C# 如何尝试解析枚举值？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1082532/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to TryParse for Enum value?
提问by Manish Basantani
I want to write a function which can validate a given value (passed as a string) against possible values of an enum. In the case of a match, it should return the enum instance; otherwise, it should return a default value.
我想编写一个函数来验证给定值（作为字符串传递）针对enum. 在匹配的情况下，它应该返回枚举实例；否则，它应该返回一个默认值。
The function may not internally use try/catch, which excludes using Enum.Parse, which throws an exception when given an invalid argument.
该函数可能不会在内部使用try/ catch，这不包括 using Enum.Parse，当给定无效参数时会引发异常。
I'd like to use something along the lines of a TryParsefunction to implement this:
我想使用类似于TryParse函数的东西来实现这一点：
public static TEnum ToEnum<TEnum>(this string strEnumValue, TEnum defaultValue)
{
object enumValue;
if (!TryParse (typeof (TEnum), strEnumValue, out enumValue))
{
return defaultValue;
}
return (TEnum) enumValue;
}
采纳答案by Victor Arndt Mueller
As others have said, you have to implement your own TryParse. Simon Mourier is providing a full implementation which takes care of everything.
正如其他人所说，您必须实现自己的TryParse. Simon Mourier 提供了一个完整的实现，它可以处理一切。
If you are using bitfield enums (i.e. flags), you also have to handle a string like "MyEnum.Val1|MyEnum.Val2"which is a combination of two enum values. If you just call Enum.IsDefinedwith this string, it will return false, even though Enum.Parsehandles it correctly.
如果您使用位域枚举（即标志），您还必须处理一个字符串，例如"MyEnum.Val1|MyEnum.Val2"它是两个枚举值的组合。如果你只是Enum.IsDefined用这个字符串调用，它会返回 false，即使Enum.Parse正确处理它。
Update
更新
As mentioned by Lisa and Christian in the comments, Enum.TryParseis now available for C# in .NET4 and up.
MSDN Docs
正如 Lisa 和 Christian 在评论中提到的，Enum.TryParse现在可用于 .NET4 及更高版本的 C#。
MSDN 文档
回答by Spence
Have a look at the Enum class (struct ? ) itself. There is a Parse method on that but I'm not sure about a tryparse.
看看 Enum 类 (struct ? ) 本身。有一个 Parse 方法，但我不确定 tryparse。
回答by Philippe Leybaert
The only way to avoid exception handling is to use the GetNames() method, and we all know that exceptions shouldn't be abused for common application logic :)
避免异常处理的唯一方法是使用 GetNames() 方法，我们都知道异常不应被滥用于常见的应用程序逻辑:)
回答by Ahmad Mageed
There's currently no out of the box Enum.TryParse. This has been requested on Connect (Still no Enum.TryParse) and got a response indicating possible inclusion in the next framework after .NET 3.5. You'll have to implement the suggested workarounds for now.
目前没有开箱即用的 Enum.TryParse。这已在 Connect 上被请求（仍然没有 Enum.TryParse），并得到了一个响应，表明可能包含在 .NET 3.5 之后的下一个框架中。您现在必须实施建议的解决方法。
回答by Nader Shirazie
Is caching a dynamically generated function/dictionary permissable?
缓存动态生成的函数/字典是否允许？
Because you don't (appear to) know the type of the enum ahead of time, the first execution could generate something subsequent executions could take advantage of.
因为您不（似乎）提前知道枚举的类型，所以第一次执行可能会产生一些后续执行可以利用的东西。
You could even cache the result of Enum.GetNames()
你甚至可以缓存 Enum.GetNames() 的结果
Are you trying to optimize for CPU or Memory? Do you reallyneed to?
您是否正在尝试针对 CPU 或内存进行优化？你真的需要吗？
回答by Richard
In the end you have to implement this around Enum.GetNames:
最后，您必须在以下方面实施Enum.GetNames：
public bool TryParseEnum<T>(string str, bool caseSensitive, out T value) where T : struct {
// Can't make this a type constraint...
if (!typeof(T).IsEnum) {
throw new ArgumentException("Type parameter must be an enum");
}
var names = Enum.GetNames(typeof(T));
value = (Enum.GetValues(typeof(T)) as T[])[0]; // For want of a better default
foreach (var name in names) {
if (String.Equals(name, str, caseSensitive ? StringComparison.Ordinal : StringComparison.OrdinalIgnoreCase)) {
value = (T)Enum.Parse(typeof(T), name);
return true;
}
}
return false;
}
Additional notes:
补充说明：
Enum.TryParseis included in .NET 4. See here http://msdn.microsoft.com/library/dd991876(VS.100).aspx- Another approach would be to directly wrap
Enum.Parsecatching the exception thrown when it fails. This could be faster when a match is found, but will likely to slower if not. Depending on the data you are processing this may or may not be a net improvement.
Enum.TryParse包含在 .NET 4 中。请参见此处http://msdn.microsoft.com/library/dd991876(VS.100).aspx- 另一种方法是直接包装
Enum.Parse捕获失败时抛出的异常。当找到匹配时，这可能会更快，但如果没有，则可能会更慢。根据您正在处理的数据，这可能是也可能不是净改进。
EDIT: Just seen a better implementation on this, which caches the necessary information: http://damieng.com/blog/2010/10/17/enums-better-syntax-improved-performance-and-tryparse-in-net-3-5
编辑：刚刚看到了一个更好的实现，它缓存了必要的信息：http: //damieng.com/blog/2010/10/17/enums-better-syntax-improved-performance-and-tryparse-in-net- 3-5
回答by Thorarin
Enum.IsDefined will get things done. It may not be as efficient as a TryParse would probably be, but it will work without exception handling.
Enum.IsDefined 将完成任务。它可能不如 TryParse 有效，但它可以在没有异常处理的情况下工作。
public static TEnum ToEnum<TEnum>(this string strEnumValue, TEnum defaultValue)
{
if (!Enum.IsDefined(typeof(TEnum), strEnumValue))
return defaultValue;
return (TEnum)Enum.Parse(typeof(TEnum), strEnumValue);
}
Worth noting: a TryParsemethod was added in .NET 4.0.
值得注意的是：TryParse.NET 4.0 中添加了一个方法。
回答by Victor Arndt Mueller
As others already said, if you don't use Try&Catch, you need to use IsDefined or GetNames... Here are some samples...they basically are all the same, the first one handling nullable enums. I prefer the 2nd one as it's an extension on strings, not enums...but you can mix them as you want!
正如其他人已经说过的，如果您不使用 Try&Catch，则需要使用 IsDefined 或 GetNames...这里有一些示例...它们基本上都是相同的，第一个处理可为空的枚举。我更喜欢第二个，因为它是字符串的扩展，而不是枚举……但是您可以根据需要混合使用它们！
- www.objectreference.net/post/Enum-TryParse-Extension-Method.aspx
- flatlinerdoa.spaces.live.com/blog/cns!17124D03A9A052B0!605.entry
- mironabramson.com/blog/post/2008/03/Another-version-for-the-missing-method-EnumTryParse.aspx
- lazyloading.blogspot.com/2008/04/enumtryparse-with-net-35-extension.html
- www.objectreference.net/post/Enum-TryParse-Extension-Method.aspx
- flatlinerdoa.spaces.live.com/blog/cns!17124D03A9A052B0!605.entry
- mironabramson.com/blog/post/2008/03/Another-version-for-the-missing-method-EnumTryParse.aspx
- lazyloading.blogspot.com/2008/04/enumtryparse-with-net-35-extension.html
回答by Jon Skeet
I have an optimised implementation you could use in UnconstrainedMelody. Effectively it's just caching the list of names, but it's doing so in a nice, strongly typed, generically constrained way :)
我有一个优化的实现，你可以在UnconstrainedMelody 中使用。实际上，它只是缓存名称列表，但它是以一种很好的、强类型的、通用约束的方式来做的:)
回答by Naveed Ahmed
This method will convert a type of enum:
此方法将转换枚举类型：
public static TEnum ToEnum<TEnum>(object EnumValue, TEnum defaultValue)
{
if (!Enum.IsDefined(typeof(TEnum), EnumValue))
{
Type enumType = Enum.GetUnderlyingType(typeof(TEnum));
if ( EnumValue.GetType() == enumType )
{
string name = Enum.GetName(typeof(HLink.ViewModels.ClaimHeaderViewModel.ClaimStatus), EnumValue);
if( name != null)
return (TEnum)Enum.Parse(typeof(TEnum), name);
return defaultValue;
}
}
return (TEnum)Enum.Parse(typeof(TEnum), EnumValue.ToString());
}
It checks the underlying type and get the name against it to parse. If everything fails it will return default value.
它检查底层类型并根据它获取名称以进行解析。如果一切都失败，它将返回默认值。
