能够通过反射分配无效的Enum值

Question

I've just come across some strange behavior when setting an enum's value via reflection. It seems like I'm able to set an invalid value for the enum:

class EnumReflector
{
    public enum MyEnum
    {
        Option1 = 0,
        Option2,
        Option3
    }

    public MyEnum TheEnum { get; set; }

    public void Test()
    {
        PropertyInfo pi = this.GetType().GetProperty("TheEnum");
        string badValue = "1234";
        object propertyValue = Enum.Parse(pi.PropertyType, badValue, true);

        pi.SetValue(this, propertyValue, null);
    }
}

Now, if I call this:

        EnumReflector e = new EnumReflector();
        e.Test();
        if (e.TheEnum == EnumReflector.MyEnum.Option1 ||
            e.TheEnum == EnumReflector.MyEnum.Option2 ||
            e.TheEnum == EnumReflector.MyEnum.Option3)
        {
            Console.WriteLine("Value is valid");
        }
        else
        {
            Console.WriteLine("Value is invalid: {0} ({1})", e.TheEnum.ToString(), (int)e.TheEnum);
        }

The output is:

Value is invalid: 1234 (1234)

How can this be? I though one of the very natures of enums is their restricted value-set!

Answer 1

Enums are just integers (of any integer primitive type, which can be specified) with some defined named constants. There is no need for reflection to assign a value which has no named constant:

enum MyEnum {
    None, One, Two
}

MyEnum e = (MyEnum)100;

Compiles and works just fine. Note that this is also the reason for the Enum.IsDefined() static method, which checks if an enum value is a defined value.

Answer 2

Enums are really stricted value-set, but at the compile time. Here is the disadvantage of the reflection: you loose all the compile-time checks, provided by the compiler and operate the values for own responsibility.

Answer 3

You don't even need to resort to reflection:

EnumReflector e = new EnumReflector();

e.TheEnum = (EnumReflector.MyEnum)1234;

if (e.TheEnum == EnumReflector.MyEnum.Option1 ||
    e.TheEnum == EnumReflector.MyEnum.Option2 ||
    e.TheEnum == EnumReflector.MyEnum.Option3)
{
    Console.WriteLine("Value is valid");
}
else
{
    Console.WriteLine("Value is invalid: {0} ({1})",
                      e.TheEnum.ToString(), (int)e.TheEnum);
}