211

假设我有这个枚举:

[Flags]
enum Letters
{
     A = 1,
     B = 2,
     C = 4,
     AB = A | B,
     All = A | B | C,
}

要检查例如AB是否已设置,我可以这样做:

if((letter & Letters.AB) == Letters.AB)

是否有比以下更简单的方法来检查是否设置了组合标志常量的任何标志?

if((letter & Letters.A) == Letters.A || (letter & Letters.B) == Letters.B)

例如可以&用一些东西交换吗?

4

18 回答 18

207

在 .NET 4 中,您可以使用Enum.HasFlag 方法

using System;

[Flags] public enum Pet {
   None = 0,
   Dog = 1,
   Cat = 2,
   Bird = 4,
   Rabbit = 8,
   Other = 16
}

public class Example
{
   public static void Main()
   {
      // Define three families: one without pets, one with dog + cat and one with a dog only
      Pet[] petsInFamilies = { Pet.None, Pet.Dog | Pet.Cat, Pet.Dog };
      int familiesWithoutPets = 0;
      int familiesWithDog = 0;

      foreach (Pet petsInFamily in petsInFamilies)
      {
         // Count families that have no pets. 
         if (petsInFamily.Equals(Pet.None))
            familiesWithoutPets++;
         // Of families with pets, count families that have a dog. 
         else if (petsInFamily.HasFlag(Pet.Dog))
            familiesWithDog++;
      }
      Console.WriteLine("{0} of {1} families in the sample have no pets.", 
                        familiesWithoutPets, petsInFamilies.Length);   
      Console.WriteLine("{0} of {1} families in the sample have a dog.", 
                        familiesWithDog, petsInFamilies.Length);   
   }
}

该示例显示以下输出:

//       1 of 3 families in the sample have no pets. 
//       2 of 3 families in the sample have a dog.
于 2012-03-20T04:10:19.960 回答
172

如果您想知道 letter 是否包含 AB 中的任何字母,您必须使用AND &运算符。就像是:

if ((letter & Letters.AB) != 0)
{
    // Some flag (A,B or both) is enabled
}
else
{
    // None of them are enabled
}
于 2009-08-27T09:48:58.437 回答
65

我使用扩展方法来写这样的东西:

if (letter.IsFlagSet(Letter.AB))
    ...

这是代码:

public static class EnumExtensions
{
    private static void CheckIsEnum<T>(bool withFlags)
    {
        if (!typeof(T).IsEnum)
            throw new ArgumentException(string.Format("Type '{0}' is not an enum", typeof(T).FullName));
        if (withFlags && !Attribute.IsDefined(typeof(T), typeof(FlagsAttribute)))
            throw new ArgumentException(string.Format("Type '{0}' doesn't have the 'Flags' attribute", typeof(T).FullName));
    }

    public static bool IsFlagSet<T>(this T value, T flag) where T : struct
    {
        CheckIsEnum<T>(true);
        long lValue = Convert.ToInt64(value);
        long lFlag = Convert.ToInt64(flag);
        return (lValue & lFlag) != 0;
    }

    public static IEnumerable<T> GetFlags<T>(this T value) where T : struct
    {
        CheckIsEnum<T>(true);
        foreach (T flag in Enum.GetValues(typeof(T)).Cast<T>())
        {
            if (value.IsFlagSet(flag))
                yield return flag;
        }
    }

    public static T SetFlags<T>(this T value, T flags, bool on) where T : struct
    {
        CheckIsEnum<T>(true);
        long lValue = Convert.ToInt64(value);
        long lFlag = Convert.ToInt64(flags);
        if (on)
        {
            lValue |= lFlag;
        }
        else
        {
            lValue &= (~lFlag);
        }
        return (T)Enum.ToObject(typeof(T), lValue);
    }

    public static T SetFlags<T>(this T value, T flags) where T : struct
    {
        return value.SetFlags(flags, true);
    }

    public static T ClearFlags<T>(this T value, T flags) where T : struct
    {
        return value.SetFlags(flags, false);
    }

    public static T CombineFlags<T>(this IEnumerable<T> flags) where T : struct
    {
        CheckIsEnum<T>(true);
        long lValue = 0;
        foreach (T flag in flags)
        {
            long lFlag = Convert.ToInt64(flag);
            lValue |= lFlag;
        }
        return (T)Enum.ToObject(typeof(T), lValue);
    }

    public static string GetDescription<T>(this T value) where T : struct
    {
        CheckIsEnum<T>(false);
        string name = Enum.GetName(typeof(T), value);
        if (name != null)
        {
            FieldInfo field = typeof(T).GetField(name);
            if (field != null)
            {
                DescriptionAttribute attr = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute)) as DescriptionAttribute;
                if (attr != null)
                {
                    return attr.Description;
                }
            }
        }
        return null;
    }
}
于 2009-08-27T10:08:54.387 回答
42

.NET 4 或更高版本中有HasFlag方法。

if(letter.HasFlag(Letters.AB))
{
}
于 2013-06-24T10:54:23.687 回答
34

如果您可以使用 .NET 4 或更高版本,请使用 HasFlag() 方法

例子

letter.HasFlag(Letters.A | Letters.B) // both A and B must be set

如同

letter.HasFlag(Letters.AB)
于 2014-12-24T13:45:02.490 回答
14

如果它真的让你烦恼,你可以写一个这样的函数:

public bool IsSet(Letters value, Letters flag)
{
    return (value & flag) == flag;
}

if (IsSet(letter, Letters.A))
{
   // ...
}

// If you want to check if BOTH Letters.A and Letters.B are set:
if (IsSet(letter, Letters.A & Letters.B))
{
   // ...
}

// If you want an OR, I'm afraid you will have to be more verbose:
if (IsSet(letter, Letters.A) || IsSet(letter, Letters.B))
{
   // ...
}
于 2009-08-27T09:48:24.927 回答
11

要检查例如 AB 是否设置,我可以这样做:

if((字母 & Letters.AB) == Letters.AB)

是否有比以下更简单的方法来检查是否设置了组合标志常量的任何标志?

这将检查是否设置A 和 B,并忽略是否设置了任何其他标志。

if((letter & Letters.A) == Letters.A || (letter & Letters.B) == Letters.B)

这会检查是否设置A 或 B,并忽略是否设置了任何其他标志。

这可以简化为:

if(letter & Letters.AB)

这是二进制操作的C;将其应用于 C# 应该很简单:

enum {
     A = 1,
     B = 2,
     C = 4,
     AB = A | B,
     All = AB | C,
};

int flags = A|C;

bool anything_and_a = flags & A;

bool only_a = (flags == A);

bool a_and_or_c_and_anything_else = flags & (A|C);

bool both_ac_and_anything_else = (flags & (A|C)) == (A|C);

bool only_a_and_c = (flags == (A|C));

顺便说一句,问题示例中变量的命名是单数“字母”,这可能意味着它仅代表一个字母;示例代码清楚地表明它是一组可能的字母并且允许多个值,因此请考虑重命名变量“字母”。

于 2009-08-27T09:53:58.770 回答
5

我创建了一个不需要检查Enum类型的简单扩展方法:

public static bool HasAnyFlag(this Enum value, Enum flags)
{
    return
        value != null && ((Convert.ToInt32(value) & Convert.ToInt32(flags)) != 0);
}

它也适用于可为空的枚举。标准HasFlag方法没有,所以我也创建了一个扩展来涵盖它。

public static bool HasFlag(this Enum value, Enum flags)
{
    int f = Convert.ToInt32(flags);

    return
        value != null && ((Convert.ToInt32(value) & f) == f);
}

一个简单的测试:

[Flags]
enum Option
{
    None = 0x00,
    One = 0x01,
    Two = 0x02,
    Three = One | Two,
    Four = 0x04
}

[TestMethod]
public void HasAnyFlag()
{
    Option o1 = Option.One;
    Assert.AreEqual(true, o1.HasAnyFlag(Option.Three));
    Assert.AreEqual(false, o1.HasFlag(Option.Three));

    o1 |= Option.Two;
    Assert.AreEqual(true, o1.HasAnyFlag(Option.Three));
    Assert.AreEqual(true, o1.HasFlag(Option.Three));
}

[TestMethod]
public void HasAnyFlag_NullableEnum()
{
    Option? o1 = Option.One;
    Assert.AreEqual(true, o1.HasAnyFlag(Option.Three));
    Assert.AreEqual(false, o1.HasFlag(Option.Three));

    o1 |= Option.Two;
    Assert.AreEqual(true, o1.HasAnyFlag(Option.Three));
    Assert.AreEqual(true, o1.HasFlag(Option.Three));
}

享受!

于 2015-05-06T08:26:40.397 回答
5

这里有很多答案,但我认为使用标志最惯用的方法是 Letters.AB.HasFlag(letter) 或 (Letters.A | Letters.B).HasFlag(letter) 如果你没有已经有 Letters.AB。letter.HasFlag(Letters.AB) 仅在两者兼有时才有效。

于 2015-09-24T21:46:18.243 回答
4

怎么样

if ((letter & Letters.AB) > 0)

?

于 2009-08-27T09:48:07.813 回答
4

您可以在枚举上使用此扩展方法,用于任何类型的枚举:

public static bool IsSingle(this Enum value)
{
    var items = Enum.GetValues(value.GetType());
    var counter = 0;
    foreach (var item in items)
    {
        if (value.HasFlag((Enum)item))
        {
            counter++;
        }
        if (counter > 1)
        {
            return false;
        }
    }
    return true;
}
于 2016-09-28T07:14:40.900 回答
3

这对你有用吗?

if ((letter & (Letters.A | Letters.B)) != 0)
于 2009-08-27T09:51:20.973 回答
0
if((int)letter != 0) { }
于 2009-08-27T09:47:44.570 回答
0

您可以检查该值是否不为零。

if ((Int32)(letter & Letters.AB) != 0) { }

但我认为引入一个值为 0 的新枚举值并与该枚举值进行比较是更好的解决方案(如果可能,因为您必须能够修改枚举)。

[Flags]
enum Letters
{
    None = 0,
    A    = 1,
    B    = 2,
    C    = 4,
    AB   =  A | B,
    All  = AB | C
}

if (letter != Letters.None) { }

更新

误读了问题 - 修正了第一个建议,而忽略了第二个建议。

于 2009-08-27T09:56:55.410 回答
0

我可以看到有两种方法可以用于检查是否设置了任何位。

方法 A

if (letter != 0)
{
}

只要您不介意检查所有位,包括未定义的位,这将起作用!

方法 B

if ((letter & Letters.All) != 0)
{
}

这只检查定义的位,只要 Letters.All 代表所有可能的位。

对于特定位(一组或多组),使用方法 B 将 Letters.All 替换为您要检查的位(见下文)。

if ((letter & Letters.AB) != 0)
{
}
于 2009-08-27T10:01:49.783 回答
0

从 .Net 4 开始,您可以使用简写版本而无需明确指定 &:

if(Letters.AB.HasFlag(Letters.C))
于 2021-02-27T08:34:49.163 回答
0

我们能否轻松有效地找出是否设置了至少一个标志

好吧,如果您对检查是否至少设置了一个标志感到满意,那么是的!

用法:

if (EnumHelper.HasAnyFlagBitsSet(letter))

执行:

public static class EnumHelper
{
    static EnumHelper()
    {
        // Required to get correct behavior in GetNumericValue
        // Because we will overlap the enum type with a ulong, left-aligned
        if (!BitConverter.IsLittleEndian)
            throw new NotSupportedException("This type is only supported on little-endian architectures.");
    }

    /// <summary>
    /// <para>
    /// Returns whether the given enum value has any bits set that occurs in a defined flag for <typeparamref name="T"/>.
    /// </para>
    /// <para>
    /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>.
    /// </para>
    /// </summary>
    public static bool HasAnyFlagBitsSet<T>(T enumValue)
        where T : unmanaged, Enum
    {
        var numericValue = GetNumericValue(enumValue);

        // Take the value that has all the permitted bits set
        // Use & to keep only the corresponding bits from the input value
        // Check that the input value provided at least one such bit
        return (numericValue & FlagValueCache<T>.AllFlagsSetValue) != 0;
    }

    /// <summary>
    /// <para>
    /// Returns whether the given enum value has any bits set that are set in <paramref name="flags"/>.
    /// </para>
    /// <para>
    /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>.
    /// </para>
    /// </summary>
    public static bool HasAnyFlagBitsSet<T>(T enumValue, T flags)
        where T : unmanaged, Enum
    {
        var numericValue = GetNumericValue(enumValue);
        var numericFlags = GetNumericValue(flags);

        // Use & to keep only the bits present in flags
        // Check that the input value provided at least one such bit
        return (numericValue & flags) != 0;
    }

    // Actually, have a bonus method as well, since this is a common operation:

    /// <summary>
    /// <para>
    /// Returns whether the given enum value consists exclusively of defined flags for <typeparamref name="T"/>.
    /// The result is false if a bit is set that is not part of any value defined by <typeparamref name="T"/>.
    /// </para>
    /// <para>
    /// Throws if the type parameter is not an enum type with the <see cref="FlagsAttribute"/>.
    /// </para>
    /// </summary>
    public static bool HasDefinedFlags<T>(T enumValue)
        where T : unmanaged, Enum
    {
        var numericValue = GetNumericValue(enumValue);

        // Take the value that has all the permitted bits set
        // Use ~ to get a value with all the forbidden bits set
        // Use & to keep only the corresponding bits from the input value
        // Check that the input value provided no such forbidden bits
        return (numericValue & ~FlagValueCache<T>.AllFlagsSetValue) == 0;
    }

    /// <summary>
    /// <para>
    /// Returns the numeric value of the given <paramref name="enumValue"/>.
    /// </para>
    /// <para>
    /// The resulting <see cref="ulong"/> can be cast to the intended integral type, even if it is a signed type.
    /// </para>
    /// </summary>
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public static ulong GetNumericValue<T>(T enumValue)
        where T : unmanaged, Enum
    {
        Span<ulong> ulongSpan = stackalloc ulong[] { 0UL };
        Span<T> span = MemoryMarshal.Cast<ulong, T>(ulongSpan);

        span[0] = enumValue;

        return ulongSpan[0];
    }

    /// <summary>
    /// Statically caches a "full" flags value each enum type for which this class is accessed.
    /// </summary>
    internal static class FlagValueCache<T>
        where T : unmanaged, Enum
    {
        /// <summary>
        /// Each bit that is set in any of the type's defined values is also set in this value.
        /// </summary>
        public static ulong AllFlagsSetValue { get; }

        static FlagValueCache()
        {
            if (typeof(T).BaseType != typeof(Enum)) throw new Exception("The type parameter must be an enum type.");

            foreach (var value in (T[])Enum.GetValues(typeof(T)))
                AllFlagsSetValue |= GetNumericValue(value);
        }
    }
}

我们正在检查是否设置了至少一个标志是什么意思?

好吧,这个解决方案可能无法正确回答以下无意义的枚举:

[Flags]
public enum Nonsense
{
    One = 1,

    // Eh, why does this value need TWO bits when those bits are NOT defined as individual values?
    TwoAndFour = 2 | 4,
}

在这里,EnumHelper.HasAnyFlagBitSet((Nonsense)2)将 return true,这在技术上是不正确的,因为2它不是一个定义的标志。

但是,它对所有合理的标志枚举都非常有效,包括具有多标志的枚举:

[Flags]
public enum Fine
{
    One = 1,
    Two = 2,
    Four = 4,

    // Fine, and sensible, since these flags exist individually
    TwoAndFour = 2 | 4,
}
于 2021-10-07T15:31:02.993 回答
-2

对不起,但我会在 VB 中显示它:)

   <Flags()> Public Enum Cnt As Integer
        None = 0
        One = 1
        Two = 2
        Three = 4
        Four = 8    
    End Enum

    Sub Test()
    Dim CntValue As New Cnt
    CntValue += Cnt.One
    CntValue += Cnt.Three
    Console.WriteLine(CntValue)
    End Sub

CntValue = 5 所以枚举包含 1 + 4

于 2016-07-29T11:36:20.670 回答