Android Question DateTime.Now problem with time zones

[Arf]

Does DateTime.Now return the ticks since 1/1/1970 to GMT time or UTC, or to the time on the device in question?

I send the current time to my external device for storage, like this:

'now convert the time into it's parts
Dim timenow As Long = DateTime.Now
Dim calTime As spiroTime
calTime = Types.getDateFromTicks(timenow)
buf = Array As Byte(calTime.s,calTime.m,calTime.h,calTime.d,calTime.mo,calTime.y)
out.WriteBytes(buf,0,6)

The function called looks like this:

Sub getDateFromTicks(intime As Long) As spiroTime
    Dim outtime As spiroTime
    outtime.y = DateTime.GetYear(intime)-2000     'DateTime works from 1970, my device dates work from 2000
    outtime.mo = DateTime.GetMonth(intime)
    outtime.d = DateTime.GetDayOfMonth(intime)
    outtime.h = DateTime.GetHour(intime)
    outtime.m = DateTime.GetMinute(intime)
    outtime.s = DateTime.GetSecond(intime)
    Return outtime
End Sub

Then at some stage I read the stored date back from the device:

UnitInfo.Calibdate = Types.getDateInTicks(pk.pData(52),pk.pData(53),pk.pData(54),pk.pData(55),pk.pData(56),pk.pData(57))

The function looks like this:

Sub getDateInTicks(s As Int, m As Int, h As Int, d As Int, mo As Int, y As Int) As Long
    Dim result As Long
    result = s * DateTime.TicksPerSecond
    result = result + ( m * DateTime.TicksPerMinute)
    result = result + (h-1) * DateTime.TicksPerHour
    result = result + (d-1) * DateTime.TicksPerDay
    Dim mn, yr As Int
    mn = mo-1
    yr = y+30        'DateTime works from 1970, my device dates work from 2000
    result = DateTime.Add(result,yr,mn,0)
    Return result
End Sub

It all works fine for me in the UK, but someone is testing my app in the USA. Their tablet's time is set 12PM, EST in settings.
They store the time at 12:02, and it reads back as 06:02.

I'm having a bit of a struggle wrapping my head around it.

 

[Arf]

Ok so now I understand DateTime.Now is always UTC time.
So, I would like to keep storing the date in UTC, and convert the ticks that I read back, to local time.
I changed my function but it doesn't work:

Sub getDateInTicks(s As Int, m As Int, h As Int, d As Int, mo As Int, y As Int) As Long
    Dim result As Long
    result = s * DateTime.TicksPerSecond
    result = result + ( m * DateTime.TicksPerMinute)
    result = result + (h-1) * DateTime.TicksPerHour
    result = result + (d-1) * DateTime.TicksPerDay
    Dim mn, yr As Int
    mn = mo-1
    yr = y+30        'DateTime works from 1970, SpiroConnect works from 2000
    result = DateTime.Add(result,yr,mn,0)
    
    'now we need to adjust between UTC and local time
    Dim diff As Long
    
    'this should convert UTC time to a string rep of local time and then back into ticks, right?
    
    diff = DateTime.Now - DateTime.DateParse(DateTime.Date(DateTime.Now))
    result = result + diff
    'done
    
    Return result
End Sub

So the question is, how can I get the tick value for local time?

 

[Andrew (Digitwell)]

This forum thread will help

problem with TimeZone/Daylight

I have a date as string coming from a GPS system that need to be represented with the timezone and daylight saving settings. This is the code that works fine Dim dt As Long=DateTime.Dateparse("2018-03-25 02:01:22") dt=dt+(DateTime.GetTimeZoneOffsetAt(dt)*3600000)...

www.b4x.com

Also try using the timezoneoffset method

 

[Arf]

OK so I changed that function to this:

Sub getDateInTicks(s As Int, m As Int, h As Int, d As Int, mo As Int, y As Int) As Long
    Dim result As Long
    result = s * DateTime.TicksPerSecond
    result = result + ( m * DateTime.TicksPerMinute)
    result = result + (h-1) * DateTime.TicksPerHour
    result = result + (d-1) * DateTime.TicksPerDay
    Dim mn, yr As Int
    mn = mo-1
    yr = y+30        'DateTime works from 1970, SpiroConnect works from 2000
    result = DateTime.Add(result,yr,mn,0)
    
    'now we need to adjust between UTC and local time
    Dim diff As Long
    diff = DateTime.TimeZoneOffset * DateTime.TicksPerHour
    result = result - diff
    'done
    
    Return result
End Sub

Now I am much closer - one hour out! Which must be something to do with daylight savings then. I can't see any settings for daylight savings on my tablet though.

 

[Erel]

This code is (completely) wrong.

So the question is, how can I get the tick value for local time?

There is no such thing.
Ticks = number of milliseconds since 1/1/1970 00:00 UTC.

I recommend watching the date and time video tutorial: https://www.b4x.com/etp.html?vimeography_gallery=1&vimeography_video=256970493

DateTime.Date / Time will return a string that represents the local date / time.

 

[Arf]

Thanks Erel.
This is working now...

Sub getDateInTicks(s As Int, m As Int, h As Int, d As Int, mo As Int, y As Int) As Long
    Dim result As Long
    
    'convert the time to a string
    Dim timeString As StringBuilder
    timeString.Initialize
    timeString.Append(NumberFormat(d,2,0)).Append(":").Append(NumberFormat(mo,2,0)).Append(":").Append(NumberFormat2(y+2000,4,0,0,False)).Append(" ")
    timeString.Append(NumberFormat(h,2,0)).Append(":").Append(NumberFormat(m,2,0)).Append(":").Append(NumberFormat(s,2,0))

    Dim store As String = DateTime.DateFormat
    DateTime.DateFormat = "dd:MM:yyyy HH:mm:ss"
    result = DateTime.DateParse(timeString.ToString)
    DateTime.DateFormat = store
        
    Return result
End Sub

 

[Erel]

Why aren't you using DateUtils.SetDateAndTime???

 

[Arf]

I somehow missed seeing that function
I know for next time now! Thanks.