将值解析为可为空的枚举 [英] Parsing value into nullable enumeration

问题描述

比方说我有这个:

PriorityType? priority;
string userInput = ...;

我无法更改其定义方式: PriorityType?优先级，因为它实际上是与另一段代码的合同的一部分.

I cannot change how this is defined: PriorityType? priority because it's actually part of a contract with another piece of code.

我尝试过此方法，但是它不起作用:

I tried this, but it does not work:

if (Enum.TryParse<PriorityType?>(userInput, out priority)) {

正确的方法是什么?

推荐答案

最简单的方法:

PriorityType tempPriority;
PriorityType? priority;

if (Enum.TryParse<PriorityType>(userInput, out tempPriority))
    priority = tempPriority;

这是我能想到的最好的方法

This is the best I can come up with:

public static class NullableEnum
{
    public static bool TryParse<T>(string value, out T? result) where T :struct, IConvertible
    {
        if (!typeof(T).IsEnum)
            throw new Exception("This method is only for Enums");

        T tempResult = default(T);

        if (Enum.TryParse<T>(value, out tempResult))
        {
            result = tempResult;
            return true;
        }

        result = null;
        return false;
    }
}

使用:

if (NullableEnum.TryParse<PriorityType>(userInput, out priority))

上面的类可以像 Enum.TryParse 一样使用，除了输入可以为空.您可以添加另一个采用不可为空的 T 的重载函数，以便您可以根据需要在两个实例中使用它.不幸的是，扩展方法在枚举类型上不能很好地工作(据我所知，我可以在很短的时间内尝试对其进行操作).

The above class can be used just like Enum.TryParse except with a nullable input. You could add another overloaded function that takes a non-nullable T so that you could use it in both instances if you want. Unfortunately extension methods don't work very well on enum types (as far as I could try to manipulate it in the short time I tried).

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