How to TryParse for Enum value?

Question

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.

The function may not internally use try/catch, which excludes using Enum.Parse, which throws an exception when given an invalid argument.

I'd like to use something along the lines of a TryParse function to implement this:

public static TEnum ToEnum<TEnum>(this string strEnumValue, TEnum defaultValue) {    object enumValue;    if (!TryParse (typeof (TEnum), strEnumValue, out enumValue))    {        return defaultValue;    }    return (TEnum) enumValue; } 

Answer 1

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.

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 TryParse method was added in .NET 4.0.

Answer 2

As others have said, you have to implement your own TryParse. Simon Mourier is providing a full implementation which takes care of everything.

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.IsDefined with this string, it will return false, even though Enum.Parse handles it correctly.

Update

As mentioned by Lisa and Christian in the comments, Enum.TryParse is now available for C# in .NET4 and up.

MSDN Docs