Making a simple toggle button with UIButton

It’s actually pretty straightforward to turn a UIButton into a toggle button. (checkbox, switch, whatever you prefer to call it!)

We can make use of the isSelected property that UIButton inherits from UIControl. All we need to do is connect a ‘Touch Up Inside’ action to the UIButton, that toggles this property:

@IBAction func toggleButton(_ sender: UIButton) {

Pretty easy right? Just like that, our button now toggles between the ‘Default’ and ‘Selected’ Control States. We can customize how these states look in the attributes inspector for the button.

Here I have customized a button to display either a tick or cross, depending on whether it’s selected, using SFSymbols ‘’ and ‘’:

This seems to work pretty well, except for one minor detail. When the user has their finger down on the button, the button defaults to the ‘Default’ state (although darker). This works ok for the ‘unselected’ state, but doesn’t look quite right for the ‘selected’ state:

No Highlighted state selected.

How can we modify this state? If you open the ‘State Config’ combo box, you’ll find another state called ‘Highlighted’:

In UIButton this state refers to the state the button is in while the user’s finger is on it. Great! So we can modify the Image for this state too in the Attributes Inspector. Here I’m setting the image for the ‘Highlighted’ state to ‘’:

Testing this out on the app, we see that this didn’t actually help us much! Sure, our ‘Default’ state has a neat ‘Highlighted’ state now, but our ‘Selected’ state still is defaulting to the ‘Default’ state when the user holds their finger down on the button:

What we need is to define the state for both ‘Selected’ AND ‘Highlighted’. Unfortunately that isn’t possible in the storyboard, but fortunately for us, we can do it in code. Just set up an @IBOutlet for your button, and then set the button’s image for this state in the viewDidLoad method. Here I am setting the image to ‘’ if the button is selected and the user holds their finger down on the button:

@IBOutlet weak var button: UIButton!
override func viewDidLoad() {
  button.setImage(UIImage(systemName: ""), 
                  for: [.highlighted, .selected])

Finally! If we test the app now the button’s states should now be much more intuitive:


So — here again are the steps to creating a simple toggle button:

  1. Customize the button(for example, its image) in the attributes inspector of the storyboard for three states — ‘Default’ (off), ‘Highlighted’ (over) and ‘Selected’ (on).
  2. Connect the button to an IBOutlet so that you can set up a fourth state (a combination of ‘Highlighted’ and ‘Selected’) in the viewDidLoad method:
button.setImage(UIImage(systemName: ""), 
                  for: [.highlighted, .selected])

3. Connect the button to an IBAction that actually performs the toggling:

@IBAction func toggleButton(_ sender: UIButton) {

That’s it! Your button should work.

A reusable toggle button subclass

Of course, if you prefer you could set up a subclass of UIButton that handles the toggle operation for you:

import UIKit
class ToggleButton: UIButton {
  @IBInspectable var highlightedSelectedImage:UIImage?
  override func awakeFromNib() {
    self.addTarget(self, action: #selector(btnClicked(_:)), 
                   for: .touchUpInside)
                  for: [.highlighted, .selected])
  @objc func btnClicked (_ sender:UIButton) {

This subclass contains an inspectable property highlightedSelectedImage that you can use to specify the image to display in the elusive fourth state (‘Selected’ and ‘Highlighted’) that is otherwise not available in the attributes inspector.

Connecting your button to this subclass in the identity inspector, you can now completely set up your toggle button in the storyboard. Hooray!👍


Tagged with: ,
Posted in Swift

Tiling a background image – sans code!

I recently wrote an article on a simple custom UIView class you can use to tile an image. Unfortunately – this doesn’t help us in a LaunchScreen, where custom classes are not allowed. Fortunately – there’s another way to tile an image, it’s pretty straightforward, and it doesn’t require a single line of code!

Step 1 – Bring in your image to tile into the Assets Catalog, then select Editor > Show Slicing.Screenshot 2019-11-12 14.51.47.png

Step 2 – The 1x, 2x and 3x options will disappear, and you will need to select Start Slicing.

Screenshot 2019-11-12 14.52.19.png

Step 3 – You will have the option to slice horizontally, vertically or both:

Screenshot 2019-11-12 14.52.27.png

Xcode will assume you want to slice the image in the center.

Screenshot 2019-11-12 14.52.32.png

This will stretch the center part of your image, something like this:

Screenshot 2019-11-12 15.03.47.png

This isn’t what you want!

Here are the defaults Xcode chose when I opted to slice my image: (you can find these in the Attributes Inspector for the image – and don’t forget, we’re still in the Assets Catalog)

Screenshot 2019-11-12 14.52.44.png

Step 4 – We need to set the Left, Right, Top and Bottom to 0, and the Width and Height of the Tiles to the width and height of the image. Something like this:

Screenshot 2019-11-12 14.53.05.png

Step 5 – Now, back in the Storyboard, we can add a UIImageView, and in the Attributes Inspector, make sure Content Mode is set to Scale To Fill:

Screenshot 2019-11-12 14.54.03.png

And there, like magic, the image in our image view will tile, and it works in the LaunchScreen storyboard too, hooray!

Screenshot 2019-11-12 14.54.08.png

Tagged with: ,
Posted in Swift

Tiled background image in custom UIView class

Sometimes you need a repeated or tiled image in your app, often for a background. Something like these rain-drops for example:

Here’s a simple UIView subclass that accepts an image parameter, and renders a repeated tiled image, even in the storyboard:

It creates a patterned image in a UIColor object, sets this as the current fill, and then fills the view’s rect with this color.

Here’s how it looks in the storyboard:

Tagged with: ,
Posted in Swift

Presentation Style default in iOS 13

This week is International Week of the Deaf, so to thank the community that have been a big part of my app Subtitles Viewer‘s success, Subtitles Viewer PRO is free for the whole week. Coincidentally, and perhaps unfortunately, iOS 13 is also brand spanking newly released this week, so just when the app is getting substantial downloads, some teething issues have presented themselves with the new release. Grrr…

Now I know Apple liked large navigation bars from iOS 11, but these navigation bars looked extra large. What’s worse, I found that after building the app in Xcode 11, when I swipe down, the whole app disappeared, leaving behind just the title screen!

Strange! I took a look at the good old capture view hierarchy and discovered a transition view peeking up above the navigation controller. Hmm, the plot thickens…

Screenshot 2019-09-26 16.33.48.png

What’s going on? It turns out this was all related to a change in default presentation style.

Blink and you’ll miss it – in the WWDC State of the Union 2019, this was announced:

Another component of iOS 13’s new look is cards. Since the original SDK, the default presentation style on iPhone has covered the full screen. We’re changing that default to a much more fluid card presentation. Cards provide a visual stack so you can see at a glance that you’re in a presentation. And even better, they’re dismissible with just a single downward swipe.

Screenshot 2019-09-26 23.22.05.png

So previously segues would always default to a presentation style of ‘Full screen’, exhibit a:

Now, presentations on the iPhone default to what Apple are calling ‘cards’, exhibit b:

Note that after presenting the view controller as a card, you can swipe it down to remove it.

In practice, what has happened is that the default presentation style is ‘automatic’ which in iOS 13 is interpreted by UIViewController as ‘Page Sheet’. The documentation for UIModalPresentationStyle.automatic describes this: “For most view controllers, UIKit maps this style to the UIModalPresentationStyle.pageSheet style”.

This new feature could work well in some UX design, but in Subtitles Viewer, when the intro animation is complete it automatically segues to the rest of the app. Swiping down to see the intro animation again was definitely unwanted in this case.

What to do about it? Turns out the solution is simple. If you select the presenting view controller in the storyboard and select Attributes Inspector, you’ll find the Presentation attribute is probably set to Automatic. Change this Full Screen, and you’re done, problem solved!


Tagged with: , ,
Posted in Swift

Property Wrappers and User Defaults

I love magical new features that help us abstract away boiler-plate code and let us focus on the unique features of our apps. Property wrappers is such a feature, and seriously – it just feels like magic!


Let’s take a look at an example to see how property wrappers work.

User defaults: Level 1

A reminder, the simplest way user defaults would work is to first set up some sort of a key:

enum Keys { //enum to prevent instantiation
  static let beenHereBefore = "Been Here Before"

You could then use this to store or retrieve the user default:

//Retrieve user default:
if !UserDefaults.standard.bool(forKey: Keys.beenHereBefore) {
  //Onboarding could go here for example
//Store user default:
UserDefaults.standard.set(true, forKey: Keys.beenHereBefore)

Great! But wouldn’t it be nicer if we could just set and retrieve the property without worrying about the underlying user defaults implementation?

User defaults: Level 2

Instead, let’s abstract away the User defaults code into a GlobalSettings type:

//Retrieve user default:
if !GlobalSettings.beenHereBefore {
  //Onboarding could go here for example
//Store user default:
GlobalSettings.beenHereBefore = true

Much more readable, right?

But of course, we now need to set up the GlobalSettings type:

enum GlobalSettings { //enum to prevent instantiation
    enum Keys {
        static let beenHereBefore = "Been Here Before"
    static var beenHereBefore:Bool {
        get {
            return UserDefaults.standard.bool(forKey: Keys.beenHereBefore)
        set {
            UserDefaults.standard.set(newValue, forKey: Keys.beenHereBefore)

Now that’s fine for one user default, but what if we have several? We would have to duplicate this code defining a key and setting and retrieving the UserDefaults for each property.
Could we abstract this code even further? Well, here’s where we can see the magic of property wrappers!

Screenshot 2019-09-02 21.01.33

User defaults: Boss Level! (using Property Wrappers)

A property wrapper is a special attribute you can create and apply to a property that automatically runs a bunch of code behind the scenes for the property.

Let’s move the User Defaults get and set code to a property wrapper.
*Disclaimer: the code for Persist is based on sample code in the Swift Evolution proposal for Property Wrappers, proposal 258.

Let’s give the property wrapper the name Persist:

struct Persist<T> {
  let key: String
  let defaultValue: T

  var wrappedValue: T {
    get {
      return UserDefaults.standard.object(forKey: key) as? T ?? defaultValue
    set {
      UserDefaults.standard.set(newValue, forKey: key)

To define the property wrapper we follow three essential steps:

1. Create a type (in this case, a struct). The name of our type becomes the name of the property wrapper.
2. Prefix the type with the @propertyWrapper attribute.
3. Include a ​wrappedValue property. In this case this a generic property wrapper, so the wrappedValue property is defined as a generic. To perform an action when this property is retrieved or stored, it is defined as a computed property with both a getter and a setter.

In this case, as UserDefaults needs a key to store and retrieve a property, a key property has been defined in the Persist struct.

As the property wrapper is defined as generic, it uses UserDefault‘s generic object method to retrieve a user default. As this method returns an optional, the Persist struct also defines a defaultValue property that will be returned if the value returned by the object method is nil.

Of course, as Persist is a struct, it doesn’t need an initializer specifically defined to intialize these two properties, as a memberwise initializer will be automatically generated.

Now, we can adjust our GlobalSettings type to use the property wrapper:

enum GlobalSettings {
  @Persist(key: "BeenHereBefore", defaultValue: false)
  static var beenHereBefore: Bool

Holy moly. You can see how much shorter the declaration of the beenHereBefore property is, now that all of the UserDefaults code has been abstracted to our custom property wrapper Persist.

All we did to add our custom property wrapper was to prefix a variable with an at symbol (@) followed by the name of the wrapper (Persist), followed by any initialization required.
Like magic, the property wrapper code we wrote will now execute for this variable!

We could easily add a bunch of user defaults to our GlobalSettings type, with minimal additional lines of code.

enum GlobalSettings {
  @Persist(key: "BeenHereBefore", defaultValue: false)
  static var beenHereBefore: Bool
  @Persist(key: "TopScore", defaultValue: 0)
  static var topScore: Int
  @Persist(key: "UserName", defaultValue: "Anon")
  static var userName: String

As all the code dealing with persisting data is now in our Persist property wrapper, if we wanted to make adjustments to how this works, we would only have to make this change in one place. Let’s say we change our mind and decide to use iCloud’s NSUbiquitousKeyStore container to persist our data, instead of UserDefaults. Making this change would be straight-forward:

struct Persist {
  let key: String
  let defaultValue: T

  var wrappedValue: T {
    get {
        return NSUbiquitousKeyValueStore.default.object(forKey: key) as? T ?? defaultValue
    set {
        NSUbiquitousKeyValueStore.default.set(newValue, forKey: key)

As I mentioned, you can read more about property wrappers in Swift Evolution proposal 258. You can also see more about it in WWDC video Modern Swift API Design. Just be cautious, back then wrappedValue was simply known as value. (it was renamed 8 days after the talk – ooh that would be frustrating!)

Enjoy playing with property wrappers, let me know what magical property wrappers you create!

Tagged with: ,
Posted in Swift

SF Symbols in iOS 13

I was playing with the amazing SwiftUI with Apple’s tutorials (stay tuned, I hope to write something on SwiftUI soon) when I noticed something interesting:

Screen Shot 2019-06-06 at 8.55.02 pm.png

Where does this “star.fill” come from, I wondered… There’s no “star.fill” in the asset catalog?! It turns out the clue was in the initializer parameter “systemName”.

So from iOS 13, UIImage can now be initialized with systemName, which generates a “system symbol image”.  What are these “system symbol images”? Well, Apple has provided a program called “SF Symbols” that lets you browse all 1,500+ of them! You can download the program at their Apple Design Resources page.

Screen Shot 2019-06-07 at 9.16.15 am.png

Here are just some of the SF Symbols!

And it couldn’t be easier to use:

Screen Shot 2019-06-06 at 11.33.39 pm.png

There is a WWDC session on SF symbols well worth checking out here. You’ll also find Apple’s guidelines for using SF Symbols in the Human Interface Guidelines here. You’ll also find guidance there for building your own SF Symbol, using the SF Symbols program.

In the SF Symbols program you’ll notice you can play with the weight and scale of the image. You’ll find an example of these in the Human Interface Guidelines:


You can adjust the weight and scale of the image, along with its pointSize, using a config property:

Screen Shot 2019-06-06 at 11.44.22 pm.png

It should be noted that pointSize refers to a typographical point size – the same point size a font uses – rather than points on the screen.

Why have both pointSize and scale, you might ask. Well, the scale property allows you to adjust the scale of a symbol in relation to the text around it without having to adjust the pointSize. Perhaps you might be lining up an image with a label, adding an image to a button, or even inserting an SF symbol in a string! It should be mentioned that inserting an SF symbol into a string isn’t working yet for the current beta of Xcode 11, but it sounds very promising, adjusting the style of the symbol to the text surrounding it!

Having point size available is great, but we generally try to avoid specifying a point size with text — instead we prefer to use text styles, such as Body, Headline, etc where possible to take advantage of dynamic type. This is possible with SF symbols too — instead of specifying the point size, you can create the config property using a text style, just as you might with a label or text field:

Screen Shot 2019-06-07 at 1.18.28 pm.png

By the way, so far we’ve been looking at how to add SF symbols in code. We also saw at the start of this post that you can also include SF symbols in SwiftUI views.You might be interested to know you can also add them in the storyboard:

Screen Shot 2019-06-07 at 12.08.55 pm.png

Of course, as we saw at the start of this post, you can also include SF symbols in SwiftUI views.

Well, that’s the basics – there’s a lot more to look at – such as alignment, automatic configuration based on size class, making your app with SF symbols compatible with devices with < iOS 13, and building your own SF symbols. Again, I recommend you check out the WWDC session on SF symbols here.

In conclusion I think this is a really welcome addition to Xcode/iOS – apps will have a more consistent look across iOS, and I think SF symbols should make life much easier for us – less time for example, taken up sourcing icons and finding (or designing) a variety of sizes and weights. What do you think?

Tagged with: , , , ,
Posted in Swift

Swift 5 – it’s alive!

its-alive.jpgIt’s been a couple of weeks now since Swift 5 has arrived, with a bunch of features, such as:

  • ABI stability
  • source compatibility
  • isMultiple – a fancy technique for checking if a number is a multiple of another number.
  • Dictionary compactMapValues – finally we can properly compactMap a dictionary!
  • Result type – handle results from aynchronous code in a much cleaner way.
  • Raw strings – again Swift has had some enhancement to handling Strings.
  • And more!

If you want to a refresher on one or more of these features, I go into them in detail in a new Medium post, you can check it out here.

Tagged with:
Posted in Swift

Optionals in Swift explained – with a cat in a box!

If you’ve come to Swift from a language that doesn’t use optionals, you might find the concept a little strange and the syntax unfamiliar at first. Sometimes it helps to learn the unfamiliar with something familiar – in my lightning tour of optionals, I explain optionals with a cat in a box!

So – imagine you have a box:


Inside the box you know you have one of two things – either no cat…


…or a cat!


What you have just imagined, is a Cat optional!


As you can see, you declare an optional with the data type of its contents (Cat in this example), followed by a question mark:

var cat:Cat?

But now that we have a Cat optional, how do we get at its contents – or put another way – how do we unwrap the box?

Check my lightning tour of Optionals to find out:

Tagged with:
Posted in Swift

Get a continent from longitude-latitude

For a project I’m working on I needed to know if a point (latitude,longitude) was in a continent, and if so, which one!

To do this, first I set up a Continent enum to work with, making it a String (to easily print) and CaseIterable (to iterate through the cases later):

enum Continent:String,CaseIterable {

    case australia
    case northAmerica
    case southAmerica
    case africa
    case europe
    case asia
    case antarctica

I found this stackoverflow post, which though it wasn’t written in Swift, gave some very general polygons that vaguely encompassed the seven continents, exactly what I needed:


I first set up a utility method to convert a latitude and longitude array into a GMSMutablePath. (I’m going to solve this using the Google Maps SDK)

I then used the polygons from the StackOverflow post and converted the Latitude and Longitude arrays into paths in static variables in the Continent enum:

Great! Now seeing if a point is inside a polygon is as simple as comparing a CLLocationCoordinate2D property with a GMSMutablePath property, and you can do that with the GMSGeometryContainsLocation function.

I set up a contains function in the enum that checks if a continent contains the point:

func contains(point:CLLocationCoordinate2D)->Bool {
    switch self {
    case .australia:
        return GMSGeometryContainsLocation(point, Continent.australiaPath, true)
    case .northAmerica:
        return GMSGeometryContainsLocation(point, Continent.northAmericaPath, true) ||
            GMSGeometryContainsLocation(point, Continent.northAmerica2Path, true)
    case .southAmerica:
        return GMSGeometryContainsLocation(point, Continent.southAmericaPath, true)
    case .africa:
        return GMSGeometryContainsLocation(point, Continent.africaPath, true)
    case .europe:
        return GMSGeometryContainsLocation(point, Continent.europePath, true)
    case .asia:
        return GMSGeometryContainsLocation(point, Continent.asiaPath, true) || GMSGeometryContainsLocation(point, Continent.asia2Path, true)
    case .antarctica:
        return GMSGeometryContainsLocation(point, Continent.antarcticaPath, true)

North America and Asia both have two have polgyons that represent their areas.

So now, to determine which continent contains a point, all we have to do is iterate through the cases of the Continent enum, calling the contains method. I set up a getContinent method to do this:

static func getContinent(at point:CLLocationCoordinate2D)->Continent? {
    for continent in Continent.allCases {
        if continent.contains(point: point) {
            return continent
    return nil

To see how this could be used, imagine you’ve set up a map view in a view controller, let’s call it MapViewController, and we’ve set the view controller as the map view’s delegate. You could set up the mapView:didTapAt method to be called when the user taps on the map. We could use the coordinate property passed into the method to determine which continent the user has tapped, simply by passing the coordinate property into the Continent.getContinent method:

extension TestMapViewController:GMSMapViewDelegate {
    func mapView(_ mapView: GMSMapView, didTapAt coordinate: CLLocationCoordinate2D) {
        if let continent = Continent.getContinent(at: coordinate) {
Tagged with: ,
Posted in Swift

Getting the keyboard height

Some time ago I answered a question in StackOverflow comparing the keyboard height on the iPhone X and the iPhone 8:

I got these heights by:
1. Adding an observer of the UIResponder.keyboardWillShowNotification notification:

NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow), name: UIResponder.keyboardWillShowNotification, object: nil)

(In fact, if we want all keyboard frame changes, we should probably be observing the keyboardWillChangeFrameNotification notification, I discuss this in my book.)

2. Adding the selector function to be called:

@objc func keyboardWillShow(_ notification: NSNotification) {

3. Then, within this function, we need to dig down a crazy chain of downcasts and optional unwrapping from the userInfo dictionary to extract the height out of the notification object:

if let keyboardRect = (notification.userInfo?[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue)?.cgRectValue {

Done! We have the keyboard height.

The person I was answering on StackOverflow was trying to display a view directly above the keyboard, and was confused about why it wasn’t displaying in the correct place. (I believe there was some confusion because of the safe area inset on the iPhone X.)

To illustrate that displaying the view was possible, I set up a red rectangle directly above the keyboard. I was recently asked on Twitter how I did this:

Well, pretty straightforward, actually. Now we have the keyboardRect, all I had to do was set up a CGRect just above it, convert that to a CAShapeLayer, give it a strokeColor and lineWidth, and add it to the view’s layer.

      let newRect = CGRect(x: 0, y: view.frame.height - keyboardRect.height - 100, width: keyboardRect.width, height: 100)
      let rectLayer = CAShapeLayer()
      rectLayer.path = CGPath(rect: newRect, transform: nil)
      rectLayer.strokeColor =
      rectLayer.lineWidth = 5
Tagged with:
Posted in Swift