How to Convert ISO 8601 Duration to TimeSpan in VB.Net?

Question

Is there a standard library method that converts a string that has duration in the standard ISO 8601 Duration (also used in XSD for its duration type) format into the .NET TimeSpan object?

For example, P0DT1H0M0S which represents a duration of one hour, is converted into New TimeSpan(0,1,0,0,0).

A Reverse converter does exist which works as follows: Xml.XmlConvert.ToString(New TimeSpan(0,1,0,0,0)) The above expression will return P0DT1H0M0S.

Answer 1

This will convert from xs:duration to TimeSpan:

System.Xml.XmlConvert.ToTimeSpan("P0DT1H0M0S")

See http://msdn.microsoft.com/en-us/library/system.xml.xmlconvert.totimespan.aspx

Answer 2

One minor word of caution - XmlConvert.ToTimeSpan() is a little funny when working with months and years. The TimeSpan class does not have month or year members, probably because their length varies. However, ToTimeSpan() will happily accept a duration string with month or year values in it and guess at a duration, instead of throwing an exception. Observe:

PS C:\Users\troll> [Reflection.Assembly]::LoadWithPartialName("System.Xml")

GAC    Version        Location
---    -------        --------
True   v2.0.50727     C:\Windows\assembly\GAC_MSIL\System.Xml\2.0.0.0__b77a5c561934e089\System.Xml.dll


PS C:\Users\troll> [System.Xml.XmlConvert]::ToTimeSpan("P1M")


Days              : 30
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 0
Ticks             : 25920000000000
TotalDays         : 30
TotalHours        : 720
TotalMinutes      : 43200
TotalSeconds      : 2592000
TotalMilliseconds : 2592000000



PS C:\Users\troll> [System.Xml.XmlConvert]::ToTimeSpan("P1Y")


Days              : 365
Hours             : 0
Minutes           : 0
Seconds           : 0
Milliseconds      : 0
Ticks             : 315360000000000
TotalDays         : 365
TotalHours        : 8760
TotalMinutes      : 525600
TotalSeconds      : 31536000
TotalMilliseconds : 31536000000



PS C:\Users\troll>

Answer 3

As @ima dirty troll said TimeSpan translates always years as 365 days and months as 30 days.

TimeSpan ts = System.Xml.XmlConvert.ToTimeSpan("P5Y");
DateTime now = new DateTime(2008,2,29);
Console.WriteLine(now + ts); // 27/02/2013 0:00:00

To address it you should add each field individually rather than using TimeSpan.

DateTime now = new DateTime (2008, 2, 29);
string duration = "P1Y";
Regex expr = 
    new Regex (@"(-?)P((\d{1,4})Y)?((\d{1,4})M)?((\d{1,4})D)?(T((\d{1,4})H)?((\d{1,4})M)?((\d{1,4}(\.\d{1,3})?)S)?)?", RegexOptions.Compiled | RegexOptions.CultureInvariant);
bool positiveDuration = false == (input [0] == '-');

MatchCollection matches = expr.Matches (duration);
var g = matches [0];
Func<int,int> getNumber = x => {
    if (g.Groups.Count < x || string.IsNullOrEmpty (g.Groups [x].ToString ())) {
        return 0;
    }

    int a = int.Parse (g.Groups [x].ToString ());

    return PositiveDuration ? a : a * -1;

};
now.AddYears (getNumber (3));
now.AddMonths (getNumber (5));
now.AddDays (getNumber (7));
now.AddHours (getNumber (10));
now.AddMinutes (getNumber (12));
now.AddSeconds (getNumber (14));
Console.WriteLine (now); // 28/02/2012 0:00:00