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).
Related
I have a table view in one view controller. I want to update the table view from another VC. I'm doing this using NotificationCenter like this:
In the table view VC:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(self.updateTableView), name: NSNotification.Name(rawValue: "updateTableView"), object: nil)
}
#objc func updateTableView() {
print("in func")
DispatchQueue.main.async {
self.listTV.reloadData()
}
}
In the opened VC:
func reloadTV() {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "updateTableView"), object: nil)
}
The print works, but the table view doesn't reload. I can only see it changing if I dismiss the VC with the table view and open it again.
I've followed the suggestions of other answers which is to use DispatchQueue, but that didn't make a difference. What am I missing?
Many thanks!
I would consider doing this by protocol and delegate instead of notifications...
This is how I do it.
When you call tableView.reloadData(). It has no effect if the tableView is hidden (isHidden == true). I believe the behavior is also the same when the tableView is effectively hidden by another ViewController (so effectively hidden).
Solution: A suggestion is to reload the tableView when the view is shown again. Few ways to do that.
one is in viewDidAppear (depends on how you transitioned between ViewControllers),
or
you can keep a reference to the tableView and after you dismiss the second ViewController (in which you were sending the notification) you provide the callback to reload the tableView. Roughly like the snippet, with self being the secondViewController you transitioned to. Dismiss that view
self.dismiss(animated: true, completion: {
self.tableView.reloadData()
}
or you can still use your notification and setup a flag and when the viewDidAppear, you then reloadData() inside viewDidAppear. However for this to work, you need to ensure that viewDidAppear is always called when the view is shown again (this will depend on how you transitioned between views).Simply override that method and print to verify.
There are other ways but the bottom line is tableView.reloadData() will be ignored if it is called when the tableView is not visible on the screen. My guess is it's an optimization made by Apple (no need to reload if no table is showing) or maybe a bug. I think they'll say it's a feature 😄
I suggest instead of using NotificationCenter, to instead set a Bool, tableViewNeedsUpdate, and check for the value of that Bool when the view with the UITableView is presented, and the UITableView is visible and able to accept reloadData() calls. After the reload is complete, set the variable back to false.
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)
The main ViewController is embedded in a UINavigationController subclass, and the VC has a subview that is loaded from a nib. The subview is called MenuView, and contains UIButtons that will link to other VCs.
To keep my main ViewController less unruly, I have put all these buttons into a subview that loads from a nib that animates the menu opening and closing.
However, I would like to present other view controllers from these, sometimes "Modally", sometimes "Show". What I have done seems to work, but I just want to know if this is alright, or if I have caused some unwanted effects that I'm unaware of (like a strong reference cycle that would cause a memory leak, or something). Or is there a better way to do this?
Some code:
In MenuView.swift
class MenuView: UIView {
var navigationController = CustomNavigationController()
func combinedInit(){
NSBundle.mainBundle().loadNibNamed("MenuViewXib", owner: self, options: nil)
addSubview(mainView)
mainView.frame = self.bounds
}
#IBAction func optionsAction(sender: AnyObject) {
self.navigationController.performSegueWithIdentifier("presentOptions", sender: self)
}
In ViewController.swift
menuView.navigationController = self.navigationController as! CustomNavigationController
Short answer: No, it is not alright to access a view controller from within some view in the hierarchy, because that would break all the MVC rules written.
UIView objects are meant to display UI components in the screen and are responsible for drawing and laying out their child views correctly. That's all there is. Nothing more, nothing less.
You should handle those kind of interactions between views and controllers always in the controller in which the view in question actually belong. If you need to send messages from a view to its view controller, you can make use of either the delegate approach or NSNotificationCenter class.
If I were in your shoes, I would use a delegate when view needs some information from its view controller. It is more understandable than using notification center as it makes it much easier to keep track of what's going on between. If the view controller needs some information from a view (in other words, the other way around), I'd go with the notification center.
protocol MenuViewDelegate: class {
func menuViewDidClick(menuView: MenuView)
}
class MenuView: UIView {
var weak delegate: MenuViewDelegate?
#IBAction func optionsAction(sender: AnyObject) {
delegate?.menuViewDidClick(self)
}
}
Let's look at what's going on at the view controller side:
class MenuViewController: UIViewController, MenuViewDelegate {
override func viewDidLoad() {
...
self.menuView.delegate = self
}
func menuViewDidClick(menuView: MenuView) {
navigationController?.performSegueWithIdentifier("presentOptions", sender: self)
}
}
For more information about communication patterns in iOS, you might want to take a look at this great article in order to comprehend how they work.
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.
In iOS app, there may be several view controllers. They may perform segues from one to another. the question is how to detect each view controller about whether it is dismissed or not when implementing segue. Thanks.
You have access to:
override func viewWillDisappear(animated: Bool) {
}
override func viewDidDisappear(animated: Bool) {
}
// Called when the view controller will be removed from memory.
deinit {
}
Which can help you managed things based on that state of a view controller.
I'm not sure if you can detect whether or not it was dismissed, but you can set a variable "viewControllerDismissed = true" in performSegueWithIdentifier that will be detected in the VC behind the one being dismissed.