How to serialize a TimeSpan to XML

Question

This is only a slight modification on the approach suggested in the question, but this Microsoft Connect issue recommends using a property for serialization like this:

[XmlIgnore]
public TimeSpan TimeSinceLastEvent
{
    get { return m_TimeSinceLastEvent; }
    set { m_TimeSinceLastEvent = value; }
}

// XmlSerializer does not support TimeSpan, so use this property for 
// serialization instead.
[Browsable(false)]
[XmlElement(DataType="duration", ElementName="TimeSinceLastEvent")]
public string TimeSinceLastEventString
{
    get 
    { 
        return XmlConvert.ToString(TimeSinceLastEvent); 
    }
    set 
    { 
        TimeSinceLastEvent = string.IsNullOrEmpty(value) ?
            TimeSpan.Zero : XmlConvert.ToTimeSpan(value); 
    }
}

This would serialize a TimeSpan of 0:02:45 as:

<TimeSinceLastEvent>PT2M45S</TimeSinceLastEvent>

Alternatively, the DataContractSerializer supports TimeSpan.

The way you've already posted is probably the cleanest. If you don't like the extra property, you could implement IXmlSerializable, but then you have to do everything, which largely defeats the point. I'd happily use the approach you've posted; it is (for example) efficient (no complex parsing etc), culture independent, unambiguous, and timestamp-type numbers are easily and commonly understood.

As an aside, I often add:

[Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]

This just hides it in the UI and in referencing dlls, to avoid confusion.

Something that can work in some cases is to give your public property a backing field, which is a TimeSpan, but the public property is exposed as a string.

eg:

protected TimeSpan myTimeout;
public string MyTimeout 
{ 
    get { return myTimeout.ToString(); } 
    set { myTimeout = TimeSpan.Parse(value); }
}

This is ok if the property value is used mostly w/in the containing class or inheriting classes and is loaded from xml configuration.

The other proposed solutions are better if you want the public property to be a usable TimeSpan value for other classes.

Combining an answer from Color serialization and this original solution (which is great by itself) I got this solution:

[XmlElement(Type = typeof(XmlTimeSpan))]
public TimeSpan TimeSinceLastEvent { get; set; }

where XmlTimeSpan class is like this:

public class XmlTimeSpan
{
    private const long TICKS_PER_MS = TimeSpan.TicksPerMillisecond;

    private TimeSpan m_value = TimeSpan.Zero;

    public XmlTimeSpan() { }
    public XmlTimeSpan(TimeSpan source) { m_value = source; }

    public static implicit operator TimeSpan?(XmlTimeSpan o)
    {
        return o == null ? default(TimeSpan?) : o.m_value;
    }

    public static implicit operator XmlTimeSpan(TimeSpan? o)
    {
        return o == null ? null : new XmlTimeSpan(o.Value);
    }

    public static implicit operator TimeSpan(XmlTimeSpan o)
    {
        return o == null ? default(TimeSpan) : o.m_value;
    }

    public static implicit operator XmlTimeSpan(TimeSpan o)
    {
        return o == default(TimeSpan) ? null : new XmlTimeSpan(o);
    }

    [XmlText]
    public long Default
    {
        get { return m_value.Ticks / TICKS_PER_MS; }
        set { m_value = new TimeSpan(value * TICKS_PER_MS); }
    }
}

You could create a light wrapper around the TimeSpan struct:

namespace My.XmlSerialization
{
    public struct TimeSpan : IXmlSerializable
    {
        private System.TimeSpan _value;

        public static implicit operator TimeSpan(System.TimeSpan value)
        {
            return new TimeSpan { _value = value };
        }

        public static implicit operator System.TimeSpan(TimeSpan value)
        {
            return value._value;
        }

        public XmlSchema GetSchema()
        {
            return null;
        }

        public void ReadXml(XmlReader reader)
        {
            _value = System.TimeSpan.Parse(reader.ReadContentAsString());
        }

        public void WriteXml(XmlWriter writer)
        {
            writer.WriteValue(_value.ToString());
        }
    }
}

Sample serialized result:

<Entry>
  <StartTime>2010-12-06T08:45:12.5</StartTime>
  <Duration>2.08:29:35.2500000</Duration>
</Entry>