I can't find a clear definition of what UIScenes are
Are they just for handling the background calls? Are they like a ViewController? Do we use them often or nah?
The biggest thing is that scenes set up multiple window support. It is also useful for SwiftUI.
The SceneDelegate controls what is displayed on the screen "to manage life-cycle events in one instance of your app's user interface.", while the AppDelegate controls your entire app life-cycle.
Read the App and Environment Article and scenes from Apple instead of UIScene documentation.
Scene:
Scene, Manage multiple instances of your app’s UI simultaneously, and
direct resources to the appropriate instance of your UI.
We had only one scene back then before iOS 13, So the only thing we need to run ViewControllers simultaneously was multiple Windows on top of each other. But now, each application can have multiple instances running at the same time! Each scene has its own state and it might be in the foreground while others are in the background or are suspended, while Window was completely dependent on the application itself.
Imagine we have 2 view controllers (consider there are no scenes) running on the left and right side of the device and then we need to show a banner. Using the old window method will show the banner on both of them! And if you need to pick one, you may end up finding the correct controller and presenting the banner on it.
So apple introduced Scene, a container for each separate instance of the app. So you can manage each one separately and each of them acts as a separate app. It has its own windows and controllers. But all of them are managed by a single object, UIApplication.shared and it has a delegate to handle general events (usually from outside of the app) and entire application life cycle.
Related
Should my app be updated to Scene Delegate from App Delegate. My app supports ios 13.0 and up
first you have to understand what is difference
You could think of them as the global and private versions. One is shared and the other is limited to the individual owner. In a way, they are exactly what you would expect by the names.
Multi-window support is happening
Next time you create a new Xcode project you’ll see your AppDelegate has split in two: AppDelegate.swift and SceneDelegate.swift. This is a result of the new multi-window support that landed with iPadOS, and effectively splits the work of the app delegate in two.
From iOS 13 onwards, your app delegate should:
Set up any data that you need for the duration of the app.
Respond to any events that focus on the app, such as a file being shared with you.
Register for external services, such as push notifications.
Configure your initial scenes.
In contrast, scene delegates are there to handle one instance of your app’s user interface. So, if the user has created two windows showing your app, you have two scenes, both backed by the same app delegate.
Keep in mind that these scenes are designed to work independently from each other. So, your application no longer moves to the background, but instead individual scenes do – the user might move one to the background while keeping another open.
at last I will say that you can go with Scene Delegate
Courtesy of https://www.hackingwithswift.com/articles/193/whats-new-in-ios-13
I am developing an iOS application that allows someone to play one of two different games.
Both games are played in a set of rounds. When a player finishes a round the application transitions to a new scene that displays results and then either transitions to another round scene or an end game scene.
Because of the transient nature of the scenes in the application, it makes little sense to persist scenes as is done in more traditional applications, where someone can return to a previous scene.
To that end, most scene navigation is accomplished by using a UINavigationViewController and simply calling setViewControllers(animated:) supplying an array that contains only the UIViewController for the next scene, and this works quite well.
I mentioned that the application will allow someone to play one of two games. It turns out that, on the iPhone, one game is best played in portrait mode, and the other game works best played in landscape mode. I want to be able to control what user interface orientation is used for a particular UIViewController when it becomes active.
I have experimented with using the supportedInterfaceOrientations property of the UINavigationController and application(_ application: supportedInterfaceOrientationsFor window:) for UIApplicationDelegate, and have been able to get things to work for a standard application. However, when I try to apply things to the way my game application works using setViewControllers(animated:), no methods that pertain to applying the desired user interface orientation seem to get called, and all scenes appear at the same orientation.
What suggestions do people have for how I could get a scene in my application to appear with a particular user interface orientation?
Try making your presented view controller call the following method on it's view will appear, or view did appear:
class func attemptRotationToDeviceOrientation()
Some view controllers may want to use app-specific conditions to
determine what interface orientations are supported. If your view
controller does this, when those conditions change, your app should
call this class method. The system immediately attempts to rotate to
the new orientation.
https://developer.apple.com/documentation/uikit/uiviewcontroller/1621400-attemptrotationtodeviceorientati
I have a doubt:
I have an app with 10 views. I want that, if the user is on View1 and sends the app to the background, it terminates the application (exit (0)). But I wanted this to happen only on View1, on the other screens, if the app goes to the background and then returns, it will continue where it left off.
What can I do?
Apple's guidelines seem to be strictly against terminating your app programmatically (for example, with exit()); it would go against what iOS users expect of how apps work.
Instead, I recommend the following approach:
When the app is sent to the background (applicationWillResignActive(_:) is called), check which view controller is currently being displayed.
If it's such that you wish to start over next time the app is brought to the foreground, just reset the app window's root view controller to whatever the initial view controller of your app is (typically, it involves reloading the inital view controller from Main.stroyboard, but your setup could be different).
You can not choose at runtime whether your app goes to the background or is terminated when the user presses the home button ("multitasking"); that is set in stone in your Info.plist file at build time.
Also, remember that even if you are in the screen that you wish to preserve when the user resumes, your app might be terminated by the system while it is in the background (to reclaim scarce system resources), so in that case it will still start from the initial screen. To prevent this, you might want to check out the APIs for state preservation and restoration.
Here is another SO question asking how to find the identity of the current view controller. Why not query the current view when you receive applicationWillResignActive indicating that your app is going to move to the background and then choose the action you want?
As far as I understand your description Preserving and Restoring State is what you are looking for.
Excerpt from Documentation:
The preservation and restoration process is mostly automatic, but you need to tell iOS which parts of your app to preserve. The steps for preserving your app’s view controllers are as follows:
Required
Assign restoration identifiers to the view controllers whose
configuration you want to preserve; see Tagging View Controllers for
Preservation.
Tell iOS how to create or locate new view controller objects at
launch time; see Restoring View Controllers at Launch Time.
Optional
For each view controller, store any specific configuration data needed to return that view controller to its original configuration; see Encoding and Decoding Your View Controller’s State.
Here is a link to Preserving Your App’s Visual Appearance Across Launches
I have an ARKit app which allows the user to add a cube to the scene. This works fine and I can see the cube. But when I push the app to the background and then move the device to another location (by walking to a different room) then ARKit session is unable to determine the correct position of my old nodes.
Is there anyway I can find a workaround this problem so that when the app is resumed from coming to foreground from the background then it still remembers the position of the nodes.
UPDATE: I am looking into saving the lat and long for the user and then somehow converting those lat and long to SCNVector3 to put the node.
You probably won't be able to keep the AR running in the background. Apple does not recommend pausing the session or interrupting it and trying to resume:
Avoid interrupting the AR experience. If the user transitions to another fullscreen UI in your app, the AR view might not be an expected state when coming back.
Use the popover presentation (even on iPhone) for auxiliary view controllers to keep the user in the AR experience while adjusting settings or making a modal selection. In this example, the SettingsViewController and VirtualObjectSelectionViewController classes use popover presentation.
The issue is that once the session gets interrupted, the device stops using it's mechanisms that keep track of AR Nodes as well as your location, might have to set up a mechanism that keeps the app running constantly in the background and running the ARSession through that. You might be able to find projects on github that allow for running in the background. Another issue you might face is Apple's limitations with running apps in the background, which is apparently 3 minutes.
If you're at all interested in restarting the AR Session one you came back in, you can see my answer on this thread.
I'm developing a small app on top of core data. At startup, I need to launch a maintenance task - fast but important -. To run this task, the app delegate must open a UIManagedDocument, and perform various checks on it. The app views must not start until the checks are completed. Because opening a UIMD is asynchronous, the app delegate isn't done when the first UIview tries to access the doc. The application then crashes due to a race condition because the app delegate and the view are trying to open the doc at the same time, while the doc state isn't yet finalised.
I'm using a storyboard, so segues are pretty much in control of the OS... Next time, I'll do it all manually..
What would be your recommendations ?
Note:
1)I can not perform the task when the app. goes into background state, because if it is brought back up again, avoiding inconsistent states between the underlying database and what's displayed in the view will be very tedious.
2)For the same reasons, performing the maintenance task during normal execution is not easily done.
3) All views access the UIMD via a singleton, according to the code proposed here
Setting a mutex lock in the UIView isn't my preferred route, because the screen remains black - no data -, while displaying the tab bars, until it is released by the app delegate.
Is there a way to have the app delegate wait for a signal before it hands the control over to the UIViews ? In this case, are there any gotchas ? I suspect this is probably not the recommended way to do, and iOS might kill the app if the delegate stays too long waiting for the maintenance task to complete. What would be "too long" in this case?
You could do it more elegant way. The first view the user will see must be some kind of SplashView - just an image with progress indicator. It should stay on top while your task is going on. It's not too important how you're showing this view. You can set it as the first in your storyboard or just create it manually in applicationDidFinishLaunching message.
Then in your task send a NSNotification when it's about to finish and in the observer in your AppDelegate just hide your SplashView and present your first view with valuable content.
You can even add some visual effects for transition between those views and your app will look really great! :)