Parse string to enum type

问题:

I have an enum type like this as an example:

public Enum MyEnum {
    enum1, enum2, enum3 };

I'll read a string from config file. What I need it to parse the string to MyEnum type or null o not defined. Not sure if the following codes will work (sorry for not having access to my VS right now):

// example: ParseEnum<MyEnum>("ENUM1", ref eVal);
bool ParseEnum<T>(string value1, ref eVal) where T : Enum
{
  bool bRet = false;
  var x = from x in Enum.GetNames(typeof(T)) where 
       string.Equals(value1, x, StringComparison. OrdinalIgnoreCase)
       select x;
  if (x.Count() == 1 )
  {
    eVal = Enum.Parse(typeof(T), x.Item(0)) as T;
    bRet = true;
  }
  return bRet;
}

Not sure if it is correct or there is any other simple way to parse a string to MyEnum value?

回答1:

What about something like:

public static class EnumUtils
{
    public static Nullable<T> Parse<T>(string input) where T : struct
    {
        //since we cant do a generic type constraint
        if (!typeof(T).IsEnum)
        {
            throw new ArgumentException("Generic Type 'T' must be an Enum");
        }
        if (!string.IsNullOrEmpty(input))
        {
            if (Enum.GetNames(typeof(T)).Any(
                  e => e.Trim().ToUpperInvariant() == input.Trim().ToUpperInvariant()))
            {
                return (T)Enum.Parse(typeof(T), input, true);
            }
        }
        return null;
    }
}

Used as:

MyEnum? value = EnumUtils.Parse<MyEnum>("foo");

(Note: old version used try/catch around Enum.Parse)

回答2:

private enum MyEnum
{
    Enum1 = 1, Enum2 = 2, Enum3 = 3, Enum4 = 4, Enum5 = 5, Enum6 = 6, 
    Enum7 = 7, Enum8 = 8, Enum9 = 9, Enum10 = 10
}

private static Object ParseEnum<T>(string s)
{
    try
    {
        var o = Enum.Parse(typeof (T), s);
        return (T)o;
    }
    catch(ArgumentException)
    {
        return null;
    }
}

static void Main(string[] args)
{
   Console.WriteLine(ParseEnum<MyEnum>("Enum11"));
   Console.WriteLine(ParseEnum<MyEnum>("Enum1"));
   Console.WriteLine(ParseEnum<MyEnum>("Enum6").GetType());
   Console.WriteLine(ParseEnum<MyEnum>("Enum10"));
}

OUTPUT:

    //This line is empty as Enum11 is not there and function returns a null
Enum1
TestApp.Program+MyEnum
Enum10
Press any key to continue . . .

回答3:

This is an old question, but now .NET 4.5 has Enum.TryParse().

http://msdn.microsoft.com/en-us/library/dd991317.aspx

回答4:

I have a TryParseName method in UnconstrainedMelody, a library for delegate and enum utility methods which uses "inexpressible" constraints via some postbuild trickery. (Code using the library doesn't need a postbuild, just to be clear.)

You would use it like this:

Foo foo;
bool parsed = Enums.TryParseName<Foo>(name, out foo);

I don't currently have a case-insensitive version, but I could easily introduce one if you wanted. Note that this doesn't try to parse numbers e.g. "12" like the built-in version does, nor does it try to parse comma-separated lists of flags. I may add the flags version later on, but I can't see much point in the numeric version.

This is done without boxing and without execution time type checking. Having the constraint is really handy :)

Please let me know if you'd find a case-insensitive parse useful...

回答5:

I have just combined the syntax from here, with the exception handling from here, to create this:

public static class Enum<T>
{
    public static T Parse(string value)
    {
        //Null check
        if(value == null) throw new ArgumentNullException("value");
        //Empty string check
        value = value.Trim();
        if(value.Length == 0) throw new ArgumentException("Must specify valid information for parsing in the string", "value");
        //Not enum check
        Type t = typeof(T);
        if(!t.IsEnum) throw new ArgumentException("Type provided must be an Enum", "TEnum");

        return (T)Enum.Parse(typeof(T), value);
    }
}

You could twiddle it a bit to return null instead of throwing exceptions.

回答6:

If you're using .NET 3.5 (or even 2.0, if you trim out the extension method), I've had great luck with the techniques in this article:

Enumerations and Strings - Stop the Madness!

EDIT: Domain is gone and is now a link farm. I pulled the code (slightly modified and added to over time) from our codebase at work, which you can now find here:

https://gist.github.com/1305566

回答7:

You can use TryParse if you want to avoid using try/catch.

MyEnum eVal;
if (Enum.TryParse("ENUM2", true, out eVal)){
    // now eVal is the enumeration element: enum2 
}
//unable to parse. You can log the error, exit, redirect, etc...

I modified the selected answer a little bit. I hope you like it.

public static class EnumUtils
{
    public static Nullable<T> Parse<T>(string input) where T : struct
    {
        //since we cant do a generic type constraint
        if (!typeof(T).IsEnum)
        {
            throw new ArgumentException("Generic Type 'T' must be an Enum");
        }

        int intVal;
        if (!string.IsNullOrEmpty(input) && !int.TryParse(input, out intVal))
        {
            T eVal;
            if (Enum.TryParse(input, true, out eVal))
            {
                return eVal;
            }
        }
        return null;
    }
}

回答8:

To return Enum by string, if contains:

    public static T GetEnum<T>(string s)
    {
        Array arr = Enum.GetValues(typeof(T));
        foreach (var x in arr)
        {
            if (x.ToString().Contains(s))
                return (T)x;
        }
        return default(T);
    }