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

如果你觉得很烦,你可以这样写一个函数:

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))
{
   // ...
}

其他回答

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
}

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!

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);   
   }
}

使用实例显示如下信息:

//       1 of 3 families in the sample have no pets. 
//       2 of 3 families in the sample have a dog.

如果可以使用。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

一样

letter.HasFlag(Letters.AB)

从。net 4开始,你可以使用一个简写版本,无需显式指定&:

if(Letters.AB.HasFlag(Letters.C))