Calendaring Feats: Understanding Dates and Dayparts

Is it the weekend, yet? The answer isn’t quite as straightforward as it seems. In this talk, we'll discuss considerations for developing features displaying dates and times at an international scale. We'll walk through a few common pitfalls when working with Foundation's Calendar and DateInterval APIs and evaluate how dependency injection and test driven development can be used to prevent bugs around the world.

Presented at iOSoHo - November 2017

Transcript

1. iOSoHo - November 2017 Laura Ragone Calendaring Feats Understanding Dates and Dayparts
2. In the constellation of apps… iOSoHo - November 2017 Laura Ragone
3. …Meetup is a calendar iOSoHo - November 2017 Laura Ragone
4. “[…] I am unable to find meetups as easily as I did before.” “There is no apparent way to filter meetups” “[…] if I have to dig to find stuff that’s a dealbreaker.” iOSoHo - November 2017 Laura Ragone
5. - Video -
6. iOSoHo - November 2017 Laura Ragone • Date filtering Adapt ranges relative to the current day • Time filtering Adapt intervals to the user’s language and locale FIND EVENTS BY DATE AND TIME Filtered Meetups
7. Today, we’ll discuss… What makes working with dates and times so difficult 1 2 Common mistakes when working with datetime 3 How TDD and dependency injection can help iOSoHo - November 2017 Laura Ragone
8. What makes calendars difficult?
9. • The de facto calendar has not remained constant throughout history • Lunar → Solar • Roman calendar → Julian Calendar → Gregorian Calendar • Cultural variations A Brief History of Datetime iOSoHo - November 2017 Laura Ragone
10. Supported Calendars iOSoHo - November 2017 Laura Ragone
11. Is the first day of the week Sunday or Monday? …or Saturday? Additional Constraints iOSoHo - November 2017 Laura Ragone
12. Additional Constraints: When is the weekend? iOSoHo - November 2017 Laura Ragone Friday - Saturday Saturday - Sunday
13. Is it made up of multiple, contiguous days? Additional Constraints: When is the weekend? iOSoHo - November 2017 Laura Ragone
14. …Is it made up of multiple days? Additional Constraints: When is the weekend? iOSoHo - November 2017 Laura Ragone
15. Assume nothing
16. iOSoHo - November 2017 Laura Ragone • Date filters • Any day • Today • Tomorrow • This week • This weekend • Next week • Next weekend FIND EVENTS BY DATE AND TIME Filtered Meetups
17. Defining Date Filters iOSoHo - November 2017 Laura Ragone enum DateFilter { case any case today case tomorrow case thisWeek case thisWeekend case nextWeek case nextWeekend } • Date filters • Any day • Today • Tomorrow • This week • This weekend • Next week • Next weekend
18. Defining Date Intervals iOSoHo - November 2017 Laura Ragone
19. Defining Date Intervals iOSoHo - November 2017 Laura Ragone func dateInterval(from currentDate: Date = Date(), in calendar: Calendar = .current) -> DateInterval? { switch self { case .any: // ... case .today: // ... case .tomorrow: // ... case .thisWeek: // ... case .thisWeekend: // ... case .nextWeek: // ... case .nextWeekend: // ... } }
20. Defining Date Intervals: Any iOSoHo - November 2017 Laura Ragone switch self { case .any: return nil // ... }
21. Defining Date Intervals: Today iOSoHo - November 2017 Laura Ragone // ... case .today: return calendar.dateInterval(of: .day, for: currentDate) // ...
22. Defining Date Intervals: Tomorrow iOSoHo - November 2017 Laura Ragone // ... case .tomorrow: guard let todayInterval = DateFilter.today.dateInterval(from: currentDate, in: calendar) else { return nil } let startDate = todayInterval.end return calendar.dateInterval(of: .day, for: startDate) // ...
23. Defining Date Intervals: This week iOSoHo - November 2017 Laura Ragone // ... case .thisWeek: return calendar.dateInterval(of: .weekOfMonth, for: currentDate) // ... }
24. Defining Date Intervals: Next week iOSoHo - November 2017 Laura Ragone // ... case .nextWeek: guard let thisWeekInterval = DateFilter.thisWeek.dateInterval(from: currentDate, in: calendar) else { return nil } let startDate = thisWeekInterval.end return calendar.dateInterval(of: .weekOfMonth, for: startDate) // ...
25. A Look at Date Components iOSoHo - November 2017 Laura Ragone
26. A Look at Date Components iOSoHo - November 2017 Laura Ragone
27. A Look at Date Components: This week iOSoHo - November 2017 Laura Ragone // First, extract date components from the current date object. let currentDateComponents = calendar.dateComponents(in: calendar.timeZone, from: currentDate) // Next, use these current date's `DateComponents` to define the start date for "this week". let startDateComponents = DateComponents(calendar: calendar, timeZone: calendar.timeZone, month: currentDateComponents.month, weekOfYear: currentDateComponents.weekOfYear, yearForWeekOfYear: currentDateComponents.yearForWeekOfYear) // Then, create a start `Date` object from those date components. let startDate = calendar.date(from: startDateComponents)
28. A Look at Date Components: This week iOSoHo - November 2017 Laura Ragone // . . . // Create another `DateComponents` by incrementing the appropriate component. let endDateComponents = DateComponents(calendar: calendar, timeZone: calendar.timeZone, month: currentDateComponents.month, // Did I mention individual date components are optional? weekOfYear: currentDateComponents.weekOfYear! + 1, yearForWeekOfYear: currentDateComponents.yearForWeekOfYear) // Finally, create the end `Date` object. let endDate = calendar.date(from: endDateComponents)
29. Don’t fight the framework
30. Defining Date Intervals: This weekend iOSoHo - November 2017 Laura Ragone // ... case .thisWeekend: if calendar.isDateInWeekend(currentDate) { return calendar.dateIntervalOfWeekend(containing: currentDate) } else { return calendar.nextWeekend(startingAfter: currentDate) } // ...
31. …Does it work?
32. Test Driven Development (TDD) Tests are written in advance of the code 1 2 Code is revised until all tests pass iOSoHo - November 2017 Laura Ragone
33. Dependency Injection Decouples code from other dependencies, like instances controlled at the system level 1 2 Method Injection + default parameters = iOSoHo - November 2017 Laura Ragone
34. Dependency Injection iOSoHo - November 2017 Laura Ragone func dateInterval(from currentDate: Date = Date(), in calendar: Calendar = .current) -> DateInterval? { // ... } let _ = DateFilter.thisWeekend.dateInterval()
35. iOSoHo - November 2017 Laura Ragone DATE FORMATTERS Common Pitfalls Beware off-by-one errors when formatting dates for display Every nanosecond counts!
36. iOSoHo - November 2017 Laura Ragone • Time filters • Any time • Morning • Afternoon • Evening • Night FIND EVENTS BY DATE AND TIME Filtered Meetups
37. • Dayparts vary by language and locale • Time intervals associated with dayparts differ Time Filters iOSoHo - November 2017 Laura Ragone
38. Common Locale Data Repository (CLDR) iOSoHo - November 2017 Laura Ragone
39. <dayPeriodRules locales="en"> <dayPeriodRule type="midnight" at="00:00"/> <!-- midnight --> <dayPeriodRule type="noon" at="12:00"/> <!-- noon --> <dayPeriodRule type="morning1" from="06:00" before="12:00"/> <!-- morning --> <dayPeriodRule type="afternoon1" from="12:00" before="18:00"/> <!-- afternoon --> <dayPeriodRule type="evening1" from="18:00" before="21:00"/> <!-- evening --> <dayPeriodRule type="night1" from="21:00" before="06:00"/> <!-- night --> </dayPeriodRules> CLDR: TL;DR iOSoHo - November 2017 Laura Ragone
40. A Wrinkle in Time: Reverse Intervals iOSoHo - November 2017 Laura Ragone <dayPeriodRule type="night1" from="21:00" before="06:00"/> <!-- night -->
41. <dayPeriodRules locales="de"> <dayPeriodRule type="midnight" at="00:00"/> <!-- Mitternacht --> <dayPeriodRule type="morning1" from="05:00" before="10:00"/> <!-- Morgen —> <dayPeriodRule type="morning2" from=“10:00" before="12:00"/> <!-- Vormittag --> <dayPeriodRule type="afternoon1" from="12:00" before="13:00"/> <!-- Mittag —> <dayPeriodRule type="afternoon2" from="13:00" before="18:00"/> <!-- Nachmittag --> <dayPeriodRule type="evening1" from="18:00" before="24:00"/> <!-- Abend --> <dayPeriodRule type="night1" from="00:00" before="05:00"/> <!-- Nacht --> </dayPeriodRules> A Wrinkle in Time: 24:00 iOSoHo - November 2017 Laura Ragone
42. <dayPeriodRule type="evening1" from="18:00" before="24:00"/> <!-- Abend --> A Wrinkle in Time: 24:00 iOSoHo - November 2017 Laura Ragone
43. • Considerations when working with dates and times in an international app • Common pitfalls to avoid • TDD and Dependency Injection Today, we discussed… iOSoHo - November 2017 Laura Ragone
44. • Your Calendrical Fallacy is… - Knowledge paddles • http://yourcalendricalfallacyis.com • CLDR Day Periods - Unicode standardized time ranges • http://www.unicode.org/cldr/charts/32/supplemental/day_periods.html • Solutions to Common Date and Time Challenges - WWDC 2013: Session 227 • https://developer.apple.com/videos/play/wwdc2013/227/ Additional Resources iOSoHo - November 2017 Laura Ragone
45. Thanks!