Swift Cheat Sheet for Dates, Formatters, and Date Components

Thu, 26 May 2016 18:04:01 +0000

Working with NSDate, NSDateFormatter, and NSDateComponents can be a little convoluted, so I’ve created myself a cheat sheet that will be updated as I discover new tips and tricks in this realm.

The new cheat sheet can be found over at GitHub in the form of an Xcode Playground:

Resources

Swift Dates Cheat Sheet Playground

Topics that are included in the Playground are as follows:

Getting today’s date
Converting NSDate to String
Converting String to NSDate
Getting components of an NSDate
Setting components of an NSDate
Creating new NSDate instances from NSDateComponent instances

The best way to view this cheat sheet is by downloading the playground from GitHub, but here’s a straight copy-paste from the repo in case you just want to copy and paste it into a playground of your own from here:

 1import UIKit
 2
 3/*: 
 4# Overview
 5This is a cheat sheet for working with dates, date formatters, and date components.
 6
 7*/
 8
 9//: # Today's Date
10
11let today = NSDate()
12let thisTimeTomrrow = NSDate(timeIntervalSinceNow: 86400)
13let thisTimeYesterday = NSDate(timeIntervalSinceNow: -86400)
14
15/*: 
16# Date Formatting
17Working with NSDateFormatter to convert dates to stings and vice-versa
18*/
19
20//: ## Converting dates to strings
21let dateFormatter = NSDateFormatter()
22dateFormatter.dateFormat = "yyyy-MM-dd"
23
24print(dateFormatter.stringFromDate(today))
25
26dateFormatter.dateFormat = "MMM dd, yyyy"
27
28print(dateFormatter.stringFromDate(today))
29
30
31//: ## Converting strings to dates
32
33// Consider what might potentially come back from an API of some sort and set a dateFormatter's dateFormat property appropriately...
34
35dateFormatter.dateFormat = "yyyy-MM-dd"
36var stringFromApi = "2016-01-01"
37var date = dateFormatter.dateFromString(stringFromApi)
38
39stringFromApi = "May 26, 2016"
40date = dateFormatter.dateFromString(stringFromApi)
41
42/* Notice how the format set to the date formatter (yyyy-MM-dd) differs from the format that came back from the API (MMM dd, yyyy), which resulted in `date` being nil.
43*/
44
45/*:
46# Date Components
47Working with NSCalendar and NSCalendarUnit to work with components of dates.
48*/
49
50//: ## Getting date components
51var calendarUnitFlags: NSCalendarUnit = [.Year, .Month, .Day, .Hour, .Minute, .Second]
52var dateComponents = NSCalendar.currentCalendar().components(calendarUnitFlags, fromDate: NSDate())
53dateComponents.year
54dateComponents.month
55dateComponents.day
56dateComponents.hour
57dateComponents.minute
58dateComponents.second
59
60// Observe how leaving out .Hour, .Minute, and .Second affects the values of those components of a date:
61calendarUnitFlags = [.Year, .Month, .Day]
62dateComponents = NSCalendar.currentCalendar().components(calendarUnitFlags, fromDate: NSDate())
63dateComponents.year
64dateComponents.month
65dateComponents.day
66dateComponents.hour
67dateComponents.minute
68dateComponents.second
69
70//: ## Setting date component values
71
72dateComponents.year = dateComponents.year + 1
73dateComponents.month = 1
74dateComponents.day = 1
75dateComponents.hour = 0
76dateComponents.minute = 0
77dateComponents.second = 0
78
79//: ## Creating dates from components
80let newDate = NSCalendar.currentCalendar().dateFromComponents(dateComponents)

Date, Date?, and the ToString Method in VB.Net

Fri, 03 Oct 2014 17:28:05 +0000

I just spent the last 45 minutes frustrated as to why I was getting the following exception

“Input string was not in a correct format.” and “[InvalidCastException: Conversion from string “MMMM dd, yyyy” to type ‘Integer’ is not valid.]

I kept thinking to myself, “How hard can this possibly be?!! I’ve done this a thousand times — Why is it wanting to convert my format string into an Integer??! AAHHH!!”. Consulting MSDN on the matter only confirmed that I knew what I was doing with the string formatter.

What got me in the end is that it turns out I didn’t know what I was doing with my Date object. In fact, I wasn’t dealing with a Date object at all. I was dealing with a Date? object (that is, a Nullable(of Date). Date and Date? are not the same. And it matters, because the ToString() method of Date has _different overloads _than the ToString() method of Date?. Only the Date type allows you to put in a format string to fancy up how the date is displayed when it’s converted to a string.

My solution:

Wrap my Date? object instance in a CType, converting to type Date.
Call ToString() on the converted value:

CType(someObject.dateInstance, Date).ToString("MMMM dd, yyyy")

Sanity… recovered.

Date on Andrew Bancroft

Swift Cheat Sheet for Dates, Formatters, and Date Components

Date, Date?, and the ToString Method in VB.Net

My solution: