So, I am using the Elastic Transition pod (Cocoapods), and when I transition my app crashes because the UITransitionContextFromViewControllerKey key is nil. I am really confused as to why that value would be nil. What are some probable causes and solutions to resolving this error?
So here is some of my code for when I am transitioning into the next view controller:
func handleTap(sender: AnyObject) {
transition.sticky = true
transition.transformType = .TranslateMid
transition.showShadow = true
transition.edge = .Left
transition.startingPoint = sender.center
performSegueWithIdentifier("mySegue", sender: self)
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
segue.destinationViewController.transitioningDelegate = transition
segue.destinationViewController.modalPresentationStyle = .Custom
}
Then, when it is trying to transition my app crashes complaining that this line of code (in Elastic Transition) is returning nil:
transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
According to the ElasticTransition Github page, if a view controller is presented modally with elastic transition, then the destination view controller's transitioningDelegate needs to be set to ElasticTransition and modalPresentationStyle to .Custom. However, if the view controller is pushed onto a navigation controller stack using the elastic transition, then only the navigationController?.delegate needs to be set to ElasticTransition.
After some chatting, #Harish told me that he uses a push segue. However, the code in prepareForSegue is the setup code for when one presents a view controller modally. That is likely the reason why UITransitionContextFromViewControllerKey returns nil. So I believe the solution is to set the navigationController's delegate to ElasticTransition somewhere, and remove the code in prepareForSegue.
Related
I am presenting a UISearchController programmatically, without adding it to the navigationItem. The Calendar app does something similar.
Without a presentation context, the search bar appears correctly, but persists after pushing another view controller.
This is expected, so we need to set definesPresentationContext on the list view controller... But that causes the search bar to render incorrectly.
Here's the code for context:
private lazy var searchController: UISearchController! = {
let searchController = UISearchController(searchResultsController: nil)
searchController.obscuresBackgroundDuringPresentation = false
// If this is set to true, the search bar animates correctly, but that's
// not the effect I'm after. See the next video.
searchController.hidesNavigationBarDuringPresentation = false
return searchController
}()
override func viewDidLoad() {
super.viewDidLoad()
definesPresentationContext = true
searchButton.rx.tap.subscribe(onNext: { [unowned self] in
present(searchController, animated: true)
}).disposed(by: disposeBag)
}
Setting hidesNavigationBarDuringPresentation kind of fixes it, but we lose the tab bar, and the whole thing just looks bad.
I tried this solution (Unable to present a UISearchController), but it didn't help.
Any suggestions?
UPDATE: The issue is, more specifically, that the search bar appears behind the translucent navigation bar. Making the nav bar solid ( navigationController?.navigationBar.isTranslucent = false) makes the search bar appear under the nav bar.
I have the same problem not been able to solve this either. It seems like the problem is that either
a) the searchcontroller is presented at the very top of the viewcontroller stack, even above the navigation controller, so that it stays active into the next viewcontroller push. or,
b) the searchcontroller is presented underneath the navigationcontroller so that it remains covered by the navigation bar
One idea: don't embed the viewcontroller which is presenting the searchcontroller in a navigation controller. instead, just create a UIView which looks like a navigation bar a the top. would this be an inappropriate solution?
I haven't found a solution to the original problem, but I found a workaround: intercept navigation events, and manually dismiss the search controller.
override func viewDidLoad() {
...
// This makes the search bar appear behind the nav bar
// definesPresentationContext = true
navigationController?.delegate = self
}
extension JobListViewController: UINavigationControllerDelegate {
func navigationController(_ navigationController: UINavigationController,
willShow viewController: UIViewController, animated: Bool) {
// `animated` is false because, for some reason, the dismissal animation doesn't start
// until the transition has completed, when we've already arrived at the new controller
searchController.dismiss(animated: false, completion: nil)
}
}
I found that presenting the search controller over the navigation bar can be achieved by calling present(_:animated:completion:) on the navigation controller itself rather than the navigation controller's child.
So in your view controller you can do
navigationController?.present(searchController, animated: true)
And this will behave like the search button in the Apple's Calendar app.
Update
Regarding dismissing the search controller before pushing a new controller to the navigation stack, you can do this manually depending on how the push is done.
All the bellow will animate dismissing the search controller before the push happens. Note that I disable user interaction until the dismiss animation completes to prevent pushing the same view controller multiple times.
UIStoryboardSegue
Add this override to your view controller:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if navigationController?.presentedViewController == searchController {
view.isUserInteractionEnabled = false
searchController.dismiss(animated: true) {
self.view.isUserInteractionEnabled = true
}
}
}
IBAction (Programmatically)
Just dismiss the search controller before pushing view controllers to the navigation stack:
#IBAction func showSecondTapped(_ sender: UIButton) {
// Dismiss the search controller first.
view.isUserInteractionEnabled = false
searchController.dismiss(animated: true) {
self.view.isUserInteractionEnabled = true
}
// Build and push the detail view controller.
if let secondViewController = storyboard?.instantiateViewController(withIdentifier: "SecondViewController") {
navigationController?.pushViewController(secondViewController, animated: true)
}
}
Handling pop gesture
If the view controller that is presenting the search controller is not the root of your navigation controller, the user might be able to use the interactive pop gesture, which will also keep the search controller presented after the pop. You can handle this by making your view controller the delegate for the search controller, conform to UISearchControllerDelegate and adding the following code:
extension ViewController: UISearchControllerDelegate {
func willPresentSearchController(_ searchController: UISearchController) {
navigationController?.interactivePopGestureRecognizer?.isEnabled = false
}
func willDismissSearchController(_ searchController: UISearchController) {
navigationController?.interactivePopGestureRecognizer?.isEnabled = true
}
}
I have a storyboard with two view controllers. First one, VC_1, has one button that opens 2nd one - VC_2.
VC_2 also has a button that opens VC_1.
Both controllers have almost identical code:
class VC_1: UIViewController
{
override func viewDidLoad()
{
super.viewDidLoad()
print(“VC_1 loaded")
}
override func viewDidAppear(_ animated: Bool){ print(“VC_1 appeared") }
override func viewDidDisappear(_ animated: Bool){ print(“VC_1 disappeared") }
#IBAction func btnShowVC_2(_ sender: UIButton)
{
let storyboard = UIStoryboard(name: "Main", bundle: nil)
secondVC = storyboard.instantiateViewController(identifier: “VC_2”)
secondVC.modalPresentationStyle = .fullScreen
show(secondVC, sender: self)
}
}
The difference is only in "VC_2" instead of "VC_1" in the 2nd controller code.
I have seen this View Controller creation code in Apple documentation and many other examples around the Internet.
When I press the button on the VC_1, I see in the debug window, that VC_2 is loaded and appeared, and VC_1 is disappeared. And same, of course, happens when I press the button on VC_2 - it disappears, and VC_1 is loaded again.
My questions are:
what happens with View Controller object after "viewDidDisappear" has been called? Does it really disappear from memory, or "disappear" only means "you cannot see it on the screen?". I do not see "viewDidUnload" in the documentation...
I suppose that "viewDidLoad" means that new View Controller object was created in memory. Is there any way to load the View Controller object only once, and then hide and show it without causing "viewDidLoad" to be called? I tried to do it with global variable "secondVC" but got "Application tried to present modally an active controller" error.
viewDidDisappear: called after the view is removed from the windows’
view hierarchy. No, View controller object just left the view property. By the way the amount of memory used by view controllers is negligible. So dont think about too much. If you want to catch when Your View controller object release from the memory put
deinit { print("vc deallocated") }
viewDidUnload, it has been deprecated since the iOS
6, which used to do some final cleaning.
Partly true. Keep in mind ViewDidload called one time for the life cycle of view controller. There is a method called before viewdidload but this is not related with your question.
In addition to "There is a method before viewdidload" -> loadView( ) is a method managed by the viewController. The viewController calls it when its current view is nil. loadView( ) basically takes a view (that you create) and sets it to the viewController’s view (superview).
It's easier to show you a drawing and then explain.
Dashboard Storyboard
I have 2 separate UIViewControllers (i've included just one in the drawing, the other is irrelevant) embedded in container view called ContainerViewController.
Post Storyboard
NewPostViewController shows a UIButton that presents TextPostViewController. As you can see, all of them are embedded in UINavigationControllers. Now, once the completion block of the new post is being called, I have to present the ContainerViewController and it needs to handle it's own logic. The problem is that it's embedded in UINavigationController and once I present it, the UITaBbar is hidden.
I tried to do this:
self.performSegue(withIdentifier: "TextPostToNavContainerVC", sender: nil)
The transition is successful but I'm losing the UITabBar, even though in the DashboardViewController and the ContainerViewController I called:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
tabBarController?.tabBar.isHidden = false
}
What am I doing wrong or is there are better way to do that?
You should instantiate the tab bar controller. not the view controller.
Imagine you're putting a initial view controller ahead of your tab bar controller. Making your tab bar not being pushed
If I undestand it correctly.
You are doing this
Segue connect to a view controller
But you should actually do this Segue connected to a tab bar controller
You can try to add it as a child to control it's frame like this
let textPost = self.storyboard?.instantiateViewController(withIdentifier: "containerID") as! TextPostToNavContainerVC
textPost.view.frame = CGRect(x:20,y:0,width:self.view.frame.width,height:self.view.frame.height-50)
self.view.addSubview(nvc.view)
self.addChildViewController(textPost)
textPost.didMove(toParentViewController: self)
I have a working simple single player game, where the initial view controller has a button to start the game. This button performs a segue and all game logic in the GameViewController is working as expected.
I've followed this tutorial to add multi player functionality to my game.
On the initial view controller, a button now calls
GameKitHelper.sharedGameKitHelper.findMatchWithMinPlayers(2, maxPlayers: 2, viewController: self, delegate: MultiPlayerNetworking)
}
which has the following implementation in GameKitHelper.swift:
func findMatchWithMinPlayers (minPlayers: Int, maxPlayers: Int, viewController: UIViewController, delegate: GameKitHelperDelegate) {
matchStarted = false
let request = GKMatchRequest()
self.delegate = delegate
request.minPlayers = 2
request.maxPlayers = 2
presentingViewController = viewController
presentingViewController.dismissViewControllerAnimated(false, completion: nil)
let mmvc = GKMatchmakerViewController(matchRequest: request)
mmvc?.matchmakerDelegate = self
presentingViewController.presentViewController(mmvc!, animated: true, completion: nil)
self.delegate?.matchStarted()
}
The Class MultiPlayerNetworking implements the GameKitHelper protocol, and gets called on the matchStarted function.
The MultiPlayerNetworking class in essence takes over here, and starts sending out messages to hosts and remote players.
Note that some time later, When auto-matching finishes, the following function gets called in GameKitHelper:
func matchmakerViewController(viewController: GKMatchmakerViewController, didFindMatch match: GKMatch) {
viewcontroller.dismissViewControllerAnimated(true, completion: {})
self.match = match
match.delegate = self
}
Now, I think this says that the GKMatchmakerViewController is dismissed, thereby showing me the initial view controller again (and this is what happens on screen).
Now my issue! After the GKMatchmakerViewController is dismissed, I'm back at the initial view controller and want to 'simulate' an automatic segue to my gameView (which has logic to deal with a multi player game as well).
I've made the initial view controller conform to the MultiPlayerNetworking protocol, which has a function to simulate a segue:
func segueToGVC() {
self.performSegueWithIdentifier("game", sender: nil) // self = initial view controller
}
However, xCode complains with:
Warning: Attempt to present <GameViewController: 0x7d440050> on <GKMatchmakerViewController: 0x7c8fbc00> whose view is not in the window hierarchy!
I'm stuck here, and have tried so many different methods of dismissing the view controller, to making sure I'm calling the performSegue function on the topViewController via this link, but nothing works.
My question: why is the GKMatchmakerViewController visually dismissed, but still present in the view hierarchy, such that calling a performSegue function on the initial view controller give the above error/warning?
Views are greatly appreciated!
why is the GKMatchmakerViewController visually dismissed, but still present in the view hierarchy
Here are two suggestions:
Perhaps it's because dismissal takes time. You are saying:
viewcontroller.dismissViewControllerAnimated(true, completion: {})
So there's an animation. Don't attempt to perform the next segue until the animation is over.
Perhaps you are just wrong about who self is. You are saying:
self.performSegueWithIdentifier("game", sender: nil)
// self = initial view controller
We have only your word, in that comment, for who self is. Meanwhile, the runtime seems to think differently about the matter:
Attempt to present <GameViewController: 0x7d440050> on <GKMatchmakerViewController: 0x7c8fbc00>
It might be good to believe the runtime; after all, it knows more than you do.
i'm fairly new to swift and having some difficulty with unwind segues in a master detail application.
the unwind seems to work fine dismissing my popovers on the iPhone, however when i try the same thing on the iPad, the popover remains.
If i add a dismissViewControllerAnimated to the presenting viewController's unwind handling action, then the iPad version works fine and dismisses the popover, however the iPhone version dismisses the popover and then dismisses the view that presented the popover. i.e. dismisses two views.
I have worked out that the problem is that popover's are automatically dismissed with an unwind when presented modally such as on an iPhone. However when presented as true popovers they don't dismiss with an unwind segue. Could somebody help me figure out how to manage both cases so that only the popover will be dismissed. Thank you very much in advance.
Okay. after a long time working on this i managed to come up with a solution. i used a popoverpresentationcontroller and declared the presenting controller as the delegate. by then adding an additional function forcing the iPhone to use the popover in lieu of the modal presentation, the presentation and dismissal is consistent for the iPhone and iPad. the code is below. I just used a generic UIViewController in the if let vc statement so that I could use this with a popover that's imbedded in a navigation controller also.
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let identifier = segue.identifier {
switch identifier {
case "My Segue Identifier" :
if let vc = segue.destinationViewController as? UIViewController {
if let ppc = vc.popoverPresentationController {
ppc.delegate = self
}
}
default: break
}
}
}
additionally you need to add the following function to prevent the modal presentation on the iPhone:
func adaptivePresentationStyleForPresentationController (controller:UIPresentationController)-> UIModalPresentationStyle {
return UIModalPresentationStyle.None
}