Reset offset, onTapGesture works, but onRotated does not work, why? - rotation

Question

I want the view containing 2 rectangles floating in the bottom of the screen, whatever the orientation is portrait or landscape.
code is a test, when orientationDidChangeNotification happened, I Found UIDevice.current.orientation.isPortrait and UIScreen.main.bounds.height often have wrong value, why?
Anyway, test code is just reset offset = 0 in onRotated(). but it doesn't work; otherwise onTapGesture works fine.
Q1: Is it a wrong way for SwiftUI? SceneDelegate.orientationDidChangeNotification -> contentView.onRotated()?
Q2: why do UIDevice.current.orientation.isPortrait and UIScreen.main.bounds.height often have wrong value?
Q3: How to let a view float at the bottom of screen in both portrait and landscape?
let height: CGFloat = 100
struct TestView: View {
#State var offset = (UIScreen.main.bounds.height - height) / 2
var body: some View {
ZStack {
Text("+")
VStack(spacing: 0) {
Rectangle().fill(Color.blue)
Rectangle().fill(Color.red)
}
.frame(width: 100, height: height)
.offset(y: offset)
.onTapGesture {
self.offset = 0
}
}
}
func onRotated() {
// let isPortrait = UIDevice.current.orientation.isPortrait
offset = 0//(UIScreen.main.bounds.height - height) / 2
// print("\(isPortrait), screen height = \(UIScreen.main.bounds.height)")
}
}
class SceneDelegate: UIResponder, UIWindowSceneDelegate {
var window: UIWindow?
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
let contentView = TestView()
if let windowScene = scene as? UIWindowScene {
NotificationCenter.default.addObserver(forName: UIDevice.orientationDidChangeNotification, object: nil, queue: nil) { notification in
contentView.onRotated()
}
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: contentView)
self.window = window
window.makeKeyAndVisible()
}
}
...
}

Answer 1

contentView is not a reference, it is a value, so you call .onRotated on own copy of contentView value that lives only within callback
let contentView = TestView()
if let windowScene = scene as? UIWindowScene {
NotificationCenter.default.addObserver(forName: UIDevice.orientationDidChangeNotification, object: nil, queue: nil) { notification in
contentView.onRotated() // local copy!!!
}
instead create listener for notification publisher inside TestView, so it can change self internally.
Moreover, it is not clear the intention but SwiftUI gives possibility to track size classes via EnvironmentValues.horizontalSizeClass and EnvironmentValues.verticalSizeClass which are automatically changed on device orientation, so it is possible to make your view layout depending on those environment values even w/o notification.
See here good example on how to use size classes