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2025-01-12 05:00:06

是否有一种方法来检查是否int是合法的enum在c# ?

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

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());
    }
}
2014-04-20 01:55:17

其他回答

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());
    }
}
2014-04-20 01:55:17

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");
}
2010-04-20 11:58:10

Use:

Enum.IsDefined ( typeof ( Enum ), EnumValue );
2010-04-20 11:48:28

使用Enum.IsDefined。

2010-04-20 11:47:57

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。

2015-01-13 12:33:15

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