NumericUpDown Parses Decimal Value Incorrectly

[dkhughes]

The NumericUpDown control is improperly parsing a decimal value that is entered with no leading zero in the en-US culture. For example, .1 becomes 1.0, 0.105 becomes 105, etc.

What steps will reproduce this issue?

This is a really easy issue to reproduce. An entire working example showing the failure is:

    class Program
    {
        // The regex copy pasted out of numericupdown control file...
        private static readonly Regex RegexStringFormatNumber = new Regex(@"[-+]?(?<![0-9][.,])\b[0-9]+(?:[.,\s][0-9]+)*[.,]?[0-9]?(?:[eE][-+]?[0-9]+)?\b(?!\.[0-9])", RegexOptions.Compiled);

        static void Main(string[] args)
        {
            // returns 1
            string leadingdec = GetAnyNumberFromText(".1");
            
            // returns 0.1
            string leadingZero = GetAnyNumberFromText("0.1");

            // returns 0.1 in double
            double.TryParse(".1", out double leadingDecDouble);

            // also returns 0.1 in double
            double.TryParse("0.1", out double leadingZeroDouble);
        }

        // The GetAnyNumberFromText function copy pasted out of numericupdown control file...
        private static string GetAnyNumberFromText(string text)
        {
            var matches = RegexStringFormatNumber.Matches(text);
            if (matches.Count > 0)
            {
                return matches[0].Value;
            }
            return text;
        }
    }

Expected outcome

We expect the parsed value to match the value that double.Parse would return on the raw string. For this example, ".1" should parse to 0.1 not 1.0 which it does currently.

Environment

• MahApps.Metro: Latest master has issue
• Windows OS 10
• Visual Studio 2017
• .NET Framework 4.5

[dkhughes]

Altering the regexp to the following allows a leading decimal, but it may be too lenient for you:

@"[-+]?[0-9]?[.,]?\b[0-9]+(?:[.,\s][0-9]+)*[.,]?[0-9]?(?:[eE][-+]?[0-9]+)?\b(?!\.[0-9])"