So before I write part 2 of the story of how my first mobile(iOS) app came to be, this would be a small post on how to use Extensions in Swift, to make code more readable...amongst other things.
Problem
So in my iOS app, there are a few places where I have to get the day before(yesterday) and the day after(tomorrow) for a date.
Solution
In the first version of my code, I had the code such as this (Read on to find out a more correct solution for calculating dates)
For the day after
let oneDay:Double = 60 * 60 * 24
return self.dateByAddingTimeInterval(oneDay)
For the day before
let oneDay:Double = 60 * 60 * 24
return self.dateByAddingTimeInterval(-(Double(oneDay)))
one day has 24 hours, each hour has 60 mins and each minute has 60 seconds, so 60 * 60 * 24
to calculate the solution to my problem. This was working and it was all fine...until I delved deeper into Swift(by reading this ebook by Apple) and found out about Extensions!!! It was love at first write? (if there is such a thing) Extensions in Swift are awesome and you can have a read about the benefits of it here or follow this tutorial.
Great! I am now in love with Extensions in Swift, but how does it help me?
Ok so using extension, all I need to do is add the following code in one of the Swift files in my iOS app project
extension NSDate {
var dayAfter:NSDate {
let oneDay:Double = 60 * 60 * 24
return self.dateByAddingTimeInterval(oneDay)
}
var dayBefore:NSDate {
let oneDay:Double = 60 * 60 * 24
return self.dateByAddingTimeInterval(-(Double(oneDay)))
}
}
and, if I have an NSDate anywhere in my project, I can just find out the dayBefore or the dayAfter the NSDate object like this
let today = NSDate()
today.dayBefore
today.dayAfter
Awesome right?
The most correct solution for calculating dates (for iOS8)
Ok, so the main point of this post was really more about me yelling out how much I love Extensions in Swift. However since I have used date calculations as an example and similar logic exists in my app's code, I should make this right and include the correct solution.
Now since writing this post i.e. one day ago, I started looking around a bit to find out how other's are going about solving this problem. During my search, I came across this post and realised one problem with the above date calculations. Here's a quote from Rob's answer in the post, indicating one problem with it,
"But I would advise against doing any manual adjustments of
NSDate values by adjusting it by some time interval that is a multiple of the seconds per day (e.g. 24*60*60). That technique works fine if you're just adding some time interval, but for date calculations, you really want to use NSCalendar, to avoid problems stemming from daylight savings and the like." - Rob
So the code in this post to calculate dayBefore and dayAfter for the Extension on NSDate, should be something like the the code below. Please note that the code below would only work on iOS8 and above, so if you have a device running an earlier iOS version, it is not going to work.
extension NSDate {
var dayAfter:NSDate {
let calendar = NSCalendar(calendarIdentifier: NSGregorianCalendar)!
return calendar.dateByAddingUnit(.CalendarUnitDay, value: 1, toDate: self, options: nil)!
}
var dayBefore:NSDate {
let calendar = NSCalendar(calendarIdentifier: NSGregorianCalendar)!
return calendar.dateByAddingUnit(.CalendarUnitDay, value: -1, toDate: self, options: nil)!
}
}
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