为了说明,我们来看一个简单的控制台应用程序,并在其中创建两个枚举：汽车和动物：
public enum Cars
{
Honda = 0,Toyota = 1,Chevrolet = 2
}
public enum Animals
{
Dog = 0,Cat = 1,Tiger = 2
}
并在主要方法中做到这一点：
public static void Main()
{
List<Cars> cars = new List<Cars>();
List<Animals> animals = new List<Animals>();
cars.Add(Cars.Chevrolet);
cars.Add(Cars.Honda);
cars.Add(Cars.Toyota);
foreach (Animals isItACar in cars)
{
Console.WriteLine(isItACar.ToString());
}
Console.ReadLine();
}
它将在控制台中打印：
06002
为什么会这样呢？我的第一个猜测是,枚举实际上并不是一个类型,它只是和int,但这不是真的：如果我们写：
Console.WriteLine(Animals.Tiger.GetType()全名.);
我们会得到他的完全合格的名字打印！那为什么这样呢？
解决方法
让我们重写一下你的循环：
public static void Main()
{
List<Cars> cars = new List<Cars>();
List<Animals> animals = new List<Animals>();
cars.Add(Cars.Chevrolet);
cars.Add(Cars.Honda);
cars.Add(Cars.Toyota);
foreach (Cars value in cars)
{
// This time the cast is explicit.
Animals isItACar = (Animals) value;
Console.WriteLine(isItACar.ToString());
}
Console.ReadLine();
}
现在这个结果让你感到惊讶吗？希望不是,除了可以从一个枚举到另一个枚举的事实.这只是您原始代码正在做的更为明确的版本.
事实上,每个foreach循环中都有一个隐式的转换(尽管通常是一个no-op)是大多数开发人员会发现混乱的一点,我认为.
从C#3.0规范的8.8.4节：
The above steps,if successful,
unambiguously produce a collection
type C,enumerator type E and element
type T. A foreach statement of the
form
foreach (V v in x) embedded-statement
is then expanded to:
{
E e = ((C)(x)).GetEnumerator();
try {
V v;
while (e.MoveNext()) {
v = (V)(T)e.Current;
embedded-statement
}
}
finally {
... // Dispose e
}
}
枚举转换本身包含在6.2.2节中：
The explicit enumeration conversions
are:
>从sbyte,byte,short,ushort,int,uint,long,ulong,char,float,double或decimal到任何枚举类型.
>从任何枚举类型到sbyte,double或decimal.
>从任何枚举类型到任何其他枚举类型.
An explicit enumeration conversion between two types is processed by treating any participating enum-type as the underlying type of that enum-type,and then performing an implicit or explicit numeric conversion between the resulting types. For example,given an enum-type E with and underlying type of int,a conversion from E to byte is processed as an explicit numeric conversion (§6.2.1) from int to byte,and a conversion from byte to E is processed as an implicit numeric conversion (§6.1.2) from byte to int.
