I have a UIView similar to the one you can see below:
class ViewTaskViewController: UIViewController, UITableViewDataSource, UITableViewDelegate {
override func viewDidLoad() {
super.viewDidLoad()
subscribeToNotifications()
}
func subscribeToNotifications() {
let notification = NotificationCenter.default
notification.addObserver(forName: Notification.Name(rawValue: "TimerUpdated"), object: nil, queue: nil, using: handleUpdateTimer)
print("Subscribed to NotificationCenter in ViewTaskViewController")
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
print("TUFU TUFU TUFU")
NotificationCenter.default.removeObserver(self)
}
deinit {
print("DENINT")
}
#objc func handleUpdateTimer(notification: Notification) {
if let userInfo = notification.userInfo, let timeInSeconds = userInfo["timeInSeconds"] as? Int {
withUnsafePointer(to: &self.view) {
print("We got timeeeeee \(timeInSeconds) \($0)")
}
//do something here....
}
}
}
The issue I am having is that I am unable to remove the observers from this particular UIView when the user hits the back button and returns to another viewController.
ViewWillDisppear is called but deinit is not called. The strange thing is that if we remove subscribeToNotifications() from viewDidLoad() then the deinit is called.
The other issue is related to a memory leak. As you can see in the screenshot below, when the view does subscribe to notifications and the user leaves/re-enters the view, the memory usage increase.
Now compare that to when the subscribeToNotifications() is commented out, there is no increase in memory usage and only one instance of the viewController.
The conclusion is that there seems to be a correlation between the notification subscription creation of a new instance of the UIView hence the deinit is not being called.
I'd like to find out if there is a way we can deinitialize the view and unsubscribe from the notification.
Please let me know if you need further information. :)
I've found the removeObserver() only works if you use this version of addObserver()
notification.addObserver(self, selector:#selector(self.handleUpdateTimer), name: Notification.Name(rawValue: "TimerUpdated"), object: nil)
I'm guessing with the original version you aren't actually indicating who the observer is.
As #Spads said you can use
NotificationCenter.default.addObserver(self, selector: #selector(subscribeToNotifications), name: NSNotification.Name(rawValue: "TimerUpdate"), object: nil)
or the one you already have.
you can remove your notification by it's name or it's reference
NotificationCenter.default.removeObserver(self, name: "TimerUpdate", object: nil)
if you declared your notification at the top of your class then you can directly pass the reference of your notification to be removed in your case notification
NotificationCenter.default.removeObserver(notification)
You should store your newly added observer in a opaque object (NSObjectProtocol) and then call NotificationCenter.default.removeObserver(self.nameOfObserver)
Related
This is my first post.
I'm Japanese iOS engineer (just became this month).
I have a trouble with removeObserver method of NotificationCenter in Swift 5.
I added observer to ViewController (VC) by using closure type addObserver.
I want to remove this Observer when VC's deinitialization has called.
I wrote NotificationCenter.default.removeObserver(self) in VC's deinit method. But, this seemed not to work for me.
What's the problem???
Additionally, if my code has memory leak problem, let me know how to fix it.
Here's piece of my code.
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(forName: UIApplication.didBecomeActiveNotification, object: nil, queue: nil) { [weak self] notification in
guard let self = self else { return }
self.loadWeather(notification.object)
}
}
deinit {
print(#function)
print("ViewController died")
NotificationCenter.default.removeObserver(self)
}
}
Closure-based addObserver
If you use the closure-based variant of addObserver, the token (not self) is
the observer. The notification center has no knowledge at all about
self in this situation. The documentation is not super clear on
this.
from Twitter
Meaning it's meaningless to do: NotificationCenter.default.removeObserver(self)
The docs recommend two ways:
Normal way
Subscribe as you normally do:
let center = NSNotificationCenter.defaultCenter()
let mainQueue = NSOperationQueue.mainQueue()
self.localeChangeObserver = center.addObserverForName(NSCurrentLocaleDidChangeNotification, object: nil, queue: mainQueue) { (note) in
print("The user's locale changed to: \(NSLocale.currentLocale().localeIdentifier)")
}
Remove the observer at some point of code.
NotificationCenter.default.removeObserver(self.localeChangeObserver) e.g. through a function or in deinit
Note: You'd still need to use [weak self] to avoid retain cycles.
To avoid a retain cycle, use a weak reference to self inside the block when self contains the observer as a strong reference.
Single subscribe
Remove the observer immediately after the first time it gets a callback
let center = NSNotificationCenter.defaultCenter()
let mainQueue = NSOperationQueue.mainQueue()
var token: NSObjectProtocol?
token = center.addObserverForName("OneTimeNotification", object: nil, queue: mainQueue) { (note) in
print("Received the notification!")
center.removeObserver(token!)
}
Selector-based addObserver
If you use the selector-based add, self (there is no token) the observer. Having that said, you should avoid doing:
NotificationCenter.default.removeObserver(self)
because your code may not be the only code adding observers that involve the object. When removing an observer, remove it with the most specific detail possible. For example, if you used a name and object to register the observer, use removeObserver(_:name:object:) with the name and object.
It’s only safe to call removeObserver(something) in the deinit method, other than that don’t use it use removeObserver(_:name:object:) instead.
Calling removeObserver(self) is incorrect outside deinit, because you’d be removing all observations set for the object. Calling it inside deinit isn’t incorrect, but meaningless, because the object is to be deallocated immediately.
Set your observer object to current view controller.
From apple doc.s, object is
The object whose notifications the observer wants to receive; that is,
only notifications sent by this sender are delivered to the observer.
NotificationCenter.default.addObserver(forName: UIApplication.didBecomeActiveNotification,
object: self,
queue: nil) { [weak self] notification in
guard let self = self else { return }
self.loadWeather(notification.object)
}
Removing observer from NotificationCenter
deinit {
NotificationCenter.default.removeObserver(self)
}
ANOTHER WAY
You can also make copy of Notification Observer object and remove it from NotificationCenter in deinit.
let notificationCenter = NotificationCenter.default
var loadWeatherObserver: NSObjectProtocol?
override func viewDidLoad() {
super.viewDidLoad()
loadWeatherObserver = notificationCenter.addObserver(forName: UIApplication.didBecomeActiveNotification,
object: nil,
queue: nil) { [weak self] notification in
guard let self = self else { return }
self.loadWeather(notification.object)
}
}
deinit {
if (loadWeatherObserver != nil) {
notificationCenter.removeObserver(loadWeatherObserver!)
}
}
I am new to ios programming, I wanted to register notification center in the class, not in the view controller, I want to send some action from one view controller this custom class receives that action and it performs some view controller navigation.I wanted to have custom notification center in ios.
code:
NotificationCenter.default.post(name: Notification.Name(rawValue: "key"), object: nil)
class MainReceiver: NotificationCenter
{
override func post(name aName: NSNotification.Name, object anObject: Any?)
{
print("coming here")
}
}
Here you have snipped code:
class MainReceiver {
init() {
NotificationCenter.default.addObserver(self, selector: #selector(handleMethod(_:)), name: NSNotification.Name(rawValue: "Notification_Name"), object: nil)
}
deinit {
NotificationCenter.default.removeObserver(self)
}
#objc func handleMethod(_ notification: Notification) {
// handle
}
}
From Apple's NSNotificationCenter documentation:
Each running Cocoa program has a default notification center. You typically don’t create your own.
I'm not sure why you think you want to create your own notification center, but trust me, you don't.
However, you can easily subscribe an object (an instance of a custom class, like you say you want to use) to notifications:
// let object = Whatever()
NotificationCenter.default.addObserver(object, selector: #selector(didReceive(notification:)), name: NSNotification.Name(rawValue: "key"), object: nil)
// object's didReceive(notification:) function will now be called when a notification with the specified name is posted. This can be posted from anywhere.
A while back, the function had to be decorated with the #objc attribute. I'm not sure if that's still the case, but if so, you'd use #objc func didReceive(notification: Notification) as your declaration in the receiving class.
If I understand your question correctly I think what you are looking for is the blocked based variant for the NotificationCenter.
You can find it in the official docs.
Example code from the docs:
let center = NSNotificationCenter.defaultCenter()
let mainQueue = NSOperationQueue.mainQueue()
self.localeChangeObserver = center.addObserverForName(NSCurrentLocaleDidChangeNotification, object: nil, queue: mainQueue) { (note) in
print("The user's locale changed to: \(NSLocale.currentLocale().localeIdentifier)")
I have a class that accepts accelerometer data and posts it in a notification like so:
func notify(accel: accelPoint){
NotificationCenter.default.post(name: Notification.Name("newRawData"), object: nil)
}
And two objects set up to observe this, the first being a viewController:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(FirstViewController.newRawData), name: Notification.Name("newRawData"), object: nil)
Which calls the function:
func newRawData(notification: NSNotification){ ...
This works just fine.
The other observer is in a regular Swift class, instantiated in the app delegate. (I have tried doing this before and after creating the notifying class):
init(){
NotificationCenter.default.addObserver(self, selector: #selector(FilterManager.newRawData), name: Notification.Name("newRawData"), object: nil)
}
Which should call the function below but for some reason it does not.
#objc func newRawData(){
print("WHYYY")
}
The name this class is correct, and I have seen the the observer is being registered and the notifications are being posted so why isn't this class being notified like the other?
Also, why do I have to expose the newRawData function in the second class to objective-C but not the newRawData in the viewController class?
did you referenced FilterManager class in your AppDelegate? if not add this code in you AppDelegate class. also you can make FilterManger singleton to solve this problem.
var filterManger = FilterManager()
My ViewController.swift
func startTimer() {
timer = NSTimer().scheduleTimerWithTimerInvterval(1.0,target: self,selctor: Selector("couting"),userinfo: nil, repeats: true)
}
func pauseTimer() {
timer.invalidate()
println("pausing timer")
}
and this is appDelegate.swift
func applicateWillResignActive(application: UIApplication) {
viewController().pauseTimer()
println("closing app")
}
It is printing pausing timer and closing app but when I open again I see it never paused. How do I do it correctly?
You have to set an observer listening to when the application did enter background. Add the below line in your ViewController's viewDidLoad() method.
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("myObserverMethod:"), name:UIApplicationDidEnterBackgroundNotification, object: nil)
Add the below function to receive the notification.
func myObserverMethod(notification : NSNotification) {
println("Observer method called")
//You may call your action method here, when the application did enter background.
//ie., self.pauseTimer() in your case.
}
Happy Coding !!!
Updated Answer for Swift 5:
NotificationCenter.default.addObserver
(self,
selector: #selector(myObserverMethod),
name:UIApplication.didEnterBackgroundNotification, object: nil)
#objc func myObserverMethod() {
print("Write Your Code Here")
}
Accepted answer by #Suresh in Swift 3
Set an observer listening to when the application did enter background in your ViewController's viewDidLoad() method.
NotificationCenter.default.addObserver(self, selector: #selector(myObserverMethod), name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
Add the below function to receive the notification.
func myObserverMethod(notification : NSNotification) {
print("Observer method called")
//You may call your action method here, when the application did enter background.
//ie., self.pauseTimer() in your case.
}
Updated Answer for Swift 4:
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(myObserverMethod), name:NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
}
#objc func myObserverMethod() {
// Call your action method here, when the application did enter background.
}
You are creating a new object and calling pauseTimer() on it:
viewController().pauseTimer() // This line causes issue viewController(), creates a new instance
Instead of creating new object, either you should pass that instance to AppDelegate and call pauseTimer() on existing object or Listen for UIApplicationDidEnterBackgroundNotification notification in your view controller class and pause timer from there.
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
}