ZoomTransitionAnimator

ZoomTransitionAnimator is a transition animator between view controllers. It zooms the whole scene together, not just the cell or image view you selected. Multi-layer zooming (zoom-in from view controller A to B and then to C) is supported. Although not an interactive transition animator, you can use it with UIPanGestureRecognizer. As long as you return the correct frame of the target view in absolute space (UIScreen.main.coordinateSpace), the animator will find it and zoom out from there.

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Installation

ZoomTransitionAnimator is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'ZoomTransitionAnimator'

Usage

1. Initialize and return a ZoomTransitionAnimator object in your UINavigationControllerDelegate object.

    extension NavigationViewController: UINavigationControllerDelegate {
        func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
            switch (fromVC, toVC) {
            case (let zoomSourceVC as ZoomTransitionSource, let zoomDestinationVC as ZoomTransitionDestination):
                guard let operation = ZoomTransitionOperation(rawValue: operation.rawValue) else { return nil }
                return ZoomTransitionAnimator(duration: 0.45, damping: 0.75, source: zoomSourceVC, destination: zoomDestinationVC, operation: operation)
            default:
                return nil
            }
        }
    }
   

2. Apply both ZoomTransitionSource and ZoomTransitionDestination protocols to your ParentViewController. Or if you only want the zoom animation to appear in only one direction, choose one of them to apply.

    extension ParentViewController: ZoomTransitionSource {
        func zoomTransitionAnimator(_ animator: ZoomTransitionAnimator, targetViewBeginningFrameFor operation: ZoomTransitionOperation) -> CGRect {
            switch operation {
            case .zoomIn:
                return selectedCellImageViewFrame
            case .zoomOut:
                fatalError()
            }
        }
    }
   
    extension ParentViewController: ZoomTransitionDestination {
        func zoomTransitionAnimator(_ animator: ZoomTransitionAnimator, targetViewFinalFrameFor operation: ZoomTransitionOperation) -> CGRect
            switch operation {
            case .zoomIn:
                fatalError()
            case .zoomOut:
                return selectedCellImageViewFrame
            }
        }
    }
   

Since the ParentViewController is not going to be a zoom-in destination, you could put fatalError() there. These cases were designed for when a ViewController is both zoom-out destination and zoom-in destination. That is, multi-layer zooming.

3. Apply those protocols to your ChildViewController too.

    extension ChildViewController: ZoomTransitionSource {
        func zoomTransitionAnimator(_ animator: ZoomTransitionAnimator, targetViewBeginningFrameFor operation: ZoomTransitionOperation) -> CGRect {
            switch operation {
            case .zoomIn:
                fatalError()
            case .zoomOut:
                return imageViewFrame
            }
        }
    }
   
    extension ChildViewController: ZoomTransitionDestination {
        func zoomTransitionAnimator(_ animator: ZoomTransitionAnimator, targetViewFinalFrameFor operation: ZoomTransitionOperation) -> CGRect
            switch operation {
            case .zoomIn:
                return imageViewFrame
            case .zoomOut:
                fatalError()
            }
        }
    }
   

And that's it, really. You don't have to return any UIView, just the frame of it. So if you want to zoom out from the content of a UIScrollView, just calculate the frame with scrollView.contentOffset and scrollView.contentSize. No need to make a snapshot view anymore.

Author

yesleon, yesleon@me.com

License

ZoomTransitionAnimator is available under the MIT license. See the LICENSE file for more info.