Calculations on time

jhagerup

Member
Licensed User
Hi

Can anyone explain why this:

DateTime.TimeFormat="HH:mm:ss"
Log(DateTime.Time(DateTime.TimeParse("15:00:00")-DateTime.TimeParse("14:00:00")))

will give "02:00:00" and not "01:00:00" as expected ?

/jan
 

jhagerup

Member
Licensed User
Hi Erel

Thanks, it works, but I don't understand why.

Subtracting Two "datetime" values (in same Timezone) should give the correct difference.
My original problem is/was that I want to calculate the difference between a timestamp (DateTime.now) and some datetime in the past.
The DateTime.Now returns in my timezone - or at least shows the correct values with DateTime.Time(DateTime.Now).
But a DateTime.TimeParse("sometime") returns a different time than "sometime" and not in my timezone.

The solution (based on your suggestion) was to save the Timestamp in my timezone, SetTimeZone(0), do the TimeParse and then SetTimeZone(MyTimezone).

/jan
 

Erel

Administrator
Staff member
Licensed User
The problem is in the usage of DateTime.Time to convert ticks which do not represent an actual point of time to string.

You can use a custom method such as:
B4X:
Sub ConvertTicksToTimeString(t As Long) As String
    Dim days, hours, minutes, seconds As Int
    days = t / DateTime.TicksPerDay
    hours = (t Mod DateTime.TicksPerDay) / DateTime.TicksPerHour
    minutes = (t Mod DateTime.TicksPerHour) / DateTime.TicksPerMinute
    seconds = (t Mod DateTime.TicksPerMinute) / DateTime.TicksPerSecond
    Return days & " days, " & NumberFormat(hours, 2, 0) & " hours, " _
        & NumberFormat(minutes, 2, 0) & " minutes and " & NumberFormat(seconds, 2, 0) & " seconds"
End Sub
DateTime.Time(Ticks As Long) method, expects a value which represents the number of milliseconds passed since 1/1/1970, measured in UTC time zone (GMT).

If you pass 0 to this method you will get 1/1/1970 00:00 (GMT) converted to your time zone. It can even be more confusing if day light saving time is active or not.
 

jhagerup

Member
Licensed User
Thanks again.

The "little" hint that DateTime.Time expects UTC time was the clue.
Please update the wiki with very important information.

/jan
 

jeronimovilar2

Member
Licensed User
how to sum hours?

I need to sum the hours day by day:
10:00:00
08:00:00
08:00:00
----------
26:00:00

how can i do this?

sorry my english
 
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