Tatham Oddie

The documentation for System.TimeZoneInfo.GetSystemTimeZones() states:

Returns a sorted collection of all the time zones about which information is available on the local system.

Unfortunately, while the result is technically sorted, it’s a silly sort which shows GMT, then the eastern hemisphere, then the western hemisphere. It seems to be sorted by TimeZoneInfo.DisplayName instead of TimeZoneInfo.BaseUtcOffset.

Luckily this is easily fixed (and concise too thanks to anonymous methods!).

List<TimeZoneInfo> timeZones = new List<TimeZoneInfo>(TimeZoneInfo.GetSystemTimeZones());
timeZones.Sort(delegate(TimeZoneInfo left, TimeZoneInfo right) {
    int comparison = left.BaseUtcOffset.CompareTo(right.BaseUtcOffset);
    return comparison == 0 ? string.CompareOrdinal(left.DisplayName, right.DisplayName) : comparison;
});

In the devil’s language (VB.NET) you can achieve it using some slightly different code (no anonymous methods in VB.NET):

Dim timeZones As List(Of TimeZoneInfo) = New List(Of TimeZoneInfo)(TimeZoneInfo.GetSystemTimeZones())
timeZones.Sort(New Comparison(Of TimeZoneInfo)(AddressOf CompareTimeZones))

Private Function CompareTimeZones(ByVal left As TimeZoneInfo, ByVal right As TimeZoneInfo) As Integer
    Return IIf(comparison = 0, String.CompareOrdinal(left.DisplayName, right.DisplayName), comparison)
End Function

This will result in the list being sorted in the same order that you see under “Adjust Date/Time” in Windows.

Maybe they could fix this in the next release. To help make that happen, vote for the issue on Microsoft Connect.

Update – 5 Feb 08: Daniella asked for a VB.NET version, so I’ve updated the post with one. Because VB.NET doesn’t support anonymous methods, you need an extra function somewhere to do the comparison.

Update – 12 Feb 08: Whitney correctly pointed out that the order still wasn’t quite right for time zones that shared the same offset. We need to sort by name as well. I’ve updated the C# and VB.NET version accordingly. I changed Whitney’s version a bit to use the conditional operator so that I could avoid two return statements, as well as translating it to VB.NET. Thanks Whitney!

Update – 15 Feb 08: Added Microsoft Connect link.

Any ideas greatly appreciated!

I’ll update this post with a solution if / when I find one.