SetTimeZone(0) before every DateTime methode?

[Pantelis]

SetTimeZone(0) before every DateTime method?

Hi all
I am trying this code and the result of c is not 01:00:00 if the timezone of my device is not 0.

Dim a As Long
   Dim b As Long
   Dim c As Long
   a = DateTime.Now
   b = a - DateTime.TicksPerHour

   Log (DateTime.Time(a))
   
   Log (DateTime.Time(b))
   
   c = a - b
   
   Log (DateTime.Time(c))

I order to have correct result i change the code like this:

Dim a As Long
   Dim b As Long
   Dim c As Long
   Dim Timezone As Double
   Timezone = DateTime.GetTimeZoneOffsetAt(DateTime.Now)
   
   a = DateTime.Now
   b = a - DateTime.TicksPerHour
   
   DateTime.SetTimeZone(0)
   
   Log (DateTime.Time(a))
   
   Log (DateTime.Time(b))
   
   c = a - b
   
   Log (DateTime.Time(c))
   
   DateTime.SetTimeZone(Timezone)

Is this correct way?

In what methods of the DateTime And the DateUtils this trick must be done in order to have correct results from them? What methods are affected by the timezone?

 

[Erel]

There is no need to set the time zone. What you are doing is incorrect.

There isn't any meaning to DateTime.Time(a - b). (a - b) doesn't represent the time instance that you are thinking of.

You should instead use DateUtils.PeriodBetween.

 

[Pantelis]

Thanks Erel. It was a bad example.

I read on forum that in order to have corrrect result with date and time calculations we must set timezone to 0. I try to see if this happens in any of datetime method and as i see i have wrong results from alot of them if timezone in not 0. So i set always the timezone to 0. The problem is that if i do that the DateTime.Now gives me UTC values.

How to use the DateTime.Now to get the real date-time value depending on device's settings TimeZone and DST?

 

[Erel]

You should not set the time zone to 0. Use DateUtils and everything will be fine.

 

[Pantelis]

I want to strip time off a date. I found this http://www.b4x.com/android/forum/threads/strip-time-off-a-date.15847/#post-90084
but it requires the TimeZone to be set to 0, otherwise it gives wrong results. Hot to do it with DateUtils?

 

[Erel]

This thread was created before DateUtils was available.

The correct code is:

Sub StripTime(Ticks As Long) As Long
   Return DateUtils.SetDateAndTime(DateTime.GetYear(Ticks), DateTime.GetMonth(Ticks), DateTime.GetDayOfMonth(Ticks), 0, 0, 0)
End Sub

 

[Pantelis]

Great. Thank you very much Erel.

 

[Pantelis]

Erel i try To understand why the old method while looks ok gives wrong result and found this.

I set the device with this settings:
Device settings:
date: 01/Jan/2013 (No DST on this time)
TimeZone: +3
Time: 10:00:00 AM
(Offset from UTC: +3)

    Dim InputDate, OnlyTime As Long
    InputDate = DateTime.Now

 
    OnlyTime = InputDate Mod DateTime.TicksPerDay
 
    Log(DateTime.time(OnlyTime))                'Original time 10:00:00 AM and Returns 10:00:00 AM. OK.
    Log(DateTime.GetHour(OnlyTime))                '10

Then i change the settings of device with:
Device settings:
date: 01/Jul/2013 (We have DST on this time)
TimeZone: +4
Time: 10:00:00 AM
(Offset from UTC: +4, (timezone +3 and DST +1))
and try the same code

Dim InputDate, OnlyTime As Long
    InputDate = DateTime.Now

 
    OnlyTime = InputDate Mod DateTime.TicksPerDay
 
    Log(DateTime.time(OnlyTime))                'Original time 10:00:00 AM and Returns 09:00:00 AM.
    Log(DateTime.GetHour(OnlyTime))                '9

DateTime.Time ignores the DST? The same happend with DateTime.Hour

 

[Erel]

Check DateTime.Date(OnlyTime). You will see why the DST is "ignored".

 

[Pantelis]

Of course. There is no DST in 1/1/1970. Thank you very much Erel.

 

[LucaMs]

I have the same problem (#1).

I can not use DateUtils because I need milliseconds.

(Why if I use:

DateTime.TimeFormat = "HH:mm:ss:SSS"
Dim NowStart as long
NowStart = DateTime.Now
' ...
Label1.Text = DateTime.Time(DateTime.Now - NowStart)
'It returns +1 hour

it does not work?)

The problem can not be related to "time zone" or other settings,
since both the initial and final time are used with the same settings.

If DateTime.Now is a Long value in milliseconds, the difference should be ... the difference in milliseconds!

 

[Erel]

There are several problems in your code. As a general rule date and time arithmetics are much more complicated than it may seem and should be avoided. Please start a new thread and explain the problem you are trying to solve.