Swift good practices, interesting things to know about iOS

3 years after


You'll find there some good practices/hints I think are very relevant and that was good for me : They can come from people I worked with, from courses/tutorials I followed, and also from others guidelines and good practices authors.

Table of Contents

Interesting things to know about

Xcode UI Testing

Wait for an object to appear if animations

At the beginning, I encountered issues when checking if a particular button is hittable or not, simply because it was faded in ( animation ) and so not directly present in the view. One interesting solution I found is this one :

let enableButton = app.buttons[NSLocalizedString("Enable", comment: "foo")]
expectationForPredicate(NSPredicate(format: "hittable == true"), evaluatedWithObject: enableButton, handler: nil)
waitForExpectationsWithTimeout(3, handler: nil)

It'll wait for 3 seconds until the predicate is true (in our case, the button is hittable, so until the button appear). After the elapsed time, of it's not true, it'll execute the XCTAssert hittable == true.

Tap at specific coordinates

Runtime Attribute Storyboard

Clicking on the text button redirect me another view, and clicking on the square check it.

What I wanted to do was just checking the button, so just tapping on the little square on the left. I did it with :

 let checkButtonCoordinate = app.buttons["CGUButton"].coordinateWithNormalizedOffset(CGVector(dx: 0, dy: 0))

Global and local variable observers

You can add variable observers in any types of variable, even Global and local.

Let's see an example :

 var numberOfPerson = 0 {
   didSet {
    // Do something

 class Person {
   var name = "Anonyme" {
     didSet {
       // Do something else

   func showResume() {
     var resume: String? {
       didSet {
         // Do what you need to do

     // ...

User Defined Runtime Attribute

You can use the from your storyboard to init some properties of your object instead of doing it programmatically.

So, you can for example, replace :

  self.debtView.layer.maskToBounds = true
  self.debtView.layer.cornerRadius = 5.0


Runtime Attribute Storyboard

Good practices in Swift and iOS

Native Swift struct initializers

Use the native Swift struct initializers rather than use CGGeometry functions.

So replace :

 let myButton = UIButton(frame: CGRectMake(0.0, 0.0, self.bounds.width / 2, self.bounds.height))


 let myButton = UIButton(frame: CGRect(x: 0.0, y: 0.0, width: self.bounds.width / 2, height: self.bounds.height))

Because in Objective-c, we used to use CGRectMake to get a CGRect struct because for initializing a strut, it is necessary ( as in C if my memory is good ) to create first the structure, and then assigning value to variables. With Swift, struct have constructors with parameters, so no need to use external functions.

No need to remove observer

You don't need to remove observer in deinit function when iOS > 9.0 anymore

From Apple Documentation

In OS X 10.11 and iOS 9.0 NSNotificationCenter and NSDistributedNotificationCenter will no longer send notifications to registered observers that may be deallocated[...] This means that observers are not required to un-register in their deallocation method.

Range operator

To check if a number is between a range, don't do

if number >=0 && number <= 100

Use range and news operators instead :

 if 0...100 ~= number


Use extension when conforming to some protocol ( uitableview, printable, .. ) to keep a well organized code unless if that's its role.

 // MARK: - TableView Delegate -

 extension HomeViewController: UITableViewDataSource {

  func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return 5

  func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return 1

  // etc.

Tips for using let

Use let until Xcode yell so you can replace it with var

Typealias for a argument/return type

Use typealias when closures are referenced in multiple places

 typealias CoolClosure = (foo: Int) -> Bool

CGRect and negative values

When accessing the x, y, width, or height of a CGRect, prefer using rect.width, rect.minY, etc.. that are swift extension and that by default standardize values instead of direct struct member access. From Apple's CGGeometry reference:

All functions described in this reference that take CGRect data structures as inputs implicitly standardize those rectangles before calculating their results. For this reason, your applications should avoid directly reading and writing the data stored in the CGRect data structure. Instead, use the functions described here to manipulate rectangles and to retrieve their characteristics.

For example :

 let rect = CGRect(origin: CGPoint(x: 0.0, y: 0.0), size: CGSize(width: -40.0, height: -40.0))

 rect.size.width // return -40,  Not good, negative value
 rect.width      // return 40,  OK

 rect.origin.y   // return 0.0,  Not OK
 rect.minY       // return -40.0,  OK

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