I have a label that displays the state of the app. as far as I can tell, there is no way to call UIApplicationDelegate protocol methods inside the ViewController and Views can't be linked to AppDelegate. It's like the app is split into two parts that can't communicate with each other.
You can always using notifications...
Apple Docs
Tutorial for listening to application moved to background:
override func viewDidLoad() {
super.viewDidLoad()
let notificationCenter = NotificationCenter.default
notificationCenter.addObserver(self, selector: #selector(appMovedToBackground),
name: Notification.Name.UIApplicationWillResignActive, object: nil)
}
#objc func appMovedToBackground() {
print("App moved to background!")
}
Related
I created an outlet in ViewController class and I'd like to modify it.
In the ViewController.swift file I have
import Cocoa
class ViewController: NSViewController {
#IBOutlet var LabelText: NSTextFieldCell?
override func viewDidLoad() {
super.viewDidLoad()
}
//other things
}
I'd like to change the background color of the label. How can I do that from AppDelegate?
At first I thought I could solve this problem using a function in ViewController and calling it in AppDelegate
func changeBackground() {
LabelText.textColor = NSColor.red
}
But soon I realised that it wasn't possible unless I used a static function. Then I tried to modify the code in ViewController like that
static func changeBackground() {
LabelText.textColor = NSColor.red
}
and call this function in AppDelegate like that
ViewController.changeBackground()
In this way I can access to changeBackground() function from AppDelegate, but in ViewController it gives me an error: Instance member 'LabelText' cannot be used on type 'ViewController'
I understood that this cannot be possible because somehow I'm calling "LabelText" before it's initialised (or something like that).
I don't know much about Swift and I'm trying to understand how it works. I've been searching for the answer to my question for hours, but still I don't know how to solve this.
Solution
As Rob suggested, the solution is to use NotificationCenter.
A useful link to understand how it works: https://www.appypie.com/notification-center-how-to-swift
Anyway, here how I modified the code.
In ViewController:
class ViewController: NSViewController {
#IBOutlet var label: NSTextFieldCell!
let didReceiveData = Notification.Name("didReceiveData")
override func viewDidLoad() {
NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveData(_:)), name: didReceiveData, object: nil)
super.viewDidLoad()
}
#objc func onDidReceiveData(_ notification: Notification) {
label.textColor = NSColor.red
}
}
And then, in AppDelegate:
let didReceiveData = Notification.Name("didReceiveData")
NotificationCenter.default.post(name: didReceiveData, object: nil)
I'm working on digital banking app. I need the user to be re prompted for PIN/Password after the app enter background for more than X seconds. I look up scene delegate's functions but I have no idea how can I check how long the user has been in foreground and how to popping out the view. I use AppDelegate and SceneDelegate for lifecycle
you can do this by using local notification what you have to do is following.
easy steps for new user
manage a global object for app state // if needed
add a local notification in your main view controller
post a notification from your SceneDelegate
here is the example
add observer in your main controller which always appears when app start or launch
class MainViewController: UIViewController
{
override func viewDidLoad()
{
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(showPopup(notification:)), name:
NSNotification.Name(rawValue: "showPinCodePopup"), object: nil)
}
// remove observer
override func viewWillDisappear(_ animated: Bool)
{
NotificationCenter.default.removeObserver(self)
}
#objc func showPopup(notification: NSNotification) {
//show your popup here
}
}
call the local notification from your SceneDelegate when app becomes active or enter in Foreground.
class SceneDelegate: UIResponder, UIWindowSceneDelegate
{
var window: UIWindow?
func sceneDidBecomeActive(_ scene: UIScene) {
NotificationCenter.default.post(name: Notification.Name(rawValue:"showPinCodePopup"), object: nil, userInfo:nil)
// Called when the scene has moved from an inactive state to an active state.
// Use this method to restart any tasks that were paused (or not yet started) when the scene was inactive.
}
}
Hope this solution may helps you 😊
I am building an iOS app using the new language Swift. Now it is an HTML5 app, that displays HTML content using the UIWebView. The app has local notifications, and what i want to do is trigger a specific javascript method in the UIWebView when the app enters foreground by clicking (touching) the local notification.
I have had a look at this question, but it does not seem to solve my problem. I have also come across this question which tells me about using UIApplicationState, which is good as that would help me know the the app enters foreground from a notification. But when the app resumes and how do i invoke a method in the viewController of the view that gets displayed when the app resumes?
What i would like to do is get an instance of my ViewController and set a property in it to true. Something as follows
class FirstViewController: UIViewController,UIWebViewDelegate {
var execute:Bool = false;
#IBOutlet var tasksView: UIWebView!
}
And in my AppDelegate i have the method
func applicationWillEnterForeground(application: UIApplication!) {
let viewController = self.window!.rootViewController;
let mainStoryboard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
var setViewController = mainStoryboard.instantiateViewControllerWithIdentifier("FirstView") as FirstViewController
setViewController.execute = true;
}
so what i would like to do is when the app enters foreground again, i want to look at the execute variable and run the method as follows,
if execute{
tasksView.stringByEvaluatingJavaScriptFromString("document.getElementById('sample').click()");
}
Where should i put the code for the logic to trigger the javascript from the webview? would it be on viewDidLoad method, or one of the webView delegate methods? i have tried to put that code in the viewDidLoad method but the value of the boolean execute is set to its initial value and not the value set in the delegate when the app enters foreground.
If I want a view controller to be notified when the app is brought back to the foreground, I might just register for the UIApplication.willEnterForegroundNotification notification (bypassing the app delegate method entirely):
class ViewController: UIViewController {
private var observer: NSObjectProtocol?
override func viewDidLoad() {
super.viewDidLoad()
observer = NotificationCenter.default.addObserver(forName: UIApplication.willEnterForegroundNotification, object: nil, queue: .main) { [unowned self] notification in
// do whatever you want when the app is brought back to the foreground
}
}
deinit {
if let observer = observer {
NotificationCenter.default.removeObserver(observer)
}
}
}
Note, in the completion closure, I include [unowned self] to avoid strong reference cycle that prevents the view controller from being deallocated if you happen to reference self inside the block (which you presumably will need to do if you're going to be updating a class variable or do practically anything interesting).
Also note that I remove the observer even though a casual reading of the removeObserver documentation might lead one to conclude is unnecessary:
If your app targets iOS 9.0 and later or macOS 10.11 and later, you don't need to unregister an observer in its dealloc method.
But, when using this block-based rendition, you really do need to remove the notification center observer. As the documentation for addObserver(forName:object:queue:using:) says:
To unregister observations, you pass the object returned by this method to removeObserver(_:). You must invoke removeObserver(_:) or removeObserver(_:name:object:) before any object specified by addObserver(forName:object:queue:using:) is deallocated.
I like to use the Publisher initializer of NotificationCenter. Using that you can subscribe to any NSNotification using Combine.
import UIKit
import Combine
class MyFunkyViewController: UIViewController {
/// The cancel bag containing all the subscriptions.
private var cancelBag: Set<AnyCancellable> = []
override func viewDidLoad() {
super.viewDidLoad()
addSubscribers()
}
/// Adds all the subscribers.
private func addSubscribers() {
NotificationCenter
.Publisher(center: .default,
name: UIApplication.willEnterForegroundNotification)
.sink { [weak self] _ in
self?.doSomething()
}
.store(in: &cancelBag)
}
/// Called when entering foreground.
private func doSomething() {
print("Hello foreground!")
}
}
Add Below Code in ViewController
override func viewDidLoad() {
super.viewDidLoad()
let notificationCenter = NotificationCenter.default
notificationCenter.addObserver(self, selector:#selector(appMovedToForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
#objc func appMovedToForeground() {
print("App moved to foreground!")
}
In Swift 3, it replaces and generates the following.
override func viewDidLoad() {
super.viewDidLoad()
foregroundNotification = NotificationCenter.default.addObserver(forName:
NSNotification.Name.UIApplicationWillEnterForeground, object: nil, queue: OperationQueue.main) {
[unowned self] notification in
// do whatever you want when the app is brought back to the foreground
}
In my app, there is a ViewController.swift file and a popupViewController.swift file. Inside the app, when I open the popupViewController with storyboard segue as presentModally and then come back from popupViewController to ViewController with the code dismiss(), the methods viewDidLoad, viewWillAppear, viewDidAppear, ViewWillLayoutSubviews etc. nothing works, they execute just once and don't repeat when I go and return back. So, I want to execute the code every time when viewController.swift is active. I couldn't find a useful info in stackoverflow about this.
Meanwhile, I don't know much about notification and observers(if certainly needed), therefore, can you tell step by step in detail how to do that in Swift (not objective-c)? I mean how to determine if current view controller is active.
Edit: I am navigating from StoryBoard segue, presentModally. There is no Navigation Controller in storyboard.
I tried some codes but nothing happens. The point I came so far is:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector:#selector(appWillEnterForeground), name:UIApplication.willEnterForegroundNotification, object: nil)
}
#objc func appWillEnterForeground() {
print("asdad") //nothing happens
if self.viewIfLoaded?.window != nil {
// viewController is visible
print("CURRENT VÄ°EW CONTROLLER") //nothing happens
}
}
As mention in my comments, I don't use storyboards. There may be a way to create an unwind segue - or maybe not - but [here's a link][1] that may help you with a storyboard-only way of fixing your issue. A quick search on "modal" turned up 9 hits, and the second one starts going into details.
I'm thinking the issue is with what modality is. Basically, your first view controller, which properly executed viewDidAppear, is still visible. So it's effectively not executing viewDidDisappear when your second VC is presented.
You might want to change your concept a bit - an application window (think AppDelegate and/or SceneDelegate become active, where a UIViewController has a is initialized and deinitialized, along with a root UIView that is loaded, appears* and disappears*. This is important, because what you want to do is send your notification from the modal VC's viewDidDisappear override.
First, I find it easiest to put all your notication definitions in an extension:
extension Notification.Name {
static let modalHasDisappeared = Notification.Name("ModalHasDisappeared")
}
This helps not only reduce string typos but also is allows Xcode's code completion to kick in.
Next, in your first view controller, ad an observer to this notification:
init() {
super.init(nibName: nil, bundle: nil)
NotificationCenter.default.addObserver(self, selector: #selector(modalHasDisappeared), name: .modalHasDisappeared, object: nil)
}
required init?(coder: NSCoder) {
super.init(coder: coder)
NotificationCenter.default.addObserver(self, selector: #selector(modalHasDisappeared), name: .modalHasDisappeared, object: nil)
}
#objc func modalHasDisappeared() {
print("modal has disappeared")
}
I've added both forms of init for clarity. Since you are using a storyboard, I'd expect that init(coder:) is the one you need.
Finally, just send the notification when the modal has disappeared:
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
NotificationCenter.default.post(name: .modalHasDisappeared, object: nil, userInfo: nil)
}
This sends no data, just the fact that the modal has disappeared. If you want to send data - say, a string or a table cell value, change the object parameter to it:
NotificationCenter.default.post(name: .modalHasDisappeared, object: myLabel, userInfo: nil)
And make the following changes in your first VC:
NotificationCenter.default.addObserver(self, selector: #selector(modalHasDisappeared(_:)), name: .modalHasDisappeared, object: nil)
#objc func modalHasDisappeared(_ notification:Notification) {
let label = notification.object as! UILabel!
print(label.text)
}
Last notes:
To repeat, note that by declaring an extension to Notification.Name, I've only have one place where I'm declaring a string.
There is no code in AppDelegate or SceneDelegate, nor any references to `UIApplication(). Try to think of the view (and view controller) as appearing/disappearing, not background/foreground.
While the first view is visually in the background, it's still visible. So the trick is to code against the modal view disappearing instead.
I want to reload data in UIViewController when application become active or become foreground.
I know applicationDidBecomeActive is called in AppDelegate class.
But I have to have a global variable for the UIViewController to reload its data in AppDelegate class like this code:
in AppDelegate.m
// global variable
UIViewController *viewController1;
UIViewController *viewController2;
-(void)applicationDidBecomeActive:(UIApplication *)application
{
[viewController1 reloadData];
[viewController2 reloadData];
}
But it is inconvenient especially when I have a lot of UIViewControllers.
Can I use applicationDidBecomeActive in UIViewController instead of in AppDelegate class?
Or are there better ways than having global variable for UIViewController?
I also need to use the following method from UIViewControllers:
-(void)applicationWillResignActive:(UIApplication *)application
-(void)applicationDidEnterBackground:(UIApplication *)application
-(void)applicationWillEnterForeground:(UIApplication *)application
At the time of reactivation, if you want to carry a particular thing for a view controller, you should register a notification in its viewDidLoad method.
UIApplicationDidBecomeActiveNotification will automatically notify your application and given controller, if they registered for it.
[[NSNotificationCenter defaultCenter]addObserver:self
selector:#selector(yourMethod)
name:UIApplicationDidBecomeActiveNotification
object:nil];
Here is an example of registering a notification handler in Swift (adapted from Apurv's answer above):
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(
self,
selector: #selector(applicationDidBecomeActive(notification:)),
name: NSNotification.Name.UIApplicationDidBecomeActive,
object: nil)
}
#objc func applicationDidBecomeActive(notification: NSNotification) {
// do something
}
Update for Swift 4.2:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
}
#objc func applicationDidBecomeActive(notification: NSNotification) {
// Application is back in the foreground
print("active")
}
Swift 3:
NotificationCenter.default.addObserver(
self,
selector: #selector(applicationDidBecomeActive(_:)),
name: NSNotification.Name.UIApplicationDidBecomeActive,
object: nil)
func applicationDidBecomeActive(_ notification: NSNotification) {
// do something
}
Note: Don't forget to remove the observer
You cannot use applicationDidBecomeActive in viewController; it is not a method for that class.
However, you can use applicationDidBecomeActive method in AppDelegate to call any methods in your view controller that you feel are important upon launch. Just keep a pointer to your controller so the App Delegate can reach it.
What those methods might be in your view controller is entirely up to you and the details of your program. Maybe it means calling a custom update method in your view controller or whatever else you feel is necessary.
You could also use NSNotificationCenter as outlined here, with many system notifications available for application launch: http://developer.apple.com/library/ios/#DOCUMENTATION/UIKit/Reference/UIApplication_Class/Reference/Reference.html
However, relying heavily on NSNotificationCenter is in my opinion a good way for an app to be come disorganized. If you call everything from your main methods in the AppDelegate only, you can always refer to that method to know exactly what your app is doing upon launch. If instead you use NSNotificationCenter, you could have actions spread across many classes/objects and it can be harder to track down what is going on. Since you mentioned multiple controller objects, I think it is more streamlined and organized to call everything from applicationDidBecomeActive rather than register each viewcontroller for the same notification.
update for swift 5
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
}
// remove the observer
deinit {
print("Receiver teardown")
NotificationCenter.default.removeObserver(self)
}
#objc func applicationDidBecomeActive(notification: NSNotification) {
// Application is back in the foreground
print("applicationDidBecomeActive")
}
}
just Use NotificationCenter in your UIViewController :
NotificationCenter.default.addObserver(self,
selector: #selector(applicationWillResignActive),
name: UIApplication.willResignActiveNotification,
object: nil)
Thank you all for answering my question.
But I found easier way to use applicationDidBecomeActive in UIViewController.
#implementation AppDelegate
-(void)applicationDidBecomeActive:(UIApplication *)application
{
UIViewController<MyAppDelegate> *topViewController = (UIViewController<MyAppDelegate> *)navigationController.topViewController;
if ([topViewController respondsToSelector:#selector(MyApplicationDidBecomeActive)]) {
[topViewController MyApplicationDidBecomeActive];
}
}
#end
#protocol MyAppDelegate
#optional
-(void)MyApplicationDidBecomeActive;
#end