扩展方法为空的枚举

问题描述：

我想写为空的一个枚举的扩展方法的。照片就像这个例子：

I'm trying to write an Extension method for nullable Enums.
Like with this example:

// ItemType is an enum
ItemType? item;
...

item.GetDescription();

所以我写了这个方法，它不会编译由于某种原因，我不明白：

So I wrote this method which doesn't compile for some reason that I don't understand:

public static string GetDescription(this Enum? theEnum)
{
    if (theEnum == null)
        return string.Empty;

    return GetDescriptionAttribute(theEnum);
}

我收到以下错误枚举：

唯一的非空值类型可能是潜在的system.nullable

only non-nullable value type could be underlying of system.nullable

为什么呢？枚举不能有值空！

Why? Enum can not have the value null!

更新：

如果有很多枚举，的ItemType 是其中之一的只是一个例子。的

If have lots of enums, ItemType is just an example of one of them.

答

System.Enum 是类，所以刚落？这应该工作。

System.Enum is a class, so just drop the ? and this should work.

（以这应该工作，我的意思是，如果你传递了一个空值的ItemType？，你会得到一个空 枚举$ C $的方法C>）

(By "this should work", I mean if you pass in a null-valued ItemType?, you'll get a null Enum in the method.)

public static string GetDescription(this Enum theEnum)
{
    if (theEnum == null)
        return string.Empty;
    return GetDescriptionAttribute(theEnum);
}
enum Test { blah }

Test? q = null;
q.GetDescription(); // => theEnum parameter is null
q = Test.blah;
q.GetDescription(); // => theEnum parameter is Test.blah

扩展方法为空​​的枚举

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扩展方法为空的枚举