cocoa date time class chart

Click the chart to see it at full size.

swift kickIn the previous installment in this series that looks at working with dates and times in Cocoa, we looked at:

  • The NSDate class, which is the heart of date and time in Cocoa, and represents a single point in time relative to the start of the third millennium (midnight, January 1, 2001)
  • the NSCalendar class, which provides a context for dates and the ability to do date arithmetic,
  • the NSDateComponents class, which represents the parts that make up either a date or a span of time, and
  • the NSDateFormatter class, which turns dates into string representations and vice versa.

We also covered creating dates, converting components into dates and vice versa, and converting dates into strings and vice versa. With this knowledge under our belts, let’s get to this article’s topic: doing date calculations.

Creating a couple of dates to work with

valentines st patricks

Start with a fresh playground, and enter or paste the following code so it looks like this:

In the code above, we’re creating two dates in two different ways (which we covered in the previous article):

  • We’re creating Valentine’s Day (February 14 for those of you in places where it’s not celebrated) by setting up date components and then using the user’s calendar to convert the components into a date.
  • We’re creating St. Patrick’s Day (March 17 for those of you in places where it’s not celebrated) by converting a string representing that date into a date by means of a date formatter. You may find that if you need to instantiate a large number of dates in code, you may want to do so this way, as you can do it in far fewer lines than by using date components.

Now that we have a couple of date objects, let’s do some date arithmetic!

Which came first?

which came first

NSDate has two methods, earlierDate and laterDate, which compare one date to another and return the appropriate date. Add the highlighted code below so that your playground looks like this:

This is pretty straightforward: valentinesDay.earlierDate(stPatricksDay) returns the valentinesDay instance, while valentinesDay.laterDate(stPatricksDay) returns stPatricksDay.

NSDate has a compare method that works in a way similar to a lot of other “compare” methods (such as C’s strcmp) that compare a value a and b, where:

  • If a < b, it returns a negative number
  • if a == b, it returns 0
  • if a > b, it returns a positive number

Cocoa comparison methods return values of type NSComparisonResult, so that when you’re comparing two values a and b:

  • If a < b, it returns NSOrderedAscending
  • if a == b, it returns NSOrderedSame
  • if a > b, it returns NSOrderedDescending

Let’s take it out for a spin. Add the highlighted code below so that your playground looks like this:

Valentine’s Day comes before St. Patrick’s Day, so the result you see the in sidebar should be Valentine’s Day comes before St. Patrick’s Day.

Date arithmetic: How far apart are two dates and times?

countdown clock

NSDate has the timeIntervalSinceDate method, which gives you the difference between 2 dates…in seconds.

Since Valentine’s Day comes before St. Patrick’s Day, the first value is negative, while the second value is positive. Most users won’t find knowing that there are nearly 2.7 million seconds between the two days. How can we find out the number of days between Valentine’s and St. Patrick’s?

That’s where date components come in. I mentioned last time that date components can represent either:

  • A specific point in time, or
  • a duration of time.

We’re going to use date components for the second purpose in this example. We need to do the following:

  • Specify the units of time that we want from the calculation, which in this case is days, and
  • Provide those units of time and the two dates to NSCalendar‘s components method:

This version of NSCalendar‘s components method takes the following arguments:

  • unitFlags: a bitwise OR of NSCalendarUnit constants, which specify the units of the result. Since we want to know the number of days between Valentine’s and St. Patrick’s, we set this to the value NSCalendarUnit.DayCalendarUnit.
  • fromDate: The start date in the calculation.
  • toDate: The end date in the calculation.
  • options: In most cases, you’ll want this set to nil, which causes overflows in a unit to carry to the next higher unit. For example, if you specify in unitFlags that you want your result expressed in minutes and seconds, and the calculation’s result is 61 seconds, the result will be changed to 1 minute, 1 second.

Let’s try another calculation: what’s the time difference between 10:45 a.m. and 12:00 noon?

You should see in the sidebar that timeDifference.hour‘s value is 1 and timeDifference.minute‘s value is 15.

Date addition and subtraction

plus minus dice

If you’re writing some kind of reminder app, you might want to be able to let the user say “give me a reminder in 10 days”, which means you’ll need to calculate what the date and time will be 10 days from now. Since we’re doing date addition with only one unit, we can perform this calculation by using NSCalendar‘s dateByAddingUnit method:

dateByAddingUnit expects the following parameters:

  • unit: The type of unit to be added to the date. We want to add days, so we’re setting this value to NSCalendarUnit.DayCalendarUnit.
  • value: The number of units to be added to the date. We want to know what the date will be 10 days from now, so we set this to 10.
  • toDate: The date to which we’ll be adding units. We want to add 10 days to today, so we set this to a new NSDate (remember, instantiating an NSDate object without parameters creates an instance that refers to the current date and time).
  • options: In most cases, you’ll want to set this to nil.

I ran the code on January 28, 2015 at 11:29 p.m., so the resulting date stored in tenDaysFromNow is displayed in my playground’s sidebar as Feb 7, 2015, 11:29 PM.

I wanted to know what day of the week it would be 10 days from now, and which weekday of the month (the first, second, third…?) so I used the version of NSCalendar‘s components method that takes a single date and use it to extract the weekday and weekdayOrdinal components from tenDaysFromNow. At the time I ran the code, tenDaysFromNowComponents.weekday‘s value was 7 (Saturday) and tenDaysFromNowComponents.weekdayOrdinal‘s value was 1 (meaning that it’s the first Saturday of the month).

Here’s another calculation: what was the date and time 3 days, 10 hours, 42 minutes, and 5 seconds ago? We’re doing date arithmetic with more than one kind of unit — days, hours, minutes, and seconds — so we need NSCalendar‘s dateByAddingComponents method instead:

dateByAddingComponents expects the following parameters:

  • comps: the date components that we want to add to the given date. Note that since we’re performing date subtraction, all the components are expressed as negative numbers.
  • toDate: The date from which we’ll be adding (or in this case, subtracting). We want to subtract from the current date and time, so we set this to a new NSDate object instantiated without parameters (which, as I’ve said before, gives an instance representing the current date and time).
  • options: In most cases, you’ll want to set this to nil.

I ran the code on January 28, 2015 at 11:52 p.m., so the resulting date stored in then is displayed in my playground’s sidebar as Jan 25, 2015, 1:10 PM.

In closing

In this article, we covered:

  • Comparing two dates to see which one is the earlier on and which is the later one,
  • finding out how far apart two dates are, and
  • adding and subtracting from dates.

In the next installment, we’ll a closer look at date calculations and see some convenience methods that make date and time calculations simpler.

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Apple’s astonishing quarter

the most profitable quarter ever
Yesterday, which also happened to be the fifth anniversary of Steve Jobs’ iPad announcement…

Apple posted the financial results for their fiscal first quarter of 2015, in which they made a net profit of $18 billion. That’s not just a record for Apple, but for any company, any time in human history. The previous record-holder was the Russian firm Gazprom, the world’s largest extractor of natural gas.

The insanely popular iPhone 6 and 6 Plus carried the company, who sold nearly 75 million iPhones (in previous quarters, they had yet to surpass the 60 million mark, never mind 70 million), a 46% increase from the same quarter in the preceding year. “Greater China” — Apple’s term for the area comprising mainland China, Hong Kong, and Taiwan — helped push Apple over the top. They accounted for $16 billion of the nearly $75 billion revenue for Q1 2015.

This success in China comes at a cost to Samsung, whose market share in the Middle Kingdom is dropping. There’s a good summary of this situation in Bloomberg Business’ article, Apple Learns What Samsung Forgot: How to Sell Phones in China.

If there’s a cloud in all this silver lining, it’s iPad sales, which dropped to 21.4 million, a decrease of 21% year over year. In Wired’s article, How the iPad Went From Massive to ‘Meh’ in 5 Short Years, it’s noted that the iPad lives in that zone between smartphone and laptop, a gap that’s being closed by larger phones and thinner, lighter laptops.

Samsung: Speaking of earnings reports…

samsung q4 2014 report
Samsung will release its 4Q 2014 earnings report on Thursday morning in Seoul (in the UTC+0900 time zone, 14 hours ahead of North America’s Eastern Time), before markets open. According to the Wall Street Journal, here’s what we should expect:

  • Net profit: 4.5 trillion won ($4.2 billion)
  • Revenue: 52 trillion won ($48.3 billion)
  • Mobile: operating profit down 65% from the same time during the previous year, shipped 10 million fewer units as well
  • Chips: a 40% rise in profit, and increased production of mobile processors for both their devices and Apple’s

BlackBerry’s modest proposal

blackberry free market
In a recent post on BlackBerry’s blog, CEO John Chen talks about net neutrality and carrier neutrality, and what he says sounds sane and sensible. He then follows with application/content neutrality, and that’s where things get a little weird:

Unlike BlackBerry, which allows iPhone users to download and use our BBM service, Apple does not allow BlackBerry or Android users to download Apple’s iMessage messaging service. Netflix, which has forcefully advocated for carrier neutrality, has discriminated against BlackBerry customers by refusing to make its streaming movie service available to them. Many other applications providers similarly offer service only to iPhone and Android users. This dynamic has created a two-tiered wireless broadband ecosystem, in which iPhone and Android users are able to access far more content and applications than customers using devices running other operating systems. These are precisely the sort of discriminatory practices that neutrality advocates have criticized at the carrier level.

Therefore, neutrality must be mandated at the application and content layer if we truly want a free, open and non-discriminatory internet. All wireless broadband customers must have the ability to access any lawful applications and content they choose, and applications/content providers must be prohibited from discriminating based on the customer’s mobile operating system.

In other words, “Developers and online services like Netflix should be mandated by law to build BlackBerry apps,” apparently forgetting that in better BlackBerry-dominated times, BBM was a BlackBerry-only service and a competitive advantage.

PC World’s Jared Newman does a great job of explaining why Chen is wrong when it comes to “app neutrality”:

On some level, Chen’s position is understandable. The point of net neutrality is to encourage innovation in online services, and to prevent Internet providers from picking winners and losers. Chen is saying that BlackBerry hasn’t been given a fair shot because app makers have declared iOS and Android victorious.

But there’s a critical difference between net neutrality and the app neutrality that Chen proposes: With net neutrality, non-discrimination is the default. The Internet stops being neutral only if Internet providers create new, discriminatory practices such as blocking, throttling and fast lanes. The point of net neutrality rules is to maintain the Internet in its non-discriminatory state.

With Chen’s proposal of app neutrality, no such non-discriminatory state exists. Each new platform merely creates more work for developers, thereby requiring greater investment. Under Chen’s proposal, the barriers to entry for a small startup would become greater, and innovation would be stifled. App neutrality may be beneficial for BlackBerry, but it would actually counteract the things that net neutrality is trying to achieve.

Our guess is that Chen added “app neutrality” to his article on net neutrality as a way to attract more attention to it, generate discussion, and keep BlackBerry on people’s minds. Well played, sir.

At least it’s not as bad as tweeting BlackBerry promotional messages from an iPhone…

this article also appears in the GSG blog


How to work with dates and times in Swift, part one

by Joey deVilla on January 26, 2015

i just want to use dates

swift kickIf you’re just getting started with date and time programming in Swift, chances are that you probably did some Googling, found NSDate and its companion classes in Apple’s documentation and promptly got confused. Let me reassure you that it isn’t your fault. Apple’s Date and Time Programming Guide isn’t set up in the most helpful way, and its examples are in Objective-C, which can throw you off if you’re not familiar with its [instance method] calling syntax.

If you’re coming to Swift from JavaScript, which makes do with a single object type called Date, the idea of having this set of classes just to handle dates and times looks like overkill:

cocoa date time class chart

Click the chart to see it at full size.

This is the first article in a short series on programming dates and times in Swift. It’ll help you make sense of working with NSDate and its companion classes.

What is UTC? (or: “It’s 5 o’clock somewhere!”)

what time is it right now

People who like to drink are fond of saying “Well, it’s five o’clock somewhere!“, and it’s my favorite way of illustrating that what time it is depends on where you are. It’s why we have UTC — Coordinated Universal Time — the “One True Time” on which every other time zone is based. UTC replaced GMT (Greenwich Meridian Time, the time as observed at the Royal Observatory in Greenwich, London), and it doesn’t change for daylight savings. By having this standard, we eliminate the confusion that comes up when discussing times.

While most places have some names to refer to time zones in everyday conversation — such as Pacific, Mountain, Central, and Eastern in North America — the clearest way to indicate time zones is to express them as negative or positive offsets from UTC. For example, the North American time zone known as “Eastern” is 5 hours behind UTC, so it’s expressed as UTC-05:00. There are certain time zones where the offset isn’t whole hours, such as Newfoundland’s, which is UTC-03:30, and Nepal’s, which for some reason is UTC+05:45.

NSDate: Cocoa standard time

When you want to represent a date or time in Cocoa, you do so with an instance of the NSDate class. Here’s a nice, simple description of what NSDate is:


When you’re measuring time, you need a reference point. The Gregorian calendar — the one that I’m 99.999999% sure that you’re using right now — uses what is said to be the year of the birth of Christ as its reference point. Your age uses the date of your birth as a reference point. A time trial race uses the time at the start of the race as its reference point.

NSDate‘s reference point is the start of the third millennium: January 1, 2001 at midnight UTC. It stores time as an NSTimeInterval, a 64-bit floating point value representing a number of seconds. Negative values represent a number seconds before January 1, 2001, 00:00 UTC, and positive values represent a number seconds after that time. According to Apple’s documentation, this representation of time “yields sub-millisecond precision over a range of 10,000 years”, which means that an NSDate instance can represent any point in time from about 3000 BC/BCE to 7000 AD/CE.

Here are 4 historical dates, as seen from NSDate‘s perspective:

historical dates nsdate style

There are some consequences to the fact that NSDate treats time as an offset of seconds:

  • All NSDate values refer to both a date and a time. If you want to use an NSDate to store a date only, you ignore the time portion, and vice versa.
  • NSDate has no concept of time zones or any time unit other than seconds. That means you can’t ask it what year, month, day, hour, or minute correspond to the time it’s storing. As far as it’s concerned, there are no calendars; you work with NSDate‘s representation of time, when it’s time to display a date, time, or both, you format it to use the calendar and time zone that’s appropriate for the user.

There’s a method to this madness: it allows us to use and store dates and times in a way that’s independent of calendar systems, time zones, languages, and date formats. As I write this, it’s the year 2015 in the Gregorian calendar, but the Buddhist calendar says it’s 2558, and if you go by the Hebrew Calendar, it’s 5775. I may say it’s 9:45 a.m. as I write this in Tampa, but if you’re in California, it’s 6:45, and if you’re a soldier, you might call it 14:45 Zulu Time. I call the current month January, but you might call it Enero or Janvier. It’s all the same as far as NSDate is concerned, which makes it incredibly flexible.

Creating NSDates without any helper classes: now is easy, other dates ain’t so pretty

Let’s create some NSDates right now. Fire up Xcode, open a new playground, and enter the following code so that it looks like this:

You should see results in the sidebar that look similar to this:

playground 1

If you create an NSDate without any parameters, you get an instance representing the date and time at the moment it was created. That’s what we’ve done by creating the instance named now.

Note that in the sidebar beside line 5, where we created now, the result displayed in the sidebar is Jan 19, 2015, 8:52 AM. While the internal representation of the current time is a 64-bit floating point value, Xcode’s doing us a favor by representing it in a more readable format and using the local time zone. It’s doing this by making use of a date formatter, which we’ll cover later.

In line 6, we’re using the println function to display the default string representation of an NSDate, which is a completely numeric one. It’s more readable than a 64-bit floating point value, but it might not be in the format or time zone (or even the calendar system) that you want. Once again, this output comes courtesy of a date formatter.

Finally, in line 7, we use the timeIntervalSinceReferenceDate property to display now‘s internal representation of the date and time it’s storing: about 443 million seconds after January 1, 2001 at midnight UTC.

Let’s create the dates from the Historical dates, NSDate style picture above. Enter or paste the highlighted code below so that your playground looks like this:

In the sidebar, you should see nicely-formatted dates beside the NSDates you created.

NSDate has four initializers for creating specified dates and times:

Initializer Description
init(timeIntervalSinceReferenceDate:) Create an NSDate instance representing a time specified by a number of seconds before or after January 1, 2001 00:00 UTC.
init(timeIntervalSinceNow:) Create an NSDate instance representing a time specified by a number of seconds before or after the current date and time.
init(timeIntervalSince1970:) Create an NSDate instance representing a time specified by a number of seconds before or after January 1, 1970 00:00 UTC. This method exists not because Apple’s founders were California hippies nostalgic for the era of their youth, but for compatibility with Unix time.
init(timeInterval:sinceDate:) Create an NSDate instance representing a time specified by a number of seconds before or after a given NSDate.

You’ve probably noticed that none of these initializers lets you create an NSDate by giving it something convenient like a year, month, day, time zone and so on. Luckily, there are classes that will help us do this.

Creating NSDates with the help of NSCalendar and NSDateComponents

If you’re like most people, you’d probably much rather initialize a date object using a day, month, year, and time instead of some number of seconds before and after midnight on January 1, 1970, January 1, 2001, or any other arbitrary date. For this, we’ll need a couple of additional classes:

nscalendar and nsdatecomponents

First, there’s the NSCalendar class, which among other things, gives us a context for converting NSDate‘s “seconds before or after the third millennium” measurements into a familiar time system with years, months, days, hours, and minutes, and it accounts for time zones as well. Most of the time, the date and time system will be the Gregorian calendar, but iOS also lets you choose from 15 other calendar systems, including Hebrew and Buddhist.

Next, there’s the NSDateComponents class, which is an assembly of properties that make up a date, such as year, month, date, hour, minute, second, and so on. An NSDateComponents instance can be used to represent either:

  • A specific point in time, or
  • a duration of time.

To create an NSDate by specifying things like a year, month, day, and time, we’ll do the following:

  • Create an NSCalendar instance pointing to the user’s calendar
  • Specify a date using an NSDateComponents instance
  • Create the NSDate by passing the NSDateComponents instance to NSCalendar‘s dateFromComponents instance method

nsdatecomponents to nsdate

Let’s go back to our playground and create our first historical date: that of Alexander Graham Bell’s first phone call. We know it took place on March 10, 1876. While we don’t know the exact time it happened, we do know that it happened in North America’s Eastern time zone, as opposed to something like Kiritimati, a.k.a. Christmas Island. That place is 19 hours ahead and would’ve resulted in historians recording that day as March 11th rather than the 10th.

Enter or paste the highlighted code below so that your playground looks like this:

Any calendar, regardless of its time zone, to turn date components into dates using its calendar system. If you specify a time zone in the date components, it will take that time zone into account; if you don’t specify one, the date will be created using the calendar’s time zone. We created an instance of the user’s calendar, which incorporates the user’s local and time zone settings, because it’ll be useful later when we want to go in the opposite direction and convert dates into date components.

Note that after setting the year, month, and day properties of firstLandPhoneCallComponents, we set the timeZone component using the preferred initializer, init(name:), which lets you specify a time zone by any of the standard string identifiers listed in the tz database of time zones. I could’ve used one of the city names such as America/New_York (or for those of you familiar with Canada, America/Toronto, America/MontrealAmerica/Atikokan, or America/Pangnirtung) to specify the Eastern time zone. It’s far clearer — especially to people not from the U.S. — to use the time zone names that begin with US or Canada, such as US/Eastern, US/Central, US/Mountain, and US/Pacific rather than city names.

Once we’ve set up the date components, we use the calendar’s dateFromComponents instance method to convert them into a date. I’m in the US/Eastern time zone, the same one as the one specified in the date components, so the result in the sidebar beside this line of code shows as “Mar 10, 1876, 12:00 AM” (we didn’t specify a time in the date components, so the resulting date has the default time of 00:00). The date displayed in the sidebar uses your system settings, which may be different from mine.

Let’s enter the other three historic dates. Enter or paste the highlighted code below so that your playground looks like this:

Note that we used different time zones for the “Stevenotes”. Both took place at the same time, 10:00 a.m. Pacific, but we set the time for the iPhone announcement as 1:00 p.m. US/Eastern, and the time for the iPad announcement as 10:00 a.m. US/Pacific. Both results in the sidebar appear at the same time; on my machine, they appear as Jan 27, 2010, 1:00 PM.

dateFromComponents works with what you give it

Suppose we want to create a date just by specifying that it’s 11:00 a.m. on the first Saturday of March 2015 in the US/Eastern time zone. Here’s how it’s done:

NSDateComponentsweekday property lets you specify a weekday numerically. In Cocoa’s Gregorian calendar, the first day is Sunday, and is represented by the value 1. Monday is represented by 2, Tuesday is represented by 3, all the way to Saturday, which is represented by 7.

The weekdayOrdinal property lets you specify which specified weekday of the month. By setting weekday to 7, we’re specifying a Saturday; by then setting weekdayOrdinal to 1, we’re specifying the first Saturday of the month.

Here’s another example, where we get the date for the Thursday on the 18th week of 2015:

The other way around: getting NSDateComponents from NSDates

Right now, your playground should look like this, with a number of dates being created from date components:

Now it’s time to go the other way around, and extract date components from those dates. Once again, it’s the calendar that provides the method for making the conversion.

To extract NSDateComponents from an NSDate, we’ll do the following:

  • Create NSCalendar instances, if needed
  • Specify a set of date components using NSCalendarUnit bitmasks
  • Create the NSDateComponents by passing the NSDate instance to NSCalendar‘s components instance method

nsdate to nsdatecomponents

We already have a calendar instance: userCalendar, which is associated with the user’s time zone. If we use it to extract date components from a given date, the dates and times will be interpreted in the context of its time zone.

Let’s create two more calendars with two different time zones:

  • The US/Pacific time zone (UTC-08:00)
  • The Japan time zone (UTC+09:00)

Here’s what the code looks like:

Extracting all the possible date components from a date can be computationally costly, so NSCalendar‘s components instance method requires you to build a bitmask specifying the components you want to extract by ORing together NSCalendarUnit values. We want to extract these components from our dates:

  • year
  • month
  • day
  • hour
  • minute
  • weekday
  • weekdayOrdinal

Here’s the code:

Now that we’ve done that, we can start extracting date components:

In your playground’s sidebar, you should see results similar to those listed in the table below:

Component My user calendar Pacific calendar Japan calendar
year 2007 2007 2007
month 1 1 1
day 9 9 10
hour 13 10 3
minute 0 0 0
weekday 3 3 4
weekdayOrdinal 2 2 2

As you can see, January 9, 2007 at 10:00 a.m. in the US/Pacific time zone is January 9, 2007 at 1:00 p.m. in my time zone (US/Eastern) and January 10, 2007 at 3:00 a.m. in Japan. In the US, that date was the second Tuesday in January 2007; in Japan, it was the second Wednesday.

Turning dates into strings (and vice versa) with NSDateFormatter

nsdate - nsdateformatter - stringJust as you use an calendar to convert date components into dates and vice versa, you use a date formatter — an instance of the NSDateFormatter — to do the conversions.

Formatting date strings for the user

If you need to display a date as text for the user, it’s best if you use Cocoa’s built-in date styles. These are a set of predefined styles for formatting dates and times based on the user’s preferred settings. These styles, which are all values of the NSDateFormatterStyle enumeration, come in a selection of lengths — short, medium, long, and full — and using them is the preferred way to create date strings for the user to read.

Add the following code to your playground:

Here’s how the various date and time formatter styles get rendered:

If dateStyle and timeStyle are both set to… the date formatter’s output looks like…
ShortStyle 1/27/10, 1:00 PM
MediumStyle Jan 27, 2010, 1:00:00 PM
LongStyle January 27, 2010 at 1:00:00 PM EST
FullStyle Wednesday, January 27, 2010 at 1:00:00 PM Eastern Standard Time

What’s up with NoStyle? It’s there so you can limit the resulting string so that it shows only the date or only the time.

NSDateFormatter has a timeZone property so that you can ensure that the date string reflects a specific time zone:

Formatting date strings for other computers

As I wrote earlier, if you’re formatting dates for the user, it’s strongly recommended that you use NSDateFormatter‘s dateStyle and timeStyle properties, which will format dates and times according to the user’s settings. However, if you need to need your date strings to be in a specific format (for an API, for example), you can provide NSDateFormatter with a format string:

While you can browse through Appendix F of the Unicode Technical Standard #35 to look at all the date format specifiers supported by NSDateFormatter, you might find it easier to use the table below. It shows a number of format strings applied to the iPhone announcement date (January 9, 2007 at 10:00 a.m. Pacific):

Format string Result
'Year: 'y' Month: 'M' Day: 'd Year: 2007 Month: 1 Day: 9
MM/dd/yy 01/09/07
MMM dd, yyyy Jan 09, 2007
E MMM dd, yyyy Tue Jan 09, 2007
EEEE, MMMM dd, yyyy' at 'h:mm a. Tuesday, January 09, 2007 at 10:00 AM.
EEEE, MMMM dd, yyyy' at 'h:mm a zzzz. Tuesday, January 09, 2007 at 10:00 AM Pacific Standard Time.

Turning strings into dates

If you specify a date format string, you can use NSDateFormatter to take a string following that format to turn it into an NSDate. For example:

Tying it all together

If you’ve made it to this point in the article, this chart should now make sense:

cocoa date time class chart

Once again, click the chart to see it at full size.

You should now be able to:

  • Create dates “from scratch” (that is, create them using an offset of a number of  seconds from the start of the third millennium)
  • Create dates from date components (that is, from numbers representing a day, month, and year)
  • Convert between dates and date components
  • Convert dates into string representations and string representations of dates into dates

In the next article in this series, we’ll look at date calculations and some handy functions that let you harness Swift’s expressive power and make working with dates easier.


If someone walked up to you on the street and asked you what your password was, would you say?

The TV show Jimmy Kimmel Live sent an interviewer out on the street to ask (presumably) random people on Hollywood Boulevard what their passwords were. As you might expect, they showed only those people who gave away their passwords (and of that group, only those who signed a release form to appear on the show), but the fact that anyone did so shows that we’ve got a big security problem, and it’s us. A couple of them simply gave them away without question, while a couple of others has to be conned — very easily — into divulging.

This is the technologist’s nightmare. For all the security measures we put into our applications and devices, they can easily be undone by the users. That’s why I often make use of this cartoon when talking about security:

and in this corner we have dave

The article also appears in my personal blog, The Adventures of Accordion Guy in the 21st Century.


SWIFTly rising up the programming language charts

by Joey deVilla on January 16, 2015

swift on redmonk

Click the graph to see it at full size.

For a programming language that came out in beta in June, Swift’s rise in popularity is quite impressive. Stephen O’Grady writes in his report on Redmonk’s Programming Languages Rankings for Q1 2015, while most of the rankings stayed stable, Swift’s meteoric rise from 68th place in Q3 2014 to its present number 22 spot stands out.

As with any programming language popularity ranking system, Redmonk’s rankings are determined by looking at the online “trail” left by programming language users. Their system uses two key metrics:

  • Discussion of the language on Stack Overflow, where discussions are tagged with language names, and
  • Projects posted on GitHub, where projects are tagged with language names.

O’Grady writes:

During our last rankings, Swift was listed as the language to watch – an obvious choice given its status as the Apple-anointed successor to the #10 language on our list, Objective-C. Being officially sanctioned as the future standard for iOS applications everywhere was obviously going to lead to growth. As was said during the Q3 rankings which marked its debut, “Swift is a language that is going to be a lot more popular, and very soon.” Even so, the growth that Swift experienced is essentially unprecedented in the history of these rankings. When we see dramatic growth from a language it typically has jumped somewhere between 5 and 10 spots, and the closer the language gets to the Top 20 or within it, the more difficult growth is to come by. And yet Swift has gone from our 68th ranked language during Q3 to number 22 this quarter, a jump of 46 spots. From its position far down on the board, Swift now finds itself one spot behind Coffeescript and just ahead of Lua. As the plot suggests, Swift’s growth is more obvious on StackOverflow than GitHub, where the most active Swift repositories are either educational or infrastructure in nature, but even so the growth has been remarkable. Given this dramatic ascension, it seems reasonable to expect that the Q3 rankings this year will see Swift as a Top 20 language.

The other well-known ranking of programming language popularity, the TIOBE Index, puts Swift at the number 25 position in its January 2015 edition. They just named JavaScript as the 2014 language of the year, but as they observed:

It was a close finish. Swift and R appeared to be the main candidates for the title but due to a deep fall of Objective-C this month, a lot of other languages took advantage of this and surpassed these two candidates at the last moment.

Another interesting way to gauge a programming language’s popularity is to count the Swift courses and the number of students on Udemy. As of this writing, there are 53 Swift courses in English, and another 18 in other languages. Three of these courses have 10,000 students or more, the most popular of which is Rob Percival’s The Complete iOS and Swift Course: Learn by Building 15 Real-World Apps. It has over 53,000 students, who’ve paid as much as $199 (that’s the standard price, but there are often sales where you can sign up for much, much less).

If you’re the sort to try to read the tea leaves of programming language popularity to see what the Really Big Deals this year will be, keep an eye on what I’m calling the “Three M’s”: mobile, modelling data, and massive data. The TIOBE folks seem to agree with this assessment:

It is always tempting to try to forecast what will change in 2015. Objective-C will probably lose its dominant position in mobile app development, whereas Java and Swift will gain traction in that field. Java might even become number one of the TIOBE index again. Other trends in progamming are modelling and big data. Here, MATLAB and R appear to be the market leaders. There is a realistic chance that they will enter the top 10 in 2015.


The book 'Beginning iPhone Development with Swift'As I wrote in an earlier article, I’ve been working my way through Apress’ Beginning iPhone Development with Swiftan iOS 8/Swift-flavored update of Beginning iOS 7 Development. The original book was released in March 2014, the iOS 8 and Swift betas came out that June, the GM versions came out in September, and the revised book was released in mid-November. In the eight-month span between the original book and the revision, the authors didn’t have much time to try out iOS 8 and Swift, never mind do the rewrite, and as a result, they ended up with a few errors in their text, as well as leaving out some useful material.

I also wrote in that earlier article that in spite of these problems, I still think it’s a good book (as do some other people; it’s got 5 stars on Amazon as of this writing), and where some may see errors and oversights, I see opportunities.

Here’s another opportunity that came up…

The date picker exercise

Chapter 7 of Beginning iPhone Development with Swift, Tab Bars and Pickers, has you build a multi-view app where you use all kinds of “picker” controls. The first view you work on is one with a date picker; here’s a screen shot:

iOS app showing a date picker and a button labelled 'Select'. The selected date in the date picker is 'Today, 4:20 PM'

In this simple view, you use the picker to select a date, tap the Select button, and you’re presented with an alert that looks like this:

iOS app with date picker and button, overlaid with an alert showing the selected date as '2015-01-14 21:20:13 +0000'

Note the format of the date displayed in the alert:

  • It’s not formatted in the most readable way.
  • It has too high a level of detail. The user didn’t enter the number of seconds or a time offset.
  • I entered the time in my time zone (4:20 p.m., Eastern Standard Time, or GMT-5), but the alert is displaying the time for GMT.

Here’s what the book had to say about this:

The date picker does not allow you to specify seconds or a time zone. The alert displays the time with seconds and in Greenwich Mean Time (GMT). We could have added some code to simplify the string displayed in the alert, but isn’t this chapter long enough already? If you’re interested in customizing the formatting of the date, take a look at the NSDateFormatter class.

I’d much rather have the alert look like this…

iOS app with date picker and button, overlaid with an alert showing the selected date as 'Wednesday, January 14, 2015 at 4:20 PM'

…but they’d left doing so as an exercise for the reader. Let’s go through this exercise, shall we?

The original code

Here’s what the view looks like in the Storyboard:

datepicker view

And here’s the code for buttonPressed in the corresponding view controller:

In this code, we’re simply taking the value from the date picker’s date property and using its string representation in the string constant message. In iOS, dates are represented by instances of the NSDate class, which is all about representing a single point in time. While it has the date property for access the date stored within, it doesn’t have any members for formatting that date.

Enter NSDateFormatter

iOS has a number of formatter classes, whose job is to take data and convert it into a text representation, typically for the benefit of the user. These classes have names that end with the word Formatter and are subclasses of the abstract class NSFormatter. You can find out more about these classes in NSHipster’s excellent overview.

The book pointed us towards NSDateFormatter, a class that serves two purposes:

  • Converting NSDate objects into string representations, and
  • Converting strings into NSDate objects.

NSDateFormatter has a class method called localizedStringFromDate that does what we want. Given the following:

  • An NSDate instance,
  • A style specifying how we want the date part of the NSDate instance formatted, and
  • A style specifying how we want the time part of the NSDate instance formatted

…it returns a string representing the NSDate instance in the format we specified.

We specify the styles for the date and time using values from the NSDateFormatterStyle enum, which has the following values:

  • NoStyle: Unstyled.
  • ShortStyle: Typically numeric-only, such as 1/14/15 and 4:20 PM.
  • MediumStyle: A medium-length style, using abbreviations. Examples are Jan 14, 2015 and 4:20:00 PM.
  • LongStyle: A longer style with full text. Examples are January 14, 2015 and 4:20:00 PM EST.
  • FullStyle: Full style with complete details. Examples are Wednesday, January 14, 2015 and 4:20:00 PM Eastern Standard Time.

For our code, we’ll use FullStyle for the date and ShortStyle for the time. Here’s what the revised code looks like — the highlighted lines show the new or modified code:

This code gives us the date in a more user-friendly format.

This example scratches the surface of what’s possible with NSDateFormatter. You should take a look at Date Formatters, which is part of a larger section of their documentation called Data Formatting Guide.

You might also want to check out: How to program an iOS text field that takes only numeric input with a maximum length


tomi ahonen - mobile pundit

Tomi Ahonen, Nokia executive during its heyday, mobile consultant to Fortune 500 companies, prolific author, and all-round mobile curmudgeon, has published his predictions for the mobile handset industry in 2015 on his blog, Communities Dominate Brands. The title of his article, So the Smartphone ‘Bloodbath’ Annual Preview for Year 2015 – This is so boring, gives you a taste of his writing style: a little hyperbole, and a lot of stream of consciousness. It’s a big, monolithic block of text, chock-a-block with the asides that are his stock in trade, and it’s a lot to wade through.

We’ve taken Ahonen’s article and distilled it for what we think are the big take-aways from his 2015 predictions. As always, this sort of future-telling should always be taken with a grain of salt — while he often has brilliant insights into mobile tech (it’s why we read what he has to say), he’s been known to be oh-so-very-wrong from time to time (as everyone is).


Samsung’s sitting pretty as the world’s largest handset maker, at almost twice the size of the next runner-up, and larger than the 2nd- and 3rd-place vendors combined. They’re also the largest of the “major handset makers who genuinely cater to the global mass market” (as opposed to Apple, who are aimed at the higher-end customer, or BlackBerry, whose focus is the enterprise). Their “everywhere” status means that they’ll make good money and stable, but it also means that investors can’t count on them to be as “ridiculously profitable” as Apple.

samsung galaxy k zoom

Samsung’s weakness, according to Ahonen, is their sales management, which he describes as “a total disaster”. They produce a confusing array of all-too-similar models, and fail to highlight interesting and innovative devices like the Galaxy K Zoom, which reimagines the smartphone as a camera with a great lens and 10x optical zoom that just happens to have a phone rather than the other way around, priced 20% below the latest iPhone model. Given that:

  • most people’s phones are their cameras these days,
  • we can’t post enough photos on Facebook, Twitter, Instagram, and SnapChat, and
  • camera quality is a big factor in many people’s smartphone choices,

you’d think that this would be a heavily-marketed, big-selling Android phone. But just try to find it at your local store.

samsung tizen

Tizen, Samsung’s troubled, often-delayed device operating system that they they hope will free them from dependency on Google and Android, is expected to debut at this year’s CES, where it’ll debut on its TV sets. While the Tizen Alliance — a rag-tag group of a dozen hardware manufacturers who’ve promised to release Tizen-powered devices — seens to have fizzled out, Ahonen still believes that Samsung’s market size and clout, combined with the sort of effort and execution Samsung can make when they’re doing things right, mean that Tizen could be a game-changer over the next couple of years.


apple and ios

Apple has historically been one of Ahonen’s blind spots. Back when Nokia, Motorola, RIM, and Palm were the ones to beat, he consistently downplayed Apple. Later, as Nokia was going down in flames, his thesis was that the iPhone didn’t kill Nokia, Nokia’s response to the iPhone did.

apple watch

Ahonen’s prediction that we should start to see the final transformation of Apple into a niche OS and out of the mass market as Android assumes the position for mobile devices that Windows had for desktop computers. As for the Apple Watch, he says that yes, the iFaithful will line up to buy it, but in the end, even they will reject it in the long run.



They did well for themselves in the laptop world by buying an internationally-recognized and respected brand — IBM’s ThinkPad — and turning it into a profitable business. It appears that they’re trying to repeat history now that they own the Motorola marque. Buying these brands are smart moves, says Ahonen, allowing them to sidestep the reputation of “cheap Chinese” that other vendors like Huawei and ZTE have to contend with, especially given the rave reviews their most recent phones have received. Moto, and not Xiaomi, is the biggest threat to Samsung, according to Ahonen.



Here’s the Ahonen take in a single sentence: They won, and the only way they can lose is if they themselves screw it up.

The “Next Five” (Coolpad, Huawei, TCL, Xiaomi, ZTE)

the next five

Here in the U.S., none of these brands — Coolpad, Huawei (“WAH-way”), TCL, Xiaome (“SHOW-mee”, the first syllable rhymes with “cow”), and ZTE — are household names, but in Ahonen’s list, they’re the next runners-up after the top three smartphone vendors (Xiaomi recently moved up to the number 3 position). Xiaomi is getting a lot of press right now, partly because of its dramatic growth, and partly because they’re hardcore Apple copycats.

If he had to bet on members of the “next five”, Ahonen would put his money on Huawei and ZTE, because selling phones requires more than product, but also relationships with carriers worldwide. Huawei and ZTE have been selling telecom equipment to the carriers for years, so they have an “in” that upstarts like Xiaomi don’t.

Legacy brands (such as HTC, LG, and Sony)


Ahonen doesn’t see these vendors — HTC, LG, and Sony — making much of a mark. He says that while they may see the occasional quarter where they see “record profits” (or have moments in the sun, as LG seems to be having with well-reviewed phones like their G3), these will be fleeting moments followed by “obsolescent models are overflowing in the showrooms then there are returns to the factory and suddenly huge losses generated”. “The brand and sales channel,” he argues, “is of far more value to one of the rising stars (mostly from China) who want to take over the world than to a legacy manufacturer who suddenly sees big losses.”



“One of the saddest stories in tech,” says Ahonen. He says that the Passport and Classic missed the mark, and that while they may find a home catering to the enterprise, either as a hardware vendor or as a pure software play, they’ll never return back to the top 10. They’re even slipping out of the top 20 right now.

Microsoft (the company formerly known as Nokia)


Just as he has a bit of a blind spot for Apple, Ahonen has a sore spot about Windows Phone. He can’t talk about it without seething with rage, and especially at the Microsoft exec-turned Nokia CEO-turned Microsoft exec Stephen Elop. We’ll condense his four paragraphs on this topic to:

  • They’re soooo dead. We still have no idea why 1/3 of Lumia phones haven’t been activated!
  • Microsoft can’t kill off their smartphone business now. The best thing they can do is fire the current Windows Phone executive VP of Devices and Services (Elop) and let some hapless, well-intentioned patsy run it into the ground.
  • Expect them to ditch the phone hardware division sometime in the next three years.

The other mobile OSs

firefox sailfish ubuntu

The short version: They don’t stand a chance.

The Company still known as Nokia

real nokia

Microsoft may have bought Nokia’s handset business, but they didn’t buy the entire company. There’s still a company called Nokia that makes networking equipment for carriers, mobile mapping and navigation technologies, and even mobile devices. Right now, they’re contractually forbidden from making smartphones under their own brand for another year or so, but they’ve put out a well-reviewed tablet. Ahonen believes that with their relationships with carriers and the right execution, Nokia could make an Android-powered comeback. As a bonus, he follows this with a (long, so very, very long) “Hollywood scenario” in which Nokia’s ability to turn dying businesses around (as they did with Siemens’ telecom and Motorola’s networking divisions) and the brand loyalty they’ve earned worldwide make it surpass Apple and become Samsung’s biggest rival. It reads like fan fiction, and even he admits that it’s a very unlikely scenario.

this article also appears in the GSG blog