添加 UINavigationController 时崩溃 - swift

Question

Crash when adding a UINavigationController. I'm using this library and sample code:

https://github.com/appssemble/appstore-card-transition

let storyboard = UIStoryboard(name: "Main", bundle: nil)
let viewController = storyboard.instantiateViewController(withIdentifier: "type2") as! Type2ViewController

// Get tapped cell location
let cell = collectionView.cellForItem(at: indexPath) as! CardCollectionViewCell
cell.settings.cardContainerInsets = UIEdgeInsets(top: 8.0, left: 16.0, bottom: 8.0, right: 16.0)
cell.settings.isEnabledBottomClose = bottomDismiss

transition = CardTransition(cell: cell, settings: cell.settings)
viewController.settings = cell.settings
viewController.transitioningDelegate = transition
viewController.subtitle = "Bottom dismissible"
viewController.background = UIImage(named: "type2-bg-bottom")

viewController.modalPresentationStyle = .custom   
presentExpansion(viewController, cell: cell, animated: true)

Xcode Error logs:

Class AppstoreTransition.CardPresentationController overrides the -traitCollection getter, which is not supported. If you're trying to override traits, you must use the appropriate API.
Could not cast value of type 'UINavigationController' (0x1049b1338) to 'AppstoreTransition.CardsViewController' (0x1049b1308).
2019-06-29 15:39:24.077448+0200 TechSpec[10118:1200941] Could not cast value of type 'UINavigationController' (0x1049b1338) to 'AppstoreTransition.CardsViewController' (0x1049b1308).

Answer 1

First:

Force unwrapping values (using !) is in general bad practice and can (and should) be avoided most times. Force unwrapping guarantees to totally crash your app if somehow there is nothing to unwrap (nil).

Instead you should use something like if let or guard let, eg

guard let cell = collectionView.cellForItem(at: indexPath) as? CardCollectionViewCell else { debugPrint("uh-oh nil in here 🤓"; return }

or with an if let:

if let cell = collectionView.cellForItem(at: indexPath) as? CardCollectionViewCell {
    // your other code
} else {
    // handling the case when your cell is not of type CardCollectionViewCell
}

My guess for fixing your bug:

You did not set your custom class (inside your storyboard) to CardCollectionViewCell. See the example of a personal project below to find the right input field in Xcode. The example is for a TableView, but for your CollectionView it is the same.

• You have to select your custom cell
• Type in your custom class name
• Press Enter.

Otherwise, your cell will be a UICollectionViewCell by default.

In case you initialised your storyboard-cell via code, check if you really did initialize a cell of your custom type and not a UICollectionViewCell.