从int：

YourEnum foo = (YourEnum)yourInt;

从字符串：

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for 
// enumerations marked with a [Flags] attribute.
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException(
        $"{yourString} is not an underlying value of the YourEnum enumeration."
    );
}

从一个数字：

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum), yourInt);

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;
}

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();
}

在C#中将int转换为enum的简单明了的方法：

public class Program
{
    public enum Color : int
    {
        Blue   = 0,
        Black  = 1,
        Green  = 2,
        Gray   = 3,
        Yellow = 4
    }

    public static void Main(string[] args)
    {
        // From string
        Console.WriteLine((Color) Enum.Parse(typeof(Color), "Green"));

        // From int
        Console.WriteLine((Color)2);

        // From number you can also
        Console.WriteLine((Color)Enum.ToObject(typeof(Color), 2));
    }
}

以以下示例为例：

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

对于数值，这是更安全的，因为无论发生什么情况，它都会返回一个对象：

public static class EnumEx
{
    static public bool TryConvert<T>(int value, out T result)
    {
        result = default(T);
        bool success = Enum.IsDefined(typeof(T), value);
        if (success)
        {
            result = (T)Enum.ToObject(typeof(T), value);
        }
        return success;
    }
}