How do you add an observer in Swift to the default notification center? I'm trying to port this line of code that sends a notification when the battery level changes.
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(batteryLevelChanged:) name:UIDeviceBatteryLevelDidChangeNotification object:nil];
Swift 4.0 & Xcode 9.0+:
Send(Post) Notification:
NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil)
OR
NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil, userInfo: ["Renish":"Dadhaniya"])
Receive(Get) Notification:
NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
Function-Method handler for received Notification:
#objc func methodOfReceivedNotification(notification: Notification) {}
Swift 3.0 & Xcode 8.0+:
Send(Post) Notification:
NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: nil)
Receive(Get) Notification:
NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
Method handler for received Notification:
func methodOfReceivedNotification(notification: Notification) {
// Take Action on Notification
}
Remove Notification:
deinit {
NotificationCenter.default.removeObserver(self, name: Notification.Name("NotificationIdentifier"), object: nil)
}
Swift 2.3 & Xcode 7:
Send(Post) Notification
NSNotificationCenter.defaultCenter().postNotificationName("NotificationIdentifier", object: nil)
Receive(Get) Notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name:"NotificationIdentifier", object: nil)
Method handler for received Notification
func methodOfReceivedNotification(notification: NSNotification){
// Take Action on Notification
}
For historic Xcode versions...
Send(Post) Notification
NSNotificationCenter.defaultCenter().postNotificationName("NotificationIdentifier", object: nil)
Receive(Get) Notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: "methodOfReceivedNotification:", name:"NotificationIdentifier", object: nil)
Remove Notification
NSNotificationCenter.defaultCenter().removeObserver(self, name: "NotificationIdentifier", object: nil)
NSNotificationCenter.defaultCenter().removeObserver(self) // Remove from all notifications being observed
Method handler for received Notification
func methodOfReceivedNotification(notification: NSNotification) {
// Take Action on Notification
}
Annotate either the class or the target method with #objc
#objc private func methodOfReceivedNotification(notification: NSNotification) {
// Take Action on Notification
}
// Or
dynamic private func methodOfReceivedNotification(notification: NSNotification) {
// Take Action on Notification
}
It's the same as the Objective-C API, but uses Swift's syntax.
Swift 4.2 & Swift 5:
NotificationCenter.default.addObserver(
self,
selector: #selector(self.batteryLevelChanged),
name: UIDevice.batteryLevelDidChangeNotification,
object: nil)
If your observer does not inherit from an Objective-C object, you must prefix your method with #objc in order to use it as a selector.
#objc private func batteryLevelChanged(notification: NSNotification){
//do stuff using the userInfo property of the notification object
}
See NSNotificationCenter Class Reference, Interacting with Objective-C APIs
A nice way of doing this is to use the addObserver(forName:object:queue:using:) method rather than the addObserver(_:selector:name:object:) method that is often used from Objective-C code. The advantage of the first variant is that you don't have to use the #objc attribute on your method:
func batteryLevelChanged(notification: Notification) {
// do something useful with this information
}
let observer = NotificationCenter.default.addObserver(
forName: NSNotification.Name.UIDeviceBatteryLevelDidChange,
object: nil, queue: nil,
using: batteryLevelChanged)
and you can even just use a closure instead of a method if you want:
let observer = NotificationCenter.default.addObserver(
forName: NSNotification.Name.UIDeviceBatteryLevelDidChange,
object: nil, queue: nil) { _ in print("🔋") }
You can use the returned value to stop listening for the notification later:
NotificationCenter.default.removeObserver(observer)
There used to be another advantage in using this method, which was that it doesn't require you to use selector strings which couldn't be statically checked by the compiler and so were fragile to breaking if the method is renamed, but Swift 2.2 and later include #selector expressions that fix that problem.
Declare a notification name
extension Notification.Name {
static let purchaseDidFinish = Notification.Name("purchaseDidFinish")
}
You can add observer in two ways:
Using Selector
NotificationCenter.default.addObserver(self, selector: #selector(myFunction), name: .purchaseDidFinish, object: nil)
#objc func myFunction(notification: Notification) {
print(notification.object ?? "") //myObject
print(notification.userInfo ?? "") //[AnyHashable("key"): "Value"]
}
or using block
NotificationCenter.default.addObserver(forName: .purchaseDidFinish, object: nil, queue: nil) { [weak self] (notification) in
guard let strongSelf = self else {
return
}
strongSelf.myFunction(notification: notification)
}
func myFunction(notification: Notification) {
print(notification.object ?? "") //myObject
print(notification.userInfo ?? "") //[AnyHashable("key"): "Value"]
}
Post your notification
NotificationCenter.default.post(name: .purchaseDidFinish, object: "myObject", userInfo: ["key": "Value"])
from iOS 9 and OS X 10.11. It is no longer necessary for an
NSNotificationCenter observer to un-register itself when being
deallocated. more info
For a block based implementation you need to do a weak-strong dance if you want to use self inside the block. more info
Block based observers need to be removed more info
let center = NSNotificationCenter.defaultCenter()
center.removeObserver(self.localeChangeObserver)
Swift 3.0 in Xcode 8
Swift 3.0 has replaced many "stringly-typed" APIs with struct "wrapper types", as is the case with NotificationCenter. Notifications are now identified by a struct Notfication.Name rather than by String. See the Migrating to Swift 3 guide.
Previous usage:
// Define identifier
let notificationIdentifier: String = "NotificationIdentifier"
// Register to receive notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name: notificationIdentifier, object: nil)
// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationIdentifier, object: nil)
New Swift 3.0 usage:
// Define identifier
let notificationName = Notification.Name("NotificationIdentifier")
// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification), name: notificationName, object: nil)
// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)
All of the system notification types are now defined as static constants on Notification.Name; i.e. .UIDeviceBatteryLevelDidChange, .UIApplicationDidFinishLaunching, .UITextFieldTextDidChange, etc.
You can extend Notification.Name with your own custom notifications in order to stay consistent with the system notifications:
// Definition:
extension Notification.Name {
static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}
// Usage:
NotificationCenter.default.post(name: .yourCustomNotificationName, object: nil)
In Swift 5
Let's say if want to Receive Data from ViewControllerB to
ViewControllerA
ViewControllerA (Receiver)
import UIKit
class ViewControllerA: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
//MARK: - - - - - Code for Passing Data through Notification Observer - - - - -
// add observer in controller(s) where you want to receive data
NotificationCenter.default.addObserver(self, selector: #selector(self.methodOfReceivedNotification(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil)
}
//MARK: - - - - - Method for receiving Data through Post Notificaiton - - - - -
#objc func methodOfReceivedNotification(notification: Notification) {
print("Value of notification : ", notification.object ?? "")
}
}
ViewControllerB (Sender)
import UIKit
class ViewControllerB: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
//MARK: - - - - - Set data for Passing Data Post Notification - - - - -
let objToBeSent = "Test Message from Notification"
NotificationCenter.default.post(name: Notification.Name("NotificationIdentifier"), object: objToBeSent)
}
}
Pass Data using NSNotificationCenter
You can also pass data using NotificationCentre in swift 3.0 and NSNotificationCenter in swift 2.0.
Swift 2.0 Version
Pass info using userInfo which is a optional Dictionary of type [NSObject : AnyObject]?
let imageDataDict:[String: UIImage] = ["image": image]
// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationName, object: nil, userInfo: imageDataDict)
// Register to receive notification in your class
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: notificationName, object: nil)
// handle notification
func showSpinningWheel(notification: NSNotification) {
if let image = notification.userInfo?["image"] as? UIImage {
// do something with your image
}
}
Swift 3.0 Version
The userInfo now takes [AnyHashable:Any]? as an argument, which we provide as a dictionary literal in Swift
let imageDataDict:[String: UIImage] = ["image": image]
// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: imageDataDict)
// `default` is now a property, not a method call
// Register to receive notification in your class
NotificationCenter.default.addObserver(self, selector: #selector(self.showSpinningWheel(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)
// handle notification
func showSpinningWheel(_ notification: NSNotification) {
if let image = notification.userInfo?["image"] as? UIImage {
// do something with your image
}
}
Source pass data using NotificationCentre(swift 3.0) and NSNotificationCenter(swift 2.0)
Swift 5 Notification Observer
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelChanged), name: UIDevice.batteryLevelDidChangeNotification, object: nil)
}
#objc func batteryLevelChanged(notification : NSNotification){
//do here code
}
override func viewWillDisappear(_ animated: Bool) {
NotificationCenter.default.removeObserver(self, name: UIDevice.batteryLevelDidChangeNotification, object: nil)
}
I'm able to do one of the following to successfully use a selector - without annotating anything with #objc:
NSNotificationCenter.defaultCenter().addObserver(self,
selector:"batteryLevelChanged:" as Selector,
name:"UIDeviceBatteryLevelDidChangeNotification",
object:nil)
OR
let notificationSelector: Selector = "batteryLevelChanged:"
NSNotificationCenter.defaultCenter().addObserver(self,
selector: notificationSelector,
name:"UIDeviceBatteryLevelDidChangeNotification",
object:nil)
My xcrun version shows Swift 1.2, and this works on Xcode 6.4 and Xcode 7 beta 2 (which I thought would be using Swift 2.0):
$xcrun swift --version
Apple Swift version 1.2 (swiftlang-602.0.53.1 clang-602.0.53)
This is very simple example of custom notification observer and post
Add Notification Observer
NotificationCenter.default.addObserver(self, selector: #selector(myFunction), name: Notification.Name("CustomeNotificationName"), object: nil)
Add Selector and handle Observer call
#objc func myFunction(notification: Notification) {
//Write you code
}
Post Notification(Observer) when it is required.
NotificationCenter.default.post(name: NSNotification.Name("CustomeNotificationName"), object: "Object", userInfo: ["key":"Value"])
Notes:- Make user when you leave screen you need to remove observer. e.g.
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NotificationCenter.default.removeObserver(self);
}
Create an objc function which you want to execute when notification is called.
#objc func reloadNotification(_ notification: Notification) {
tblview.reloadData()
}
Add the notification observer in view did load.
NotificationCenter.default.addObserver(self, selector:#selector(reloadNotification(_:)), name: Notification.Name("reloadSideMenuDataNS"),object: nil)
post your notification where you want to call the function.
NotificationCenter.default.post(name: Notification.Name("reloadSideMenuDataNS"), object: nil)
you can remove your notification in view did disappear with below.
NotificationCenter.default.removeObserver(self, name: Notification.Name("reloadSideMenuDataNS"), object: nil)
In swift 2.2 - XCode 7.3, we use #selector for NSNotificationCenter
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(rotate), name: UIDeviceOrientationDidChangeNotification, object: nil)
We should remove notification also.
Ex.
deinit
{
NotificationCenter.default.removeObserver(self, name:NSNotification.Name(rawValue: "notify"), object: nil)
}
In swift 3, Xcode 8.2:- checking battery state level
//Add observer
NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: NSNotification.Name.UIDeviceBatteryStateDidChange, object: nil)
//Fired when battery level changes
func batteryStateDidChange(notification: NSNotification){
//perform manipulation here
}
NSNotificationCenter add observer syntax in Swift 4.0 for iOS 11
NotificationCenter.default.addObserver(self, selector: #selector(keyboardShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
This is for keyboardWillShow notification name type. Other type can be selected from the available option
the Selector is of type #objc func which handle how the keyboard will show ( this is your user function )
Swift 5 & Xcode 10.2:
NotificationCenter.default.addObserver(
self,
selector: #selector(batteryLevelDidChangeNotification),
name: UIDevice.batteryLevelDidChangeNotification,
object: nil)
Related
i am trying to post notification NotificationCenter from appdelegate and receive notification in another view but notification not received.
Post notification :-
func xmppStream(_ sender: XMPPStream, didReceive message: XMPPMessage)
{
print("did receive message isss-->\(message)")
NotificationCenter.default.post(name: Notification.Name("MessageReceived"), object: message)
}
Received Notification in viewdidload :-
NotificationCenter.default.addObserver(self, selector: #selector(self.messagereceived(notification:)), name: Notification.Name("MessageReceived"), object: nil)
Method :-
#objc func messagereceived(notification:Notification)
{
let message = notification.object as? XMPPMessage
print("chat conversion message is----->\(message)")
}
My "messagereceived" Method not called.
so any one have solution related to this then please help me.
Thanks in advance.
Change the notification post from
NotificationCenter.default.post(name: Notification.Name("MessageReceived"), object: message)
to
NotificationCenter.default.post(Notification(name: Notification.Name(rawValue: "MessageReceived"),object: message))
and the observer from
NotificationCenter.default.addObserver(self, selector: #selector(self.messagereceived(notification:)), name: Notification.Name("MessageReceived"), object: nil)
to
NotificationCenter.default.addObserver(self, selector: #selector(self.messagereceived(notification:)), name: NSNotification.Name(rawValue: "MessageReceived"), object: nil)
In my case i can't get NotificationCenter in some situation in my app .
and problem was that using
NotificationCenter.default.addObserver(self, selector: #selector(btnRegister(_:)), name: Notification.Name(rawValue: "btnRegister"), object: nil)
in my viewDidLoad() func, And when i set above code in my viewWillAppear() func, that's work perfectly.
According to your code logic , move above code to other func or other section of your code and try to fix your problem.
This question already has answers here:
NSNotificationCenter addObserver in Swift
(16 answers)
Closed 6 years ago.
I'm learning Swift 3 and I'm trying to using NSNotificationCenter. Here is my code:
func savePost(){
let postData = NSKeyedArchiver.archivedData(withRootObject: _loadedpost)
UserDefaults.standard().object(forKey: KEY_POST)
}
func loadPost(){
if let postData = UserDefaults.standard().object(forKey: KEY_POST) as? NSData{
if let postArray = NSKeyedUnarchiver.unarchiveObject(with: postData as Data) as? [Post]{
_loadedpost = postArray
}
}
//codeerror
NotificationCenter.default().post(NSNotification(name: "loadedPost" as NSNotification.Name, object: nil) as Notification)
}
and this is the observer:
override func viewDidLoad() {
super.viewDidLoad()
//codeerorr
NotificationCenter.default().addObserver(self, selector: Selector(("onPostLoaded")), name: "loadedPost", object: nil)
}
func numberOfSections(in tableView: UITableView) -> Int {
return 1
}
It always gives me the error "signal SIGBRT". When I try to change the name in the observer, it's not an error, but obviously it didn't show anything. How do I fix this?
Swift 3 & 4
Swift 3, and now Swift 4, have replaced many "stringly-typed" APIs with struct "wrapper types", as is the case with NotificationCenter. Notifications are now identified by a struct Notfication.Name rather than by String. For more details see the now legacy Migrating to Swift 3 guide
Swift 2.2 usage:
// Define identifier
let notificationIdentifier: String = "NotificationIdentifier"
// Register to receive notification
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification(_:)), name: notificationIdentifier, object: nil)
// Post a notification
NSNotificationCenter.defaultCenter().postNotificationName(notificationIdentifier, object: nil)
Swift 3 & 4 usage:
// Define identifier
let notificationName = Notification.Name("NotificationIdentifier")
// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(YourClassName.methodOfReceivedNotification), name: notificationName, object: nil)
// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)
// Stop listening notification
NotificationCenter.default.removeObserver(self, name: notificationName, object: nil)
All of the system notification types are now defined as static constants on Notification.Name; i.e. .UIApplicationDidFinishLaunching, .UITextFieldTextDidChange, etc.
You can extend Notification.Name with your own custom notifications in order to stay consistent with the system notifications:
// Definition:
extension Notification.Name {
static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}
// Usage:
NotificationCenter.default.post(name: .yourCustomNotificationName, object: nil)
Swift 4.2 usage:
Same as Swift 4, except now system notifications names are part of UIApplication. So in order to stay consistent with the system notifications you can extend UIApplication with your own custom notifications instead of Notification.Name :
// Definition:
UIApplication {
public static let yourCustomNotificationName = Notification.Name("yourCustomNotificationName")
}
// Usage:
NotificationCenter.default.post(name: UIApplication.yourCustomNotificationName, object: nil)
Notifications appear to have changed again (October 2016).
// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(yourClass.yourMethod), name: NSNotification.Name(rawValue: "yourNotificatioName"), object: nil)
// Post notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "yourNotificationName"), object: nil)
For all struggling around with the #selector in Swift 3 or Swift 4, here a full code example:
// WE NEED A CLASS THAT SHOULD RECEIVE NOTIFICATIONS
class MyReceivingClass {
// ---------------------------------------------
// INIT -> GOOD PLACE FOR REGISTERING
// ---------------------------------------------
init() {
// WE REGISTER FOR SYSTEM NOTIFICATION (APP WILL RESIGN ACTIVE)
// Register without parameter
NotificationCenter.default.addObserver(self, selector: #selector(MyReceivingClass.handleNotification), name: .UIApplicationWillResignActive, object: nil)
// Register WITH parameter
NotificationCenter.default.addObserver(self, selector: #selector(MyReceivingClass.handle(withNotification:)), name: .UIApplicationWillResignActive, object: nil)
}
// ---------------------------------------------
// DE-INIT -> LAST OPTION FOR RE-REGISTERING
// ---------------------------------------------
deinit {
NotificationCenter.default.removeObserver(self)
}
// either "MyReceivingClass" must be a subclass of NSObject OR selector-methods MUST BE signed with '#objc'
// ---------------------------------------------
// HANDLE NOTIFICATION WITHOUT PARAMETER
// ---------------------------------------------
#objc func handleNotification() {
print("RECEIVED ANY NOTIFICATION")
}
// ---------------------------------------------
// HANDLE NOTIFICATION WITH PARAMETER
// ---------------------------------------------
#objc func handle(withNotification notification : NSNotification) {
print("RECEIVED SPECIFIC NOTIFICATION: \(notification)")
}
}
In this example we try to get POSTs from AppDelegate (so in AppDelegate implement this):
// ---------------------------------------------
// WHEN APP IS GOING TO BE INACTIVE
// ---------------------------------------------
func applicationWillResignActive(_ application: UIApplication) {
print("POSTING")
// Define identifiyer
let notificationName = Notification.Name.UIApplicationWillResignActive
// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)
}
I think it has changed again.
For posting this works in Xcode 8.2.
NotificationCenter.default.post(Notification(name:.UIApplicationWillResignActive)
I use Core Spotlight, and I use UIPageController as RootViewController and several UIViewControllers. Every controller has UIView I drawing a circle of information in there. When I slide between controllers and open new controller I sent NSNotification from current UIViewController to current UIView which is located on current UIViewController. I sent NSNotification that so turn on NSTimer in UIView for updating of information. It works is fine when I just open the app. My problem is when I find infromation from the app in spotlight search and open needed controller from spotlight search NSNotification doesn't sent. I tried several different methods and I cannot to find how I can to make it. Please tell me how can I make it?
UPDATE I also tried singleton pattern for NSNotificationCenter but it also didn't help me.
UPDATE I tried write Selector as notificationCenter.addObserver(self, selector: Selector(turnOnMemoryTimer()), name: "turnOnMemoryArc", object: nil)
and it works when I launch app from spotlight search but it doesn't work when I just launch the app. For any help on this matter thanks!
I also tried to send notification from AppDelegate but it also didn't work
switch startIndex {
case 1:
notificatioCenter.postNotificationName("turnOnCPUTimer", object: nil)
default: break
}
UIViewController
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(true)
if GlobalTimer.sharedInstance.controllerTimer != nil {
GlobalTimer.sharedInstance.controllerTimer.invalidate()
GlobalTimer.sharedInstance.viewTimer.invalidate()
}
GlobalTimer.sharedInstance.controllerTimer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "showMemory", userInfo: nil, repeats: true)
// notifications
notificationCenter.postNotificationName("turnOnMemoryArc", object: nil) // this message doesn't sent
if UIDevice.currentDevice().userInterfaceIdiom == .Pad {
notificationCenter.postNotificationName("checkMemoryOrientation", object: nil)
notificationCenter.addObserver(self, selector: "changeMemoryOrientation", name: UIDeviceOrientationDidChangeNotification, object: nil)
}
}
UIView
// MARK: - var and let
var arc = Arc()
let notificationCenter = NSNotificationCenter.defaultCenter()
var boolForMemoryArc = false
override func drawRect(rect: CGRect) {
if boolForMemoryArc == false {
drawMemoryArc()
boolForMemoryArc = true
}
notificationCenter.addObserver(self, selector: "turnOnMemoryTimer", name: "turnOnMemoryArc", object: nil)
notificationCenter.addObserver(self, selector: "changedMemoryOrientation", name: "checkMemoryOrientation", object: nil)
}
func turnOnMemoryTimer() {
if GlobalTimer.sharedInstance.viewTimer != nil {
GlobalTimer.sharedInstance.viewTimer.invalidate()
}
GlobalTimer.sharedInstance.viewTimer = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: "drawMemoryArc", userInfo: nil, repeats: true)
}
I had a similiar issue and solved it like this:
notificationCenter.addObserver(self, selector: "turnOnMemoryTimer:", name: "turnOnMemoryArc", object: nil)
Receive AnyObject:
func turnOnMemoryTimer(notification: AnyObject) {
}
This needed change happened "spontaneous" the normal code was working for months.
I think you need to add the NSNotification as parameter to the function you're calling. So, two tweeks:
notificationCenter.addObserver(self, selector: "turnOnMemoryTimer:", name: "turnOnMemoryArc", object: nil)
and
func turnOnMemoryTimer(notification: NSNotification) {
// function body
}
I am looking for a function which is called on a UIViewController when the application exits.
I tried it out with viewWillDisappear and with applicationWillTerminate but nothing works.
I want to save my settings from the UIViewController in this function.
Like #Jeff said, but
In Swift 3:
override func viewDidLoad () {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(suspending), name: NSNotification.Name.UIApplicationWillResignActive, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(suspending), name: NSNotification.Name.UIApplicationWillTerminate, object: nil)
}
func suspending () {
print("suspending...")
}
UIApplicationWillResignActive happens when the app is swapped out, while
UIApplicationWillTerminate is triggered when exiting, such as when the Home button is pressed.
You need to register for notifications to know when the appropriate calls are made as an app terminates.
NSNotificationCenter .defaultCenter() .addObserver(self, selector: Selector("callBack"), name: UIApplicationWillResignActiveNotification, object: nil)
NSNotificationCenter .defaultCenter() .addObserver(self, selector: Selector("callBack"), name: UIApplicationWillTerminateNotification, object: nil)
func callback() {
// Save your settings
}
Remember to remove the observers in viewWillDisappear:
override func viewWillDisappear(animated: Bool) {
super.viewWillDisappear(animated)
NSNotificationCenter .defaultCenter() .removeObserver(self)
}
you can call deinit inside the ViewController
deinit {
deleteUnsavedPhotoFromServer()
}
Swift 5.5
Use For App Enter Background
NotificationCenter.default.addObserver(self, selector: #selector(appResignActiveNotify), name: UIApplication.willResignActiveNotification, object: nil)
#objc func appResignActiveNotify() {
//called when App enter background
}
For App Terminate
NotificationCenter.default.addObserver(self, selector: #selector(appTerminateNotify), name: UIApplication.willTerminateNotification, object: nil)
#objc func appTerminateNotify() {
//called when Terminate
}
I have the UIApplicationDelegate protocol in my main AppDelegate.m class, with the applicationDidBecomeActive method defined.
I want to call a method when the application returns from the background, but the method is in another view controller. How can I check which view controller is currently showing in the applicationDidBecomeActive method and then make a call to a method within that controller?
Any class in your application can become an "observer" for different notifications in the application. When you create (or load) your view controller, you'll want to register it as an observer for the UIApplicationDidBecomeActiveNotification and specify which method that you want to call when that notification gets sent to your application.
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(someMethod:)
name:UIApplicationDidBecomeActiveNotification object:nil];
Don't forget to clean up after yourself! Remember to remove yourself as the observer when your view is going away:
[[NSNotificationCenter defaultCenter] removeObserver:self
name:UIApplicationDidBecomeActiveNotification
object:nil];
More information about the Notification Center.
Swift 3, 4 Equivalent:
adding observer
NotificationCenter.default.addObserver(self,
selector: #selector(applicationDidBecomeActive),
name: .UIApplicationDidBecomeActive, // UIApplication.didBecomeActiveNotification for swift 4.2+
object: nil)
removing observer
NotificationCenter.default.removeObserver(self,
name: .UIApplicationDidBecomeActive, // UIApplication.didBecomeActiveNotification for swift 4.2+
object: nil)
callback
#objc func applicationDidBecomeActive() {
// handle event
}
Swift 2 Equivalent:
let notificationCenter = NSNotificationCenter.defaultCenter()
// Add observer:
notificationCenter.addObserver(self,
selector:Selector("applicationWillResignActiveNotification"),
name:UIApplicationWillResignActiveNotification,
object:nil)
// Remove observer:
notificationCenter.removeObserver(self,
name:UIApplicationWillResignActiveNotification,
object:nil)
// Remove all observer for all notifications:
notificationCenter.removeObserver(self)
// Callback:
func applicationWillResignActiveNotification() {
// Handle application will resign notification event.
}
Swift 5
fileprivate func addObservers() {
NotificationCenter.default.addObserver(self,
selector: #selector(applicationDidBecomeActive),
name: UIApplication.didBecomeActiveNotification,
object: nil)
}
fileprivate func removeObservers() {
NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
}
#objc fileprivate func applicationDidBecomeActive() {
// here do your work
}
Swift 4.2
Add observer-
NotificationCenter.default.addObserver(self, selector: #selector(handleEvent), name: UIApplication.didBecomeActiveNotification, object: nil)
Remove observer-
NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
Handle Event-
#objc func handleEvent() {
}
With Swift 4, Apple advises via a new compiler warning that we avoid the use of #selector in this scenario. The following is a much safer way to accomplish this:
First, create a variable that will hold the observer instance (that will be used to cancel it):
var didBecomeActiveObserver: NSObjectProtocol
Then create a lazy var that can be used by the notification:
lazy var didBecomeActive: (Notification) -> Void = { [weak self] _ in
// Do stuff
}
If you require the actual notification be included, just replace the _ with notification.
Next, we set up the notification to observe for the app becoming active.
func setupObserver() {
didBecomeActiveObserver = NotificationCenter.default.addObserver(
forName: UIApplication.didBecomeActiveNotification,
object: nil,
queue:.main,
using: didBecomeActive)
}
The big change here is that instead of calling a #selector, we now call the var created above. This can eliminate situations where you get invalid selector crashes.
Finally, we remove the observer.
func removeObserver() {
NotificationCenter.default.removeObserver(didBecomeActiveObserver)
}
Swift 5 version:
NotificationCenter.default.addObserver(self,
selector: #selector(loadData),
name: UIApplication.didBecomeActiveNotification,
object: nil)
Removing the observer is no longer required in iOS 9 and later.
In Swift 5
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(applicationWillResignActive), name: UIApplication.willResignActiveNotification, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NotificationCenter.default.removeObserver(self, name: UIApplication.willResignActiveNotification, object: nil)
NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
}
#objc private func applicationWillResignActive() {
}
#objc private func applicationDidBecomeActive() {
}
The Combine way:
import Combine
var cancellables = Set<AnyCancellable>()
NotificationCenter.default.publisher(for: UIApplication.didBecomeActiveNotification)
.sink { notification in
// do stuff
}.store(in: &cancellables)
If any of you is using SwiftUI:
.onReceive(NotificationCenter.default.publisher(
for: UIApplication.didBecomeActiveNotification)) { _ in
print("DID BECOME ACTIVE")
}
)
Cleaner Swift 5+ solution
Add the observer to init or viewDidLoad:
NotificationCenter.default.addObserver(self,
selector: #selector(appDidBecomeActive),
name: UIApplication.didBecomeActiveNotification,
object: nil)
You don't need to remove the observer as other answers suggest. It will be done automatically.
#objc private func appDidBecomeActive() {
// do your magic
}
For Swift5 MacOS, you need to use NSApplication instead of UIApplication.
NotificationCenter.default.addObserver(self,
selector: #selector(applicationDidBecomeActive),
name: (NSApplication.didBecomeActiveNotification),
object: nil)
}