TimeZoneInfo.TransitionTime.IsFixedDateRule Property
Important
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Gets a value indicating whether the time change occurs at a fixed date and time (such as November 1) or a floating date and time (such as the last Sunday of October).
public:
property bool IsFixedDateRule { bool get(); };
public bool IsFixedDateRule { get; }
member this.IsFixedDateRule : bool
Public ReadOnly Property IsFixedDateRule As Boolean
true
if the time change rule is fixed-date; false
if the time change rule is floating-date.
The following example lists the transition times to and from daylight saving time for all time zones that are available on the local system. For time zones with fixed-date rules, it displays transition time information from the properties of the TimeZoneInfo.TransitionTime object. For time zones without fixed-date rules, it uses a Calendar object that represents the current system calendar to determine the actual start and end dates of the transition. The example displays the results to the console.
private void GetTransitionTimes(int year)
{
// Instantiate DateTimeFormatInfo object for month names
DateTimeFormatInfo dateFormat = CultureInfo.CurrentCulture.DateTimeFormat;
// Get and iterate time zones on local computer
ReadOnlyCollection<TimeZoneInfo> timeZones = TimeZoneInfo.GetSystemTimeZones();
foreach (TimeZoneInfo timeZone in timeZones)
{
Console.WriteLine("{0}:", timeZone.StandardName);
TimeZoneInfo.AdjustmentRule[] adjustments = timeZone.GetAdjustmentRules();
int startYear = year;
int endYear = startYear;
if (adjustments.Length == 0)
{
Console.WriteLine(" No adjustment rules.");
}
else
{
TimeZoneInfo.AdjustmentRule adjustment = GetAdjustment(adjustments, year);
if (adjustment == null)
{
Console.WriteLine(" No adjustment rules available for this year.");
continue;
}
TimeZoneInfo.TransitionTime startTransition, endTransition;
// Determine if starting transition is fixed
startTransition = adjustment.DaylightTransitionStart;
// Determine if starting transition is fixed and display transition info for year
if (startTransition.IsFixedDateRule)
Console.WriteLine(" Begins on {0} {1} at {2:t}",
dateFormat.GetMonthName(startTransition.Month),
startTransition.Day,
startTransition.TimeOfDay);
else
DisplayTransitionInfo(startTransition, startYear, "Begins on");
// Determine if ending transition is fixed and display transition info for year
endTransition = adjustment.DaylightTransitionEnd;
// Does the transition back occur in an earlier month (i.e.,
// the following year) than the transition to DST? If so, make
// sure we have the right adjustment rule.
if (endTransition.Month < startTransition.Month)
{
endTransition = GetAdjustment(adjustments, year + 1).DaylightTransitionEnd;
endYear++;
}
if (endTransition.IsFixedDateRule)
Console.WriteLine(" Ends on {0} {1} at {2:t}",
dateFormat.GetMonthName(endTransition.Month),
endTransition.Day,
endTransition.TimeOfDay);
else
DisplayTransitionInfo(endTransition, endYear, "Ends on");
}
}
}
private static TimeZoneInfo.AdjustmentRule GetAdjustment(TimeZoneInfo.AdjustmentRule[] adjustments,
int year)
{
// Iterate adjustment rules for time zone
foreach (TimeZoneInfo.AdjustmentRule adjustment in adjustments)
{
// Determine if this adjustment rule covers year desired
if (adjustment.DateStart.Year <= year && adjustment.DateEnd.Year >= year)
return adjustment;
}
return null;
}
private void DisplayTransitionInfo(TimeZoneInfo.TransitionTime transition, int year, string label)
{
// For non-fixed date rules, get local calendar
Calendar cal = CultureInfo.CurrentCulture.Calendar;
// Get first day of week for transition
// For example, the 3rd week starts no earlier than the 15th of the month
int startOfWeek = transition.Week * 7 - 6;
// What day of the week does the month start on?
int firstDayOfWeek = (int) cal.GetDayOfWeek(new DateTime(year, transition.Month, 1));
// Determine how much start date has to be adjusted
int transitionDay;
int changeDayOfWeek = (int) transition.DayOfWeek;
if (firstDayOfWeek <= changeDayOfWeek)
transitionDay = startOfWeek + (changeDayOfWeek - firstDayOfWeek);
else
transitionDay = startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek);
// Adjust for months with no fifth week
if (transitionDay > cal.GetDaysInMonth(year, transition.Month))
transitionDay -= 7;
Console.WriteLine(" {0} {1}, {2:d} at {3:t}",
label,
transition.DayOfWeek,
new DateTime(year, transition.Month, transitionDay),
transition.TimeOfDay);
}
open System
open System.Globalization
let displayTransitionInfo (transition: TimeZoneInfo.TransitionTime) year label =
// For non-fixed date rules, get local calendar
let cal = CultureInfo.CurrentCulture.Calendar
// Get first day of week for transition
// For example, the 3rd week starts no earlier than the 15th of the month
let startOfWeek = transition.Week * 7 - 6
// What day of the week does the month start on?
let firstDayOfWeek = cal.GetDayOfWeek(DateTime(year, transition.Month, 1)) |> int
// Determine how much start date has to be adjusted
let changeDayOfWeek = int transition.DayOfWeek
let transitionDay =
if firstDayOfWeek <= changeDayOfWeek then
startOfWeek + (changeDayOfWeek - firstDayOfWeek)
else
startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek)
// Adjust for months with no fifth week
let transitionDay =
if transitionDay > cal.GetDaysInMonth(year, transition.Month) then
transitionDay - 7
else
transitionDay
printfn $" {label} {transition.DayOfWeek}, {DateTime(year, transition.Month, transitionDay):d} at {transition.TimeOfDay:t}"
let getAdjustment (adjustments: TimeZoneInfo.AdjustmentRule seq) year =
adjustments
// Iterate adjustment rules for time zone
// Determine if this adjustment rule covers year desired
|> Seq.tryFind (fun adjustment -> adjustment.DateStart.Year <= year && adjustment.DateEnd >= DateTime year)
|> Option.defaultValue null
let getTransitionTimes year =
// Instantiate DateTimeFormatInfo object for month names
let dateFormat = CultureInfo.CurrentCulture.DateTimeFormat
// Get and iterate time zones on local computer
let timeZones = TimeZoneInfo.GetSystemTimeZones()
for timeZone in timeZones do
printfn $"{timeZone.StandardName}:"
let adjustments = timeZone.GetAdjustmentRules()
let startYear = year
let mutable endYear = startYear
if adjustments.Length = 0 then
printfn " No adjustment rules."
else
let adjustment = getAdjustment adjustments year
if adjustment = null then
Console.WriteLine(" No adjustment rules available for this year.")
else
// Determine if starting transition is fixed
let startTransition = adjustment.DaylightTransitionStart
// Determine if starting transition is fixed and display transition info for year
if startTransition.IsFixedDateRule then
printfn $" Begins on {dateFormat.GetMonthName startTransition.Month} {startTransition.Day} at {startTransition.TimeOfDay:t}"
else
displayTransitionInfo startTransition startYear "Begins on"
// Determine if ending transition is fixed and display transition info for year
let mutable endTransition = adjustment.DaylightTransitionEnd
// Does the transition back occur in an earlier month (i.e.,
// the following year) than the transition to DST? If so, make
// sure we have the right adjustment rule.
if endTransition.Month < startTransition.Month then
endTransition <- (getAdjustment adjustments (year + 1)).DaylightTransitionEnd
endYear <- endYear + 1
if endTransition.IsFixedDateRule then
printfn $" Ends on {dateFormat.GetMonthName endTransition.Month} {endTransition.Day} at {endTransition.TimeOfDay:t}"
else
displayTransitionInfo endTransition endYear "Ends on"
Private Sub GetTransitionTimes(year As Integer)
' Get and iterate time zones on local computer
Dim timeZones As ReadOnlyCollection(Of TimeZoneInfo) = TimeZoneInfo.GetSystemTimeZones()
For Each timeZone As TimeZoneInfo In timeZones
Console.WriteLine("{0}:", timeZone.StandardName)
Dim adjustments() As TimeZoneInfo.AdjustmentRule = timeZone.GetAdjustmentRules()
Dim startYear As Integer = year
Dim endYear As Integer = startYear
If adjustments.Length = 0 Then
Console.WriteLine(" No adjustment rules.")
Else
Dim adjustment As TimeZoneInfo.AdjustmentRule = GetAdjustment(adjustments, year)
If adjustment Is Nothing Then
Console.WriteLine(" No adjustment rules available for this year.")
Continue For
End If
Dim startTransition, endTransition As TimeZoneInfo.TransitionTime
' Determine if starting transition is fixed
startTransition = adjustment.DaylightTransitionStart
' Determine if starting transition is fixed and display transition info for year
If startTransition.IsFixedDateRule Then
Console.WriteLine(" Begins on {0} {1} at {2:t}", _
MonthName(startTransition.Month), _
startTransition.Day, _
startTransition.TimeOfDay)
Else
DisplayTransitionInfo(startTransition, startYear, "Begins on")
End If
' Determine if ending transition is fixed and display transition info for year
endTransition = adjustment.DaylightTransitionEnd
' Does the transition back occur in an earlier month (i.e.,
' the following year) than the transition to DST? If so, make
' sure we have the right adjustment rule.
If endTransition.Month < startTransition.Month Then
endTransition = GetAdjustment(adjustments, year + 1).DaylightTransitionEnd
endYear += 1
End If
If endTransition.IsFixedDateRule Then
Console.WriteLine(" Ends on {0} {1} at {2:t}", _
MonthName(endTransition.Month), _
endTransition.Day, _
endTransition.TimeOfDay)
Else
DisplayTransitionInfo(endTransition, endYear, "Ends on")
End If
End If
Next
End Sub
Private Function GetAdjustment(adjustments As TimeZoneInfo.AdjustmentRule(), _
year As Integer) As TimeZoneInfo.AdjustmentRule
' Iterate adjustment rules for time zone
For Each adjustment As TimeZoneInfo.AdjustmentRule In adjustments
' Determine if this adjustment rule covers year desired
If adjustment.DateStart.Year <= year And adjustment.DateEnd.Year >= year Then
Return adjustment
End If
Next
Return Nothing
End Function
Private Sub DisplayTransitionInfo(transition As TimeZoneInfo.TransitionTime, year As Integer, label As String)
' For non-fixed date rules, get local calendar
Static cal As Calendar = CultureInfo.CurrentCulture.Calendar
' Get first day of week for transition
' For example, the 3rd week starts no earlier than the 15th of the month
Dim startOfWeek As Integer = transition.Week * 7 - 6
' What day of the week does the month start on?
Dim firstDayOfWeek As Integer = cal.GetDayOfWeek(New Date(year, transition.Month, 1))
' Determine how much start date has to be adjusted
Dim transitionDay As Integer
Dim changeDayOfWeek As Integer = transition.DayOfWeek
If firstDayOfWeek <= changeDayOfWeek Then
transitionDay = startOfWeek + (changeDayOfWeek - firstDayOfWeek)
Else
transitionDay = startOfWeek + (7 - firstDayOfWeek + changeDayOfWeek)
End If
' Adjust for months with no fifth week
If transitionDay > cal.GetDaysInMonth(year, transition.Month) Then
transitionDay -= 7
End If
Console.WriteLine(" {0} {1}, {2:d} at {3:t}", _
label, _
transition.DayOfWeek, _
New DateTime(year, transition.Month, transitionDay), _
transition.TimeOfDay)
End Sub
A fixed-date rule indicates that the transition occurs on the same date and time of each year to which the adjustment rule applies. For example, a time change that occurs every November 3 follows a fixed-date rule. A floating-date rule indicates that the transition occurs on a specific day of a specific week of a specific month for each year to which the adjustment rule applies. For example, a time change that occurs on the first Sunday of November follows a floating-date rule.
The value of the IsFixedDateRule property determines which properties of a TimeZoneInfo.TransitionTime object have valid values. The following table indicates which properties are affected by the value of the IsFixedDateRule property.
TransitionTime property | IsFixedDateRule = true | IsFixedDateRule = false |
---|---|---|
Day |
Valid | Unused |
DayOfWeek |
Unused | Valid |
Week |
Unused | Valid |
Month |
Valid | Valid |
TimeOfDay |
Valid | Valid |
Product | Versions |
---|---|
.NET | Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 2.0, 2.1 |
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