SwiftUI - Updating a Page View Controller with a new page - ios

Question

I'm building a weather app that is hosted on a public repo here.
The most important files for this issue are the PageView and the RepresentedPageViewController.
I've created a UIPageViewController that interfaces with SwiftUI via UIViewControllerRepresentable. It allows a user to swipe through different cities and see each city's weather data, much like Apple's Weather app. When the makeUIViewController method of my page view controller is called I set its view controllers (there are 3 in this case to begin with, where each represents a city):
pageViewController.setViewControllers([controllers[0]],
direction: .forward,
animated: false)
This works fine and I'm able to navigate (swipe) between the different pages.
In the app's search menu, a user can then tap on a new city that they want to get the weather for. This adds the new city to the app's datasource of cities that the page view controller uses to create a page for each city.
Because the data object that holds the cities is stateful, the UI is recomputed when that object is set (when a user adds a new city). This triggers the updateUIViewController method in the page view controller. In this method, I reset the page view controller's viewcontrollers (there are now 4 because the user has added a new city):
func updateUIViewController(_ uiViewController: UIPageViewController, context: UIViewControllerRepresentableContext<RepresentedPageViewController>) {
// Check that the view controllers of the page view controller need to be reset.
// This is true when a user has added a new city because we'll create a new
// view controller to be added to the page view controller. We perform this check because
// we don't want to reset the viewcontrollers in all cases where the updateUIViewController method is called.
if shouldResetControllers {
uiViewController.setViewControllers([controllers[0]],
direction: .forward,
animated: false)
shouldResetControllers = false
}
}
My issue is that once this is done, the user is only able to see the first city of the viewcontrollers. The page view controller is still there because the user is still able to swipe, but there is only one city (the first one). I've created a screen recording of the result which you can view here.

Answer 1

think the problem stays in the Coordinator:
when you update controllers in pageviewcontroller, the parent property of Coordinator remains the same (and because it is a struct, all his properties). So you can simply add this line of code in your updateUIViewController method:
context.coordinator.parent = self
also, remember that animation of pageViewController.setViewControllers will occur, so you have to set animated to false, or handle it properly.
There are many other ways to solve this (I wrote the most intuitive solution),
the important thing is to know where the error comes from.

Answer 2

It seems like this is a SwiftUI bug. I had a similar problem where a UI update would reload the PageViewController with a single ViewController.
Adding an id to the PageViewController, described in "Updating an #Environment to pass data to PageViewController in SwiftUI results in loss of swiping between ViewControllers", seems to work.