UIViewController doesn't update view's constraints when the device orientation is changing

Question

I'm making an app where the iPad can be used in both landscape and portrait mode. The configuration of my UIViewControllers is the following :

I have a UIViewController with a UICollectionView which has the following constraints : top, leading, trailing, and bottom set to 0 with its superview (the superview is the UIView of my UIViewController ).

When I tap a cell, I push another UIViewController in the UINavigationController which is a detail viewController of the cell. Simple.

When I change the device orientation in the first view controller, the UICollectionView bounds are set properly.

Here come my problem :

If I select a cell in the UICollectionView , the second detail viewController is displayed. Then if in this second ViewController I change the device orientation and then I go back into the first viewController, the view of my UIViewController hasn't been rotated. I don't know why, I tried this without success :

self.view.layoutIfNeeded() in viewDidAppear() of my firstViewController to update constraints according the current orientation, it didn't work. This didn't work because I noticed one thing :

The frame view of my first viewController is still the same as the previous orientation, it didn't change... But if I rotate again the device, the UIViewController detect the orientation changes, and the view bounds are set properly.

So my problem is : when I'm in the second view controller, and that I'm rotating the device, and then that I go back in the previous view controller, the previous controller hasn't detected the orientation change I just made in the second view controller.

GIF Demo :

After that I made a rotation from portrait to landscape mode, the view is not changed as the debug view hierarchy tool shows below :

The UIView is still in portrait, so the UICollectionView constraint's can't be updated with the new orientation...

Any ideas?

Answer 1

Resolved by resetting the frame of the view in my first viewController with the screen bounds in the viewWillAppear method :

public override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(true)
    self.view.frame = UIScreen.main.bounds
    self.view.layoutIfNeeded()
}

Like that the main UIView of my viewController have the right frame, and the constraints can be updated automatically when I call layoutIfNeeded() on my UIView.

Answer 2

Found need to reset the frame size of collectionview. add self.collectionview.frame.size = size

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {

    if let layout = self.collectionview.collectionViewLayout as? UICollectionViewFlowLayout {
        let width = (size.width - 30) / 3
        layout.itemSize = CGSize(width:width, height:width)
        self.collectionview.frame.size = size
        layout.invalidateLayout()
    }
}