严格将字符串解析为枚举的最佳方法是什么？

Question

Let's say I have an enum:

public enum MyEnum
{
    OptionOne = 0,
    OptionTwo = 2,
    OptionThree = 4
}

Like it was said in the How should I convert a string to an enum in C#? question, I parse enum from string, using Enum.Parse method:

public class Enumer
{
    public static MyEnum? ParseEnum(string input)
    {
        try
        {
            return (MyEnum) Enum.Parse(typeof (MyEnum), input);
        }
        catch (ArgumentException)
        {
            return null;
        }
    }

}

Unfortunately, it doesn't work as expected with integer numbers, represented as strings.
I do not expect Parse.Enum() to convert int from string, but actually it does.
A simple test:

[TestClass]
public class Tester
{
    [TestMethod]
    public void TestEnum()
    {
        Assert.AreEqual(MyEnum.OptionTwo, Enumer.ParseEnum("OptionTwo"));
        Assert.IsNull(Enumer.ParseEnum("WrongString"));
        Assert.IsNull(Enumer.ParseEnum("2")); // returns 2 instead of null
        Assert.IsNull(Enumer.ParseEnum("12345")); // returns 12345 instead of null
    }
}

Only two checks of four can be passed.
Enumer.ParseEnum("2") returns MyEnum.OptionTwo instead of null .
Moreover, Enumer.ParseEnum("12345") returns 12345, regardless it's out of the scope.

What is the best way to parse:

1. Only string values of "MyEnum.OptionOne", "MyEnum.OptionTwo", "MyEnum.OptionThree" into their enum counterparts.
2. Strings "MyEnum.OptionOne", "MyEnum.OptionTwo", "MyEnum.OptionThree" AND the values of 0, 2 and 4 into MyEnum.OptionOne, MyEnum.OptionTwo, MyEnum.OptionThree respectively?

The link to the similar question How should I convert a string to an enum in C#? doesn't help with the test provided - it still converts strings as integers, even when they are out of the enum scope.

Answer 1

You can do this yourself using Enum.GetValues(Type enumType) .

public static MyEnum? ParseEnum(string input)
{
    return (MyEnum?) Enum.GetValues(typeof(MyEnum)).OfType<object>()
                         .FirstOrDefault(v => v.ToString() == input);
}

Adding support for integers you can also add.

public static MyEnum? ParseEnum(string input)
{
    int value;
    var isInt = int.TryParse(input, out value);
    return (MyEnum?) Enum.GetValues(typeof(MyEnum)).OfType<object>()
                         .FirstOrDefault(v => v.ToString() == input
                                           || (isInt & (int)v == value));
}

Since I am not 100% sure about your last requirements I add one that includes the name as well and is more generic

public static T? ParseEnum<T>(string input)
    where T : struct 
{
    int value;
    var isInt = int.TryParse(input, out value);
    return (T?)Enum.GetValues(typeof(T)).OfType<object>()
                   .FirstOrDefault(v => v.ToString() == typeof(T).Name + input
                                    || (isInt & (int)v == value));
}