How to remove passed closure from UIViewController - ios

Question

sorry maybe title not so much informative, so here is my problem
I want to create ThemeManager and apply to all screens, theme can be changed in the app, thats why I added closureList which will fire and update all related screens
class ThemeManager {
static let shared = ThemeManager()
private(set) var theme: Theme
private var bindedList: [()->Void] = []
private init () {
self.theme = AppGreenTheme()
}
func apply(theme: Theme) {
self.theme = theme
}
func bind(closure: #escaping ()->Void) {
bindedList.append(closure)
}
func bindAndFire(closure: #escaping ()->Void) {
bind(closure: closure)
closure()
}
}
here is how I want to use it from any UIViewController, or any UIView
ThemeManager.shared.bindAndFire {
// here I will get theme changes and update my screen
}
so I wanted to know, in this case will I create reference cycle for UIViewController, or UIView, and which is the best approach to remove closures from the list after parent UIViewController or UIView, will be removed from memory.

Answer 1

Its safe as long as you pass your UIViewController as a weak reference, like so
ThemeManager.shared.bindAndFire { [weak self] in
guard let strongSelf = self else { return }
// here I will get theme changes and update my screen
}
But NotificationCenter is better approach for this to rely on, here is basic ThemeManager example
class ThemeManager {
static let shared = ThemeManager()
static let NotificationName = NSNotification.Name("Notifacation.ThemeManager")
var theme: Theme!
func switchTheme(_ theme: Theme) {
self.theme = theme
NotificationCenter.default.post(name: ThemeManager.NotificationName, object: self.theme)
}
}
Usage:
class ViewController: UIViewController {
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(themeDidUpdate(_:)), name: ThemeManager.NotificationName, object: nil)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NotificationCenter.default.removeObserver(self)
}
#objc func themeDidUpdate(_ notification: Notification) {
guard let theme = notification.object as? Theme else { return }
// here I will get theme changes and update my screen
}
}
Update-2 Example NotificationCenter with a closure
NotificationCenter.default.addObserver(forName: ThemeManager.NotificationName, object: nil, queue: OperationQueue.main) { [weak self] (notification) in
guard let strongSelf = self, let theme = notification.object as? Theme else { return }
// here I will get theme changes and update my screen
}

Answer 2

You can wrap the closures with a struct that has also has a property you can check for equality and return the value of that property when a closure is added. The view controller can then pass this id if it wants to remove the closure.You can hide the wrapper from the rest of the code. You can also use UUID if you don't want to keep track of some counter. You can also use a dictionary to store the closure with the id as the key.
class ThemeManager {
private var counter = 0
private var closures: [ClosureWrapper] = []
private struct ClosureWrapper {
let id: Int
let closure: () -> Void
}
func bind(closure: #escaping () -> Void) -> Int {
counter += 1
let wrapper = ClosureWrapper(id: counter, closure: closure)
closures.append(wrapper)
return wrapper.id
}
func removeClosure(with id: Int) {
guard let index = closures.firstIndex(where: { $0.id == id }) else {
return
}
closures.remove(at: index)
}
}
Here's version where you don't need to keep track of an id for the closure. It uses NSMapTable with weak keys to store the closures. You can pass the view controller as the key and when it is deallocated the passed closure will be automatically removed from the map table.
class ThemeManager {
private let closureTable = NSMapTable<NSObject, ClosureWrapper>(keyOptions: .weakMemory, valueOptions: .strongMemory)
private class ClosureWrapper {
let closure: () -> Void
init(closure: #escaping () -> Void) {
self.closure = closure
}
}
func bind(from source: NSObject, closure: #escaping () -> Void) {
let wrapper = ClosureWrapper(closure: closure)
closureTable.setObject(wrapper, forKey: source)
}
func callClosures() {
for key in closureTable.keyEnumerator().allObjects {
let wrapper = closureTable.object(forKey: key as? NSObject)
wrapper?.closure()
}
}
}