Converting Null to Nullable Enum (Generic)

Question

I'm writing some Enum functionality, and have the following:

public static T ConvertStringToEnumValue<T>(string valueToConvert, 
    bool isCaseSensitive)
{
    if (String.IsNullOrWhiteSpace(valueToConvert))
        return (T)typeof(T).TypeInitializer.Invoke(null);

    valueToConvert = valueToConvert.Replace(" ", "");
    if (typeof(T).BaseType.FullName != "System.Enum" &&
        typeof(T).BaseType.FullName != "System.ValueType")
    {
        throw new ArgumentException("Type must be of Enum and not " +
            typeof (T).BaseType.FullName);
    }

    if (typeof(T).BaseType.FullName == "System.ValueType")
    {
        return (T)Enum.Parse(Nullable.GetUnderlyingType(typeof(T)),
            valueToConvert, !isCaseSensitive);
    }

    return (T)Enum.Parse(typeof(T), valueToConvert, !isCaseSensitive);
}

I now call this with the following:

EnumHelper.ConvertStringToEnumValue<Enums.Animals?>("Cat");

This works as expected. However, if I run this:

EnumHelper.ConvertStringToEnumValue<Enums.Animals?>(null);

it breaks with the error that the TypeInitializer is null.

Does anyone know how to solve this?

Thanks all!

Why on earth are you invoking the type initializer?? In my 9 years of C#, I have never needed to do that! — leppie
– leppie, Commented Sep 28, 2010 at 8:37
In fact that type initializer does not even return anything. The code is bogus, sorry. — leppie
– leppie, Commented Sep 28, 2010 at 8:38
@leppie, hence my posting of the question. I am looking for a way to do the above, and clearly the TypeInitializer isn't the correct way of doing this. The below answer from Preet is what I was looking for. — Richard
– Richard, Commented Sep 28, 2010 at 8:51
@leppie: he's asking a question to find a better way. Isn't that what SO is all about? Why so admonishing? — Kent Boogaart
– Kent Boogaart, Commented Sep 28, 2010 at 9:12
May i suggest you read up on the Type API. You should avoid using string comparison on types. For instance, typeof(T).BaseType.FullName != "System.Enum" may be better written as !typeof(T).IsEnum. Also typeof(T).BaseType.FullName != "System.ValueType" may be better written as !typeof(T).IsValueType. — Bear Monkey
– Bear Monkey, Commented Sep 28, 2010 at 9:23

Preet Sangha · Accepted Answer · 2010-09-28 08:35:43Z

10

try

if (String.IsNullOrWhiteSpace(valueToConvert))
              return default(T);

answered Sep 28, 2010 at 8:35

Preet Sangha

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Comments

diegodsp · Accepted Answer · 2016-04-10 13:19:02Z

1

I have an different approach, using extension and generics.

public static T ToEnum<T>(this string s) {
    if (string.IsNullOrWhiteSpace(s))
        return default(T);

    s = s.Replace(" ", "");
    if (typeof(T).BaseType.FullName != "System.Enum" &&
        typeof(T).BaseType.FullName != "System.ValueType") {
        throw new ArgumentException("Type must be of Enum and not " + typeof(T).BaseType.FullName);
    }

    if (typeof(T).BaseType.FullName == "System.ValueType")
        return (T)Enum.Parse(Nullable.GetUnderlyingType(typeof(T)), s, true);

    return (T)Enum.Parse(typeof(T), s, true);
}

Use like this...

Gender? g = "Female".ToEnum<Gender?>();

answered Apr 10, 2016 at 13:19

diegodsp

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Comments

Pangamma · Accepted Answer · 2018-01-19 18:36:31Z

This one gets the job done and it also looks pretty. Hope it helps!

    /// <summary>
    /// <para>More convenient than using T.TryParse(string, out T). 
    /// Works with primitive types, structs, and enums.
    /// Tries to parse the string to an instance of the type specified.
    /// If the input cannot be parsed, null will be returned.
    /// </para>
    /// <para>
    /// If the value of the caller is null, null will be returned.
    /// So if you have "string s = null;" and then you try "s.ToNullable...",
    /// null will be returned. No null exception will be thrown. 
    /// </para>
    /// <author>Contributed by Taylor Love (Pangamma)</author>
    /// </summary>
    /// <typeparam name="T"></typeparam>
    /// <param name="p_self"></param>
    /// <returns></returns>
    public static T? ToNullable<T>(this string p_self) where T : struct
    {
        if (!string.IsNullOrEmpty(p_self))
        {
            var converter = System.ComponentModel.TypeDescriptor.GetConverter(typeof(T));
            if (converter.IsValid(p_self)) return (T)converter.ConvertFromString(p_self);
            if (typeof(T).IsEnum) { T t; if (Enum.TryParse<T>(p_self, out t)) return t;}
        }

        return null;
    }

https://github.com/Pangamma/PangammaUtilities-CSharp/tree/master/src/StringExtensions

Mohammadreza Askari · Accepted Answer · 2021-11-28 10:05:32Z

0

this is what I using, maybe useful for someone!

public static class EnumExtension
{
    public static TEnum? ParseOrDefault<TEnum>(string value, bool ignoreCase = false, TEnum? @default = default)
        where TEnum : struct, Enum
    {
        TEnum? @enum;
        try { @enum = (TEnum)Enum.Parse(typeof(TEnum), value, ignoreCase); }
        catch { @enum = @default; }
        return @enum;
    }
}

answered Nov 28, 2021 at 10:05

Mohammadreza Askari

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