change all view controller background in swift - ios

Question

I am working on my project app where I want to allow my user to change the background wallpaper to be same on all screens. I have a settings screen where I am adding that. I have added ImageViews to all view controllers and I have some view controllers that have UIscrollview so I added Imageview to slides template. Now my dilemma is how can I allow the user to pick the preview wallpaper so it changes the Imageview image on every view controller. I already created such #IBOutlets as shown below.
#IBOutlet weak var slideBackground: UIImageView!
#IBOutlet weak var homeScreenBackground: UIImageView!
#IBOutlet weak var settingsBackground: UIImageView!

Answer 1

You should use the system wide NotificationCenter.
Simply put, you can have objects subscribe to the default NotificationCenter and specify a selector (method) to execute when a notification is posted.
You can also post custom notifications that represent the wallpaper change event.
I have used this in an app I built to achieve a system wide 'dark mode' transition.
To post:
#objc func postWallpaperChangeNotification() {
NotificationCenter.default.post(name: .wallpaperChanged, object: nil)
}
To subscribe:
NotificationCenter.default.addObserver(self, selector: #selector(someMethodToRunWhenWallpaperChanges(_:)), name: . wallpaperChanged, object: nil)
You also need to remove the observer in deinit().
This is approximate code to give you a flavour, any questions hmu.

Answer 2

You have a few options.. what option is best depends on your needs really.
As Woodstock mentioned in his answer, you could use NotificationCentre, I wont re-explain that.
Another option would be to store the image name in UserDefaults that you are going to use for the background image.
any time you change the background... set the value
UserDefaults.standard.set(imageName, forKey "backgroundImageName")
Then in each view controller, just load the value on viewWillAppear
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated: animated)
if let backgroundImageName = UserDefaults.standard.string(forKey: "backgroundImageName") {
self.backgroundImageView.image = UIImage(named: backgroundImageName)
}
}
Both of these options are not very easy to unit test though. You could use Mocks to test it.
A bonus of this method is that it will 'remember' the setting inbetween the user restarting the app.
An example of how you might reduce code repetition using subclassing:
class WallpaperedViewController: UIViewController {
lazy private var imageView: UIImageView = {
let imageView = UIImageView()
view.addSubview(imageView)
view.sendSubview(toBack: imageView)
return imageView
}()
private func setWallPaperImage() {
let imageName = UserDefaults.standard.string(forKey: "backgroundImageName")
let image = UIImage(named: imageName!)
imageView.image = image
//imageView.contentMode = .scaleAspectFill
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
imageView.leftAnchor.constraint(equalTo: view.leftAnchor).isActive = true
imageView.rightAnchor.constraint(equalTo: view.rightAnchor).isActive = true
imageView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
self.setWallPaperImage()
}
}
Then for each ViewController that has this background image wallpaper just extend this class:
class SomeViewController: WallpaperedViewController {}