Uipagecontroller
UIPageController
Intro
Adding VC as a scrollable VCs to swipe as the onboarding flow in iOS.
Usage
Overridden Methods Calls
UIKit lifecycle methods being subscribed.
In order to have this method be intercepted by UIKit -> UIViewController when you have overridden methods such as ViewWillTransition . You need to first add the content view controllers to the ViewController hierarchy.
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) { }
By using .addChild() method you would append the UIViewControllers to the view controller hierarchy - UIKit parsing overriden methods irrespective of the child views being rendered or not.
My teammates comment about the it
so configuring the page controller with the view controllers that it’s in charge of displaying add the content view controllers to the hierarchy. but we weren’t adding the page controller (itself a view controller container) to the view controller hierarchy, only its view to the view hierarchy. so adding the page controller to the view controller hierarchy automatically added all of it’s children to the view controller hierarchy.it’s exactly like appending an isolated tree as a subtree to a large tree.
NS Internal InconsistencyException
pageViewController setViewControllers crashes with "Invalid parameter not satisfying: [views count] == 3
This happens only when the code block isn't being called upon from Main thread or higher .qos for asynchronous code path execution.
SO | pageviewcontroller-setviewcontrollers-crashes-with-invalid-parameter-not-satisf
The solution according to the Stack Overflow thread is to make sure utilze GCD tools in order to switch the thread back to main thread for UI work.
dispatch_async on the main queue
dispatch_async(dispatch_get_main_queue(), ^ { });
DispatchQueue.main.async {
self.pageViewController?.setViewControllers()
}