我更喜欢使用可为null的枚举类型变量。

var enumValue = (MyEnum?)enumInt;

if (!enumValue.HasValue)
{
    throw new ArgumentException(nameof(enumValue));
}

你应该建立一些类型匹配的放松机制，以更加健壮。

public static T ToEnum<T>(dynamic value)
{
    if (value == null)
    {
        // default value of an enum is the object that corresponds to
        // the default value of its underlying type
        // https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/default-values-table
        value = Activator.CreateInstance(Enum.GetUnderlyingType(typeof(T)));
    }
    else if (value is string name)
    {
        return (T)Enum.Parse(typeof(T), name);
    }

    return (T)Enum.ToObject(typeof(T),
             Convert.ChangeType(value, Enum.GetUnderlyingType(typeof(T))));
}

测试用例

[Flags]
public enum A : uint
{
    None  = 0, 
    X     = 1 < 0,
    Y     = 1 < 1
}

static void Main(string[] args)
{
    var value = EnumHelper.ToEnum<A>(7m);
    var x = value.HasFlag(A.X); // true
    var y = value.HasFlag(A.Y); // true

    var value2 = EnumHelper.ToEnum<A>("X");

    var value3 = EnumHelper.ToEnum<A>(null);

    Console.ReadKey();
}

您只需使用显式转换Cast int to enum或enum to int

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine((int)Number.three); //Output=3

        Console.WriteLine((Number)3);// Outout three
        Console.Read();
    }

    public enum Number
    {
        Zero = 0,
        One = 1,
        Two = 2,
        three = 3
    }
}

只要投它：

MyEnum e = (MyEnum)3;

使用Enum.IsDefined检查它是否在范围内：

if (Enum.IsDefined(typeof(MyEnum), 3)) { ... }

这是一个标志枚举感知安全转换方法：

public static bool TryConvertToEnum<T>(this int instance, out T result)
  where T: Enum
{
  var enumType = typeof (T);
  var success = Enum.IsDefined(enumType, instance);
  if (success)
  {
    result = (T)Enum.ToObject(enumType, instance);
  }
  else
  {
    result = default(T);
  }
  return success;
}

以以下示例为例：

int one = 1;
MyEnum e = (MyEnum)one;