Getting the max value of an enum

问题:

How do you get the max value of an enum?

回答1:

Enum.GetValues() seems to return the values in order, so you can do something like this:

// given this enum: public enum Foo {     Fizz = 3,      Bar = 1,     Bang = 2 }  // this gets Fizz var lastFoo = Enum.GetValues(typeof(Foo)).Cast<Foo>().Last(); 

Edit

For those not willing to read through the comments: You can also do it this way:

var lastFoo = Enum.GetValues(typeof(Foo)).Cast<Foo>().Max(); 

... which will work when some of your enum values are negative.

回答2:

I agree with Matt's answer. If you need just min and max int values, then you can do it as follows.

Maximum:

Enum.GetValues(typeof(Foo)).Cast<int>().Max(); 

Minimum:

Enum.GetValues(typeof(Foo)).Cast<int>().Min(); 

回答3:

According to Matt Hamilton's answer, I thought on creating an Extension method for it.

Since ValueType is not accepted as a generic type parameter constraint, I didn't find a better way to restrict T to Enum but the following.

Any ideas would be really appreciated.

PS. please ignore my VB implicitness, I love using VB in this way, that's the strength of VB and that's why I love VB.

Howeva, here it is:

C#:

static void Main(string[] args) {     MyEnum x = GetMaxValue<MyEnum>(); }  public static TEnum GetMaxValue<TEnum>()      where TEnum : IComparable, IConvertible, IFormattable {     Type type = typeof(TEnum);      if (!type.IsSubclassOf(typeof(Enum)))         throw new             InvalidCastException                 ("Cannot cast '" + type.FullName + "' to System.Enum.");      return (TEnum)Enum.ToObject(type, Enum.GetValues(type).Cast<int>().Last()); }  enum MyEnum {     ValueOne,     ValueTwo } 

VB:

Public Function GetMaxValue _     (Of TEnum As {IComparable, IConvertible, IFormattable})() As TEnum      Dim type = GetType(TEnum)      If Not type.IsSubclassOf(GetType([Enum])) Then _         Throw New InvalidCastException _             ("Cannot cast '" & type.FullName & "' to System.Enum.")      Return [Enum].ToObject(type, [Enum].GetValues(type) _                         .Cast(Of Integer).Last) End Function 

回答4:

This is slightly nitpicky but the actual maximum value of any enum is Int32.MaxValue (assuming it's a enum derived from int). It's perfectly legal to cast any Int32 value to an any enum regardless of whether or not it actually declared a member with that value.

Legal:

enum SomeEnum {     Fizz = 42 }  public static void SomeFunc() {     SomeEnum e = (SomeEnum)5; } 

回答5:

After tried another time, I got this extension method:

public static class EnumExtension {     public static int Max(this Enum enumType)     {                    return Enum.GetValues(enumType.GetType()).Cast<int>().Max();                  } }  class Program {     enum enum1 { one, two, second, third };     enum enum2 { s1 = 10, s2 = 8, s3, s4 };     enum enum3 { f1 = -1, f2 = 3, f3 = -3, f4 };      static void Main(string[] args)     {         Console.WriteLine(enum1.one.Max());             } } 

回答6:

Use the Last function could not get the max value. Use the "max" function could. Like:

 class Program     {         enum enum1 { one, two, second, third };         enum enum2 { s1 = 10, s2 = 8, s3, s4 };         enum enum3 { f1 = -1, f2 = 3, f3 = -3, f4 };          static void Main(string[] args)         {             TestMaxEnumValue(typeof(enum1));             TestMaxEnumValue(typeof(enum2));             TestMaxEnumValue(typeof(enum3));         }          static void TestMaxEnumValue(Type enumType)         {             Enum.GetValues(enumType).Cast<Int32>().ToList().ForEach(item =>                 Console.WriteLine(item.ToString()));              int maxValue = Enum.GetValues(enumType).Cast<int>().Max();                  Console.WriteLine("The max value of {0} is {1}", enumType.Name, maxValue);         }     } 

回答7:

There are methods for getting information about enumerated types under System.Enum.

So, in a VB.Net project in Visual Studio I can type "System.Enum." and the intellisense brings up all sorts of goodness.

One method in particular is System.Enum.GetValues(), which returns an array of the enumerated values. Once you've got the array, you should be able to do whatever is appropriate for your particular circumstances.

In my case, my enumerated values started at zero and skipped no numbers, so to get the max value for my enum I just need to know how many elements were in the array.

VB.Net code snippets:

'''''''  Enum MattType   zerothValue         = 0   firstValue          = 1   secondValue         = 2   thirdValue          = 3 End Enum  '''''''  Dim iMax      As Integer  iMax = System.Enum.GetValues(GetType(MattType)).GetUpperBound(0)  MessageBox.Show(iMax.ToString, "Max MattType Enum Value")  ''''''' 

回答8:

In agreement with Matthew J Sullivan, for C#:

   Enum.GetValues(typeof(MyEnum)).GetUpperBound(0); 

I'm really not sure why anyone would want to use:

   Enum.GetValues(typeof(MyEnum)).Cast<MyEnum>().Last(); 

...As word-for-word, semantically speaking, it doesn't seem to make as much sense? (always good to have different ways, but I don't see the benefit in the latter.)

回答9:

In F#, with a helper function to convert the enum to a sequence:

type Foo =     | Fizz  = 3     | Bang  = 2  // Helper function to convert enum to a sequence. This is also useful for iterating. // stackoverflow.com/questions/972307/can-you-loop-through-all-enum-values-c let ToSeq (a : 'A when 'A : enum<'B>) =     Enum.GetValues(typeof<'A>).Cast<'B>()  // Get the max of Foo let FooMax = ToSeq (Foo()) |> Seq.max    

 > type Foo = | Fizz = 3 | Bang = 2 > val ToSeq : 'A -> seq<'B> when 'A : enum<'B> > val FooMax : Foo = Fizz 

The "when 'A : enum<'B>" is not required by the compiler for the definition, but is required for any use of ToSeq, even by a valid enum type.

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