C# 将 int 类型的对象强制转换为可为空的枚举 [英] C# cast object of type int to nullable enum

问题描述

我只需要能够将对象转换为可为空的枚举.对象可以是 enum、null 或 int.谢谢！

I just need to be able to cast an object to nullable enum. Object can be enum, null, or int. Thanks!

public enum MyEnum { A, B }
void Put(object value)
{
    System.Nullable<Myenum> val = (System.Nullable<MyEnum>)value;
}

Put(null);     // works
Put(Myenum.B); // works
Put(1);        // Invalid cast exception!!

推荐答案

怎么样:

MyEnum? val = value == null ? (MyEnum?) null : (MyEnum) value;

从装箱的 int 到 MyEnum 的转换(如果 value 为非空)，然后使用从 MyEnum 的隐式转换 到 Nullable.

The cast from boxed int to MyEnum (if value is non-null) and then use the implicit conversion from MyEnum to Nullable<MyEnum>.

没关系，因为您可以从枚举的装箱形式拆箱到其底层类型，反之亦然.

That's okay, because you're allowed to unbox from the boxed form of an enum to its underlying type, or vice versa.

我相信这实际上是一种转换，不保证 C# 规范可以正常工作，但 保证 CLI 规范可以正常工作.所以只要你在 CLI 实现上运行你的 C# 代码(你将是 :)，你会没事的.

I believe this is actually a conversion which isn't guaranteed to work by the C# spec, but is guaranteed to work by the CLI spec. So as long as you're running your C# code on a CLI implementation (which you will be :) you'll be fine.

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