Get a notification with viewWillAppear - in another VC? - ios

Question

Say you have
var someVC: UIViewController
is it possible to essentially do the following, somehow?
get a notification when {
someVC has a viewWillAppear
self.#selector(wow)
}
#objc func wow() {
print("we spied on that view controller, and it just willAppeared"
}
Is that possible ?
(Or maybe on didLayoutSubviews ?)
(I realize, obviously, you can do this by adding a line of code to the UIViewController in question. That's obvious. I'm asking if we can "add on" to it from elsewhere.)

Answer 1

If I understand your question correctly, you want ViewController B to receive a notification when viewWillAppear is called in ViewController A? You could do this through the Notifications framework. Keep in mind that both VC's have to be loaded for one to receive a notification.
Alternatively, if the two VC's are on the screen at the same time, then I'd recommend a delegate pattern - have VC A tell an overarcing controller class that it's viewWillAppear has been called, and this overarcing controller will then inform ViewController B.
To do this using Notifications:
(This is from memory, so please excuse typos)
class TestClassA: UIViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
// To improve this code, you'd pull out the Notification name and perhaps put it into an extension, instead of hardcoding it here and elsewhere.
NotificationCenter.default.post(Notification.init(name: Notification.Name.init(rawValue: "viewControllerAppeared")))
}
}
class TestClassB: UIViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(viewControllerAppeared(notification:)), name: Notification.Name.init(rawValue: "viewControllerAppeared"), object: nil)
}
#objc func viewControllerAppeared(notification: NSNotification) {
print("other viewcontroller appeared")
}
}
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