假设我有这样一个enum:
[Flags]
enum Letters
{
A = 1,
B = 2,
C = 4,
AB = A | B,
All = A | B | C,
}
为了检查AB是否被设置，我可以这样做:
if((letter & Letters.AB) == Letters.AB)
有没有一种比下面更简单的方法来检查是否设置了一个组合标志常量的任何标志?
if((letter & Letters.A) == Letters.A || (letter & Letters.B) == Letters.B)
例如，可以将&与其他东西交换吗?
当前回答
我们能否轻松有效地找出是否至少设置了一个标志?
好吧，如果您对检查是否至少设置了一个标志位感到满意，那么是的!
用法:
if (EnumHelper.HasAnyFlagBitsSet(letter))
实现:
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);
}
}
}
我们检查是否至少设置了一个标志位，这意味着什么?
好吧，这个解决方案可能无法正确回答以下这些无意义的枚举:
[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,
}
这里，EnumHelper.HasAnyFlagBitSet((无意义)2)将返回true，这在技术上是不正确的，因为2不是一个定义的标志。
然而，对于所有敏感的标志枚举，包括带有多个标志的枚举，它工作得非常好:
[Flags]
public enum Fine
{
One = 1,
Two = 2,
Four = 4,
// Fine, and sensible, since these flags exist individually
TwoAndFour = 2 | 4,
}
其他回答
我使用扩展方法来写这样的东西:
if (letter.IsFlagSet(Letter.AB))
...
代码如下:
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;
}
}
我创建了一个简单的扩展方法，不需要检查Enum类型:
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。标准的HasFlag方法没有，所以我创建了一个扩展来覆盖它。
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));
}
享受吧!
我们能否轻松有效地找出是否至少设置了一个标志?
好吧，如果您对检查是否至少设置了一个标志位感到满意，那么是的!
用法:
if (EnumHelper.HasAnyFlagBitsSet(letter))
实现:
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);
}
}
}
我们检查是否至少设置了一个标志位，这意味着什么?
好吧，这个解决方案可能无法正确回答以下这些无意义的枚举:
[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,
}
这里，EnumHelper.HasAnyFlagBitSet((无意义)2)将返回true，这在技术上是不正确的，因为2不是一个定义的标志。
然而，对于所有敏感的标志枚举，包括带有多个标志的枚举，它工作得非常好:
[Flags]
public enum Fine
{
One = 1,
Two = 2,
Four = 4,
// Fine, and sensible, since these flags exist individually
TwoAndFour = 2 | 4,
}
你可以在enum上使用这个扩展方法，用于任何类型的enum:
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;
}
如果你想知道字母AB中是否有字母，你必须使用AND &运算符。喜欢的东西:
if ((letter & Letters.AB) != 0)
{
// Some flag (A,B or both) is enabled
}
else
{
// None of them are enabled
}
