An example of animateCollectionViews, a method to swap out two collection views located in the same container

GalleryViewController_excerpt.swift

// MARK: - Animation

extension GalleryViewController {
    func animateCollectionViews(preview:Bool, with indexPath:IndexPath?) {
        guard let oldCollectionView = collectionView, let collectionViewModel = oldCollectionView.model else {
            return
        }

        let angle = CGFloat(Measurement(value: 90, unit: UnitAngle.degrees)
            .converted(to: .radians).value)
        closeButton.transform = preview ? CGAffineTransform.init(rotationAngle:angle) : .identity
        closeButton.isHidden = false
        
        var scrollToIndexPath = IndexPath(item: 0, section: 0)
        if let visibleIndexPath = indexPath {
            scrollToIndexPath = visibleIndexPath
        }
        
        let timingDuration:TimeInterval = 0.45 * (FeaturePolice.useSlowAnimation ? 4.0 : 1.0)
        
        let layout = collectionViewLayout(for: preview ? .horizontal : .vertical, errorHandler: oldCollectionView.model?.resourceDelegate?.errorHandler)
        let newCollectionView = galleryCollectionView(with: layout, collectionViewModel:collectionViewModel)
        
        newCollectionView.backgroundColor = preview ? .black : .white
        backingView.backgroundColor = newCollectionView.backgroundColor
        contentContainerView.backgroundColor = newCollectionView.backgroundColor
        headingContainerView.backgroundColor = view.backgroundColor
        topContentContainerCoverView.isHidden = preview
        bottomContentContainerCoverView.backgroundColor = preview ? UIColor.appDarkGrayBackground() : .white
        coverCollectionShadowView.backgroundColor = preview ? UIColor.appDarkGrayBackground() : UIColor.appLightGrayBackground()
        coverCollectionShadowView.layer.shadowOpacity = preview ? 0.0 : 0.1
        

        var appearance = GalleryCollectionViewImageCellAppearance()
        if preview {
            appearance.backgroundColor = .black
        } else {
            appearance.backgroundColor = .white
        }
        appearance.fadeDuration = timingDuration + 0.25
        
        newCollectionView.cellAppearance = appearance

        newCollectionView.alpha = 1.0

        contentContainerView.insertSubview(newCollectionView, at: 0)
        self.collectionView = newCollectionView
        
        setNeedsStatusBarAppearanceUpdate()
        refreshLayout(in: view)
        
        newCollectionView.scrollToItem(at: scrollToIndexPath, at: preview ? .centeredHorizontally : .centeredVertically, animated: false)
        newCollectionView.transform = CGAffineTransform.init(scaleX: 0.85, y: 0.95)
        
        let newCollectionAlphaAnimation = CABasicAnimation(keyPath: #keyPath(CALayer.opacity))
        newCollectionAlphaAnimation.fromValue = 0.0
        newCollectionAlphaAnimation.toValue = 1.0
        
        let oldCollectionAlphaAnimation = CABasicAnimation(keyPath: #keyPath(CALayer.opacity))
        oldCollectionAlphaAnimation.fromValue = 1.0
        oldCollectionAlphaAnimation.toValue = 0.0
        
        let headerColor = preview ? UIColor.appDarkGrayBackground() : UIColor.appLightGrayBackground()
        headingContainerView.backgroundColor = headerColor
        view.backgroundColor = headingContainerView.backgroundColor

        let timingFunction = CAMediaTimingFunction(controlPoints: 0.45, -0.4, 0.20, 1.25)
        CATransaction.begin()
        CATransaction.setAnimationDuration(timingDuration)
        CATransaction.setAnimationTimingFunction(timingFunction)
        CATransaction.setCompletionBlock {
            oldCollectionView.removeFromSuperview()
        }
        
        oldCollectionView.alpha = 0.0
        oldCollectionView.layer.add(oldCollectionAlphaAnimation, forKey: #keyPath(CALayer.opacity))
        
        newCollectionView.alpha = 1.0
        newCollectionView.layer.add(newCollectionAlphaAnimation, forKey: #keyPath(CALayer.opacity))
        
        UIView.animate(withDuration: timingDuration, animations: {
            newCollectionView.transform = .identity
        })
        
        let bottomConstant:CGFloat = preview ? -15 : -60
        previewContainerViewBottomConstraint.constant = bottomConstant
        
        if preview {
            for index in 1...4 {
                if let previewViewButtonImageView = previewContainerView.subviews.first?.subviews.first?.viewWithTag(index) {
                    
                    previewViewButtonImageView.alpha = 0.0
                    previewViewButtonImageView.transform = CGAffineTransform.init(scaleX: 0.25, y: 0.25)
                }
            }
        }
        
        view.setNeedsUpdateConstraints()
        UIView.animate(withDuration: timingDuration) { [weak self] in
            self?.view.layoutIfNeeded()
        }
        
        
        if preview {
            closeButton.alpha = 0.5
            
            UIView.animate(withDuration: timingDuration, animations: { [weak self] in
                self?.headingLabel.alpha = 0.0
                self?.headingLabel.transform = CGAffineTransform.init(scaleX: 0.5, y: 0.5)
                self?.closeButton.transform = .identity
                self?.closeButton.alpha = 1.0
            }) { (didSucceed) in
                if preview {
                    UIView.animate(withDuration: timingDuration / 2.0, animations: { [weak self] in
                        for index in 1...4 {
                            if let previewViewButtonImageView = self?.previewContainerView.subviews.first?.subviews.first?.viewWithTag(index) {
                                previewViewButtonImageView.alpha = 1.0
                                previewViewButtonImageView.transform = .identity
                            }
                        }
                    })
                }
            }
        } else {
            closeButton.alpha = 0.0
            closeButton.isHidden = true
            UIView.animate(withDuration: timingDuration, animations: { [weak self] in
                self?.headingLabel.alpha = 1.0
                self?.headingLabel.transform = .identity
                self?.closeButton.transform = CGAffineTransform.init(rotationAngle:angle)
            }) { (didSucceed) in
                
            }
        }
        
        CATransaction.commit()
    }
}