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TimeZoneInfo.GetSystemTimeZones Method

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

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
Public Shared Function GetSystemTimeZones As ReadOnlyCollection(Of TimeZoneInfo)

Return Value

Type: System.Collections.ObjectModel.ReadOnlyCollection(Of TimeZoneInfo)
A read-only collection of TimeZoneInfo objects.

ExceptionCondition
OutOfMemoryException

There is insufficient memory to store all time zone information.

SecurityException

The user does not have permission to read from the registry keys that contain time zone information.

The GetSystemTimeZones method retrieves all available time zone information from the subkeys of the registry's HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Time Zones key. If it is unable to successfully retrieve and parse values for particular string properties of individual TimeZoneInfo objects, this method sets their value to an empty string ("").

Important noteImportant

The GetSystemTimeZones method returns a collection of TimeZoneInfo objects only for time zones defined in the registry. It does not include time zones created using the overloads of the CreateCustomTimeZone method. These are accessible only through the object reference returned by the time zone creation method.

The collection returned by this method is sorted by display name using the current culture. For information about the display name, see DisplayName.

The ReadOnlyCollection(Of T) object returned by this method supports the IEnumerable(Of T) interface, which means that it can be iterated using the foreach (in C#) or For Each…Next (in Visual Basic) statements. Each iteration of the loop provides the next TimeZoneInfo object in the collection.

The collection of TimeZoneInfo objects represents time zones defined on the local computer; it does not necessarily provide complete information for all time zones during all time periods. If your application requires time zones not found on the local computer, you can create custom time zones using the overloads of the CreateCustomTimeZone method. For more information, see How to: Create Time Zones Without Adjustment Rules and How to: Create Time Zones with Adjustment Rules.

You can also determine whether an individual time zone is defined on the local computer by calling the FindSystemTimeZoneById method and providing the identifier of the time zone you want to retrieve as a parameter.

The following example retrieves a collection of time zone objects that represent the time zones defined on a computer and writes information about them to a text file.

Imports System.Collections.ObjectModel
Imports System.Globalization
Imports System.IO

Module Example
   Public Sub Main()
      Const OUTPUTFILENAME As String = "C:\Temp\TimeZoneInfo.txt" 

      Dim timeZones As ReadOnlyCollection(Of TimeZoneInfo) = TimeZoneInfo.GetSystemTimeZones() 
      Dim sw As StreamWriter = New StreamWriter(OUTPUTFILENAME, False)

      For Each timeZone As TimeZoneInfo in timeZones
         Dim hasDST As Boolean = timeZone.SupportsDaylightSavingTime
         Dim offsetFromUtc As TimeSpan = timeZone.BaseUtcOffset
         Dim adjustRules() As System.TimeZoneInfo.AdjustmentRule
         Dim offsetString As String

         sw.WriteLine("ID: {0}", timeZone.Id)
         sw.WriteLine("   Display Name: {0, 40}", timeZone.DisplayName)
         sw.WriteLine("   Standard Name: {0, 39}", timeZone.StandardName)
         sw.Write("   Daylight Name: {0, 39}", timeZone.DaylightName)
         sw.Write(iif(hasDST, "   ***Has ", "   ***Does Not Have "))
         sw.WriteLine("Daylight Saving Time***")
         offsetString = String.Format("{0} hours, {1} minutes", offsetFromUtc.Hours, offsetFromUtc.Minutes)
         sw.WriteLine("   Offset from UTC: {0, 40}", offsetString)
         adjustRules = timeZone.GetAdjustmentRules()
         sw.WriteLine("   Number of adjustment rules: {0, 26}", adjustRules.Length)  
         If adjustRules.Length > 0 Then
            sw.WriteLine("   Adjustment Rules:")
            For Each rule As TimeZoneInfo.AdjustmentRule In adjustRules
               Dim transTimeStart As TimeZoneInfo.TransitionTime = rule.DaylightTransitionStart
               Dim transTimeEnd As TimeZoneInfo.TransitionTime = rule.DaylightTransitionEnd 

               sw.WriteLine("      From {0} to {1}", rule.DateStart, rule.DateEnd)
               sw.WriteLine("      Delta: {0}", rule.DaylightDelta)
               If Not transTimeStart.IsFixedDateRule
                  sw.WriteLine("      Begins at {0:t} on {1} of week {2} of {3}", transTimeStart.TimeOfDay, _
                                                                                transTimeStart.DayOfWeek, _
                                                                                transTimeStart.Week, _
                                                                                MonthName(transTimeStart.Month))
                  sw.WriteLine("      Ends at {0:t} on {1} of week {2} of {3}", transTimeEnd.TimeOfDay, _
                                                                                transTimeEnd.DayOfWeek, _
                                                                                transTimeEnd.Week, _
                                                                                MonthName(transTimeEnd.Month))
               Else
                  sw.WriteLine("      Begins at {0:t} on {1} {2}", transTimeStart.TimeOfDay, _
                                                                 transTimeStart.Day, _
                                                                 MonthName(transTimeStart.Month))
                  sw.WriteLine("      Ends at {0:t} on {1} {2}", transTimeEnd.TimeOfDay, _
                                                               transTimeEnd.Day, _
                                                               MonthName(transTimeEnd.Month))
               End If 
            Next 
         End If             
      Next
      sw.Close()

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1
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