Where’s February 29th? or Does Xojo.Core.Date have problems with leap years?

General
1

I have to design a calendar window that displays dates for each days of a month much like iCal.
So I built a canvas subclass that takes a xojo.core.date as parameter and then calculates a few things to determine the sizes:

[code] dim startdate as new xojo.core.date(CurrentDate.Year, CurrentDate.Month, 1, xojo.core.timezone.Current) // 1st of the month
dim d1 as integer = startdate.germandayofmonth // day of month rotated one left – we start the weeks here with Monday. Need this later.
dim enddate as xojo.core.date = startdate + new xojo.Core.DateInterval(0, 1) // First of the next month
enddate = enddate - new xojo.Core.DateInterval(0, 0, 1) // and one day back to get the last day of the current month.
dim d2 as integer = enddate.germandayofmonth

dim dif as xojo.Core.DateInterval = enddate - startdate
dim weeks as integer = dif.Days/7 // how many weeks did we have in the month?
dim rest as integer = dif.days mod 7 // and is there a rest?
if rest > 0 then weeks = weeks + 1 // if so, we need to draw one more week line.[/code]

This all works nicely, except for this month. We have a leap year, so I expected enddate would be 2-29-2016. It’s not. Xojo tells me we have no leap year and jumps to the 28th.
Is there any way I can fix this? Thanks a lot!

2

Have you tried subtracting 86400 seconds instead, or even 24 hrs?

3

Can you show us what the GermanDayOfMonth function looks like?

4

For what it’s worth, when I take out your GermanDayOfMonth method, EndDate ends up being Feb 29th. I’m guessing that it’s screwing with the actual day.

5

That’s weird! But thanks, Greg! I’ll figure out something else then.
The method, anyway, does not change the date. It’s a very clumsy “calculation”:

Function GermanDayOfMonth(extends d as xojo.core.date) As Integer dim result as integer = d.DayOfWeek - 1 if result = 0 then result = 7 return result End Function

6

[quote=245698:@Ulrich Bogun]That’s weird! But thanks, Greg! I’ll figure out something else then.
The method, anyway, does not change the date. It’s a very clumsy “calculation”:

Function GermanDayOfMonth(extends d as xojo.core.date) As Integer dim result as integer = d.DayOfWeek - 1 if result = 0 then result = 7 return result End Function[/quote]

It seems like you should keep your actual data in the proper Xojo.Core.Date and leave adjusting by the day of the week to your app’s user interface layer?

7

Well it turned out Dateinterval wasn’t such a good idea. It is too smart - when I want to add another day to get the number of days in that month it tells me the interval is 0 days and 1 month :wink:
Instead, I just calculate enddate.day - startdate.day + 1 now. Still don’t know why the extension method messed up the calculation, but I see a February with 29 days now. Thanks a lot, both of you!

9

Hehe, had myself confused in the numberofDays. Seems to run fine now, but I found a discrepancy between OS X and Linux framework (64 bit, the latter one). See the screenshot of the same project on both platforms, with a draw event

[code]Sub Paint(g As Graphics, areas() As REALbasic.Rect)
dim daywidth as double = me.Width / 7
g.ClearRect 0,0,me.Width, me.Height
g.ForeColor = color.lightgray
g.DrawLine 0,me.headsection,me.Width, me.headsection
system.debuglog HeadSection.ToText
g.TextSize = 28
g.DrawString MonthName+" "+YearText, 10, 32
for q as integer = 1 to 6
g.DrawLine qdaywidth, HeadSection, qdaywidth, me.Height
next
dim startdate as new xojo.core.date(CurrentDate.Year, CurrentDate.Month, 1, xojo.core.timezone.Current)

dim days as integer =CurrentDate.daysinMonth
dim weeks as integer = Days/7
dim rest as integer = days mod 7
dim startday as integer = startdate.germandayofweek
if rest > 0 then weeks = weeks + 1
if startday - 1 + rest > 7 then weeks = weeks + 1
dim dayheigth as double = (me.Height - HeadSection)/weeks
for q as integer = 1 to weeks -1
g.DrawLine 0, HeadSection+qdayheigth, me.Width, HeadSection+qdayheigth
next
for q as integer = 1 to weeks
for p as integer = 1 to 7
dim curday as new xojo.core.date (currentdate.year, CurrentDate.month, (q-1) * 7 + (p-startdate.germandayofweek+1), xojo.core.timezone.current)
ShowDay (g, curday, (p-1) * daywidth, HeadSection+ ((q-1)dayheigth), daywidth, dayheigth, currentdate)
next
next
for q as integer = 1 to 6
g.ForeColor = color.lightgray
g.DrawLine qdaywidth, HeadSection, qdaywidth, me.Height
g.ForeColor = color.white
g.DrawLine qdaywidth-1, HeadSection, q*daywidth-1, me.Height
next
End Sub[/code]

where DaysInMonth is this unelegant, but working method:

[code]Function DaysInMonth(extends d as xojo.Core.Date) As Integer
// Trouble with Xojo.core.dateinterval not replying correctly when GermanDayOfWeek is used, therefore:

dim firstday as new xojo.core.date(d.Year, d.Month, 1, 0,0,0, xojo.core.TimeZone.Current)
for q as integer = 31 downto 28
dim lastday as new xojo.core.date (firstday.year, firstday.Month, q, 0,0,0, xojo.core.timezone.current)
if lastday.Month = firstday.month then return q
next
End Function[/code]

(I can of course compare to d.month only, firstday isn’t necessary).

This results in negative Days on Linux:

I am sure I can work around that, but I suspect the framework should give the same results on all platforms, or can’t it?

10

It should.

11

Thanks, Joe. <https://xojo.com/issue/42457>

12

Also wrong on Windows. :frowning: