutFirstNumberAssigned)11).IsValid());
Assert.IsFalse(((WithoutFirstNumberAssigned)6).IsValid());
Assert.IsFalse(((WithoutFirstNumberAssigned)(7 | 9)).IsValid());
Assert.IsFalse(((WithoutFirstNumberAssigned)(8 + 10)).IsValid());
Assert.IsTrue(((WithNagativeNumbers)(-7)).IsValid());
Assert.IsTrue(((WithNagativeNumbers)(-8)).IsValid());
Assert.IsTrue(((WithNagativeNumbers)(-9)).IsValid());
Assert.IsTrue(((WithNagativeNumbers)(-10)).IsValid());
Assert.IsFalse(((WithNagativeNumbers)(-11)).IsValid());
Assert.IsFalse(((WithNagativeNumbers)(7)).IsValid());
Assert.IsFalse(((WithNagativeNumbers)(8)).IsValid());
}
}
正如其他人所说，Enum。IsDefined返回false，即使你有一个用FlagsAttribute装饰的enum的有效的位标志组合。
遗憾的是，创建一个为有效位标志返回true的方法有点长:
public static bool ValidateEnumValue<T>(T value) where T : Enum
{
// Check if a simple value is defined in the enum.
Type enumType = typeof(T);
bool valid = Enum.IsDefined(enumType, value);
// For enums decorated with the FlagsAttribute, allow sets of flags.
if (!valid && enumType.GetCustomAttributes(typeof(FlagsAttribute), false)?.Any() == true)
{
long mask = 0;
foreach (object definedValue in Enum.GetValues(enumType))
mask |= Convert.ToInt64(definedValue);
long longValue = Convert.ToInt64(value);
valid = (mask & longValue) == longValue;
}
return valid;
}
你可能想把GetCustomAttribute的结果缓存到一个字典中:
private static readonly Dictionary<Type, bool> _flagEnums = new Dictionary<Type, bool>();
public static bool ValidateEnumValue<T>(T value) where T : Enum
{
// Check if a simple value is defined in the enum.
Type enumType = typeof(T);
bool valid = Enum.IsDefined(enumType, value);
if (!valid)
{
// For enums decorated with the FlagsAttribute, allow sets of flags.
if (!_flagEnums.TryGetValue(enumType, out bool isFlag))
{
isFlag = enumType.GetCustomAttributes(typeof(FlagsAttribute), false)?.Any() == true;
_flagEnums.Add(enumType, isFlag);
}
if (isFlag)
{
long mask = 0;
foreach (object definedValue in Enum.GetValues(enumType))
mask |= Convert.ToInt64(definedValue);
long longValue = Convert.ToInt64(value);
valid = (mask & longValue) == longValue;
}
}
return valid;
}
注意，上面的代码在T上使用了新的Enum约束，这是c# 7.3以来才有的。您需要在旧版本中传递一个对象值，并对其调用GetType()。
签出Enum。IsDefined
用法:
if(Enum.IsDefined(typeof(MyEnum), value))
MyEnum a = (MyEnum)value;
这是那一页的例子:
using System;
[Flags] public enum PetType
{
None = 0, Dog = 1, Cat = 2, Rodent = 4, Bird = 8, Reptile = 16, Other = 32
};
public class Example
{
public static void Main()
{
object value;
// Call IsDefined with underlying integral value of member.
value = 1;
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
// Call IsDefined with invalid underlying integral value.
value = 64;
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
// Call IsDefined with string containing member name.
value = "Rodent";
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
// Call IsDefined with a variable of type PetType.
value = PetType.Dog;
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
value = PetType.Dog | PetType.Cat;
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
// Call IsDefined with uppercase member name.
value = "None";
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
value = "NONE";
Console.WriteLine("{0}: {1}", value, Enum.IsDefined(typeof(PetType), value));
// Call IsDefined with combined value
value = PetType.Dog | PetType.Bird;
Console.WriteLine("{0:D}: {1}", value, Enum.IsDefined(typeof(PetType), value));
value = value.ToString();
Console.WriteLine("{0:D}: {1}", value, Enum.IsDefined(typeof(PetType), value));
}
}
使用实例显示如下信息:
// 1: True
// 64: False
// Rodent: True
// Dog: True
// Dog, Cat: False
// None: True
// NONE: False
// 9: False
// Dog, Bird: False
使用Enum.IsDefined。
