I am trying to learn how to use NSNotification for a project I am working on, and since I have never used it before, I am first trying to learn how to use it first, however; every time I try to follow a youtube tutorial or a tutorial found online my code doesn't seem to be working. Also, when trying to debug the issue, it is showing the observer part of the code isn't going inside the #obj c function. Below is my code showing how it is being used to post and observe a notification.
extension Notification.Name {
static let notifyId = Notification.Name("NotifyTest")
}
ViewController.swift
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
var test: ObserverObj = ObserverObj(observerLblText: "Observing")
#IBAction func notifyObserver(_ sender: Any) {
let vc = storyboard?.instantiateViewController(identifier: "ObserverVC")
vc?.modalPresentationStyle = .fullScreen
guard let vcL = vc else {
return
}
NotificationCenter.default.post(name: .notifyId, object: nil)
self.navigationController?.pushViewController(vcL, animated: true)
}
}
NotificationTestViewController.swift
import UIKit
class NotificationTestViewController: UIViewController {
#IBOutlet weak var observerLbl: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(observingFunc(notification:)), name: .notifyId, object: nil)
// Do any additional setup after loading the view.
}
#objc func observingFunc(notification: Notification) {
observerLbl.text = "notifying"//text.test.observerLblText
}
Can someone help me and let me know where I am going wrong as I've been trying for 2 days.
The notification is sent before the observer is added, that means viewDidLoad in the destination controller is executed after the post line in the source view controller.
Possible solutions are :
Override init(coder in the destination controller and add the observer there.
required init?(coder: NSCoder) {
super.init(coder: coder)
NotificationCenter.default.addObserver(self, selector: #selector(observingFunc), name: .notifyId, object: nil)
}
If init(coder is not called override init()
Add the observer before posting the notification (this solution is only for education purpose)
#IBAction func notifyObserver(_ sender: Any) {
guard let vcL = storyboard?.instantiateViewController(identifier: "ObserverVC") as? NotificationTestViewController else { return }
vcL.modalPresentationStyle = .fullScreen
NotificationCenter.default.addObserver(vcL, selector: #selector(NotificationTestViewController.observingFunc), name: .notifyId, object: nil)
self.navigationController?.pushViewController(vcL, animated: true)
NotificationCenter.default.post(name: .notifyId, object: nil)
}
However in practice you are strongly discouraged from sending a notification to a destination you have the reference to.
The reason is that when you send out a notification, your NotificationTestViewController has not yet called the viewdidload method
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
var test: ObserverObj = ObserverObj(observerLblText: "Observing")
#IBAction func notifyObserver(_ sender: Any) {
let vc = storyboard?.instantiateViewController(identifier: "ObserverVC")
vc?.modalPresentationStyle = .fullScreen
guard let vcL = vc else {
return
}
self.navigationController?.pushViewController(vcL, animated: true)
NotificationCenter.default.post(name: .notifyId, object: nil)
}
}
Related
I'm trying to send a notification on changing the navigation stack update. But it's not triggered. Here is my code. I have a requirement to change the root view controller on button action. I'm trying the below code, but it's not working for me.
import UIKit
class SecondViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func replaceThirdViewControllerAsNavigationRoot() {
let nc = NotificationCenter.default
nc.post(name: Notification.Name("Notify"), object: nil)
self.navigationController?.viewControllers = [ThirdViewController.instance()]
}
}
class ThirdViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let nc = NotificationCenter.default
nc.addObserver(self, selector: #selector(userLoggedIn), name: Notification.Name("Notify"), object: nil)
}
#objc func userLoggedIn() {
print("-----")
}
}
extension UIViewController {
static func instance<T: UIViewController>() -> T {
let name = String(describing: self)
guard let controller = UIStoryboard.main.instantiateViewController(withIdentifier: name) as? T else {
fatalError("ViewController '\(name)' is not of the expected class \(T.self).")
}
return controller
}
}
extension UIStoryboard {
static var main: UIStoryboard {
return UIStoryboard.init(name: "Main", bundle: nil)
}
}
Thanks in advance.
The sequence of event is wrong. When you post a notification, you need to make sure that an observer already exists, otherwise the notification will be discarded.
In other words: make sure that
nc.addObserver(self, selector: #selector(userLoggedIn), name: Notification.Name("Notify"), object: nil)
runs before
nc.post(name: Notification.Name("Notify"), object: nil)
I have a problem when I try to pass an array from a UITableView to another one using NotificationCenter Design Pattern (because I don't have a segue between this 2 UIViewControllers). I don't know what I'm doing wrong but I don't receive any data in my second view controller.
My functions looks like this:
* First VC - The Sender Controller (From where I send data) *
class ProductsViewController: UIViewController{
var selectedProductsArray = [Product]()
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// Implement Notification Design Pattern to send data
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "productsToLoad"), object: selectedProductsArray)
print(selectedProductsArray) // Here I have some data in this array (Photo here: https://ibb.co/k8hoEy)
}
* Second ViewController - The Receiver Controller (Where I will receive the data) *
class CartViewController: UIViewController {
var productsInCartArray = [Product]()
// We retrieve data from "selectedProductsArray" and we append all the products into "productsInCartArray"
#objc func notificationRecevied(notification: Notification) {
productsInCartArray = notification.object as! [Product]
print(productsInCartArray)
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// Add observer to watch when something was changed in "selectedProductsArray"
NotificationCenter.default.addObserver(self, selector: #selector(notificationRecevied(notification:)), name: NSNotification.Name(rawValue: "productsToLoad"), object: nil)
print(productsInCartArray) // Output: []
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
// We remove the observer from the memory
NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: "productsToLoad"), object: nil)
}
}
Screenshot:
Thank you for your time if you are reading this !
You need to remove this from viewWillDisappear of CartViewController
NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: "productsToLoad"), object: nil)
as when you post in products the cards are not shown so there is no listener inside it , beside that CartViewController should be opened at least once before you post any data from ProductsViewController
//
you can completely remove the NotificationCenter work , and do this in CartViewController
let products = ((self.tabBarController?.viewControllers![0] as! UINavigationController).topViewController as! ProductsViewController).selectedProductsArray
Note : Don't worry for ! unwrapping it won't crash
I have a view with a table on it, on every table cell I can add some data, so I put it in modal which actually is another view. In my modal I have this code
#IBAction func closeModal(_ sender: Any) {
if let amountVal = amount.text {
if let amountInt = Int16(amountVal) {
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let activity = Activity(context: context)
activity.created_at = Date() as NSDate
activity.amount = amountInt
countedObject?.addToActivities(activity)
do {
try context.save()
navigationController?.popViewController(animated: true)
} catch let error {
NSLog(error.localizedDescription)
}
}
}
dismiss(animated: true, completion: nil)
}
So I update core data entity and close modal, but after closing modal the first view was not updated so it does not reflect the changes I made until restart of the simulator. In my first view I have this
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func viewDidAppear(_ animated: Bool) {
populateCountObjects()
}
This works for simple segues but not for modal, what should I use in this case?
So I did it in another way, I added to ViewController this
static var sharedInstace : ViewController?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
ViewController.sharedInstace = self
}
and in the modal after dismiss method
ViewController.sharedInstace?.didCloseModal()
Posible duplicate : duplicate
You need to use a delegate with a dedicated method
protocol ModalDelegate {
func didCloseModal();
}
In your modal controller class, create an instance of ModalDelegate protocol. And call 'delegate.didCloseModal()' before dismiss
Then make your parent controller implement ModalDelegate protocol
and implement the function didCloseModal like viewDidAppear
Let the system do the work for you. In this case you get a notification when the context is saved.
override func viewDidLoad() {
super.viewDidLoad()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let center = NotificationCenter.default
center.addObserver(self, selector: #selector(contextDidSave(_:)), name: .NSManagedObjectContextDidSave, object: context)
}
func contextDidSave(_ notification: Notification) {
populateCountObjects()
}
If that doesn't work for you, you can always go lower and get notified whenever an object is changed.
override func viewDidLoad() {
super.viewDidLoad()
let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext
let center = NotificationCenter.default
center.addObserver(self, selector: #selector(contextObjectsDidChange(_:)), name: .NSManagedObjectContextObjectsDidChange, object: context)
}
func contextObjectsDidChange(_ notification: Notification) {
populateCountObjects()
}
I guess your viewDidAppear method isn't called again. Try to use NsNotification to notify your first VC if the context saved and redraw/refresh/reload...etc what you want.
I have already looked in Stackoverflow but I can't get an answer. I want to create function that stop playing the sound in another ViewController. But when I clicked the stop button, it cracked and showed "EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)". This is my code.
First ViewController
import UIKit
import AVFoundation
class FirstVC: UIViewController {
var metronome: AVAudioPlayer!
override func viewDidLoad() {
super.viewDidLoad()
do {
let resourcePath1 = Bundle.main.path(forResource: "music", ofType: "mp3")
let url = NSURL(fileURLWithPath: resourcePath1!)
try metronome = AVAudioPlayer(contentsOf: url as URL)
metronome.prepareToPlay()
metronome.play()
} catch let err as NSError {
print(err.debugDescription)
}
}
and another Viewcontroller is
import UIKit
class SecondVC: UIViewController {
var metronomePlay = FirstVC()
#IBAction func stopBtnPressed(_ sender: Any) {
metronomePlay.metronome.stop() //"EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)"
}
}
As of swift 4.1 today, this code worked for me:
Put this in sending controller:
NotificationCenter.default.post(name: Notification.Name(rawValue: "disconnectPaxiSockets"), object: nil)
Put this in receiving controller viewDidLoad() or viewWillAppear():
NotificationCenter.default.addObserver(self, selector: #selector(disconnectPaxiSocket(_:)), name: Notification.Name(rawValue: "disconnectPaxiSockets"), object: nil)
and then the following function in your receiving controller class:
#objc func disconnectPaxiSocket(_ notification: Notification) {
ridesTimer.invalidate()
shared.disconnectSockets(socket: self.socket)
}
Swift 5:
Put this in the Action
NotificationCenter.default.post(name: Notification.Name("NewFunctionName"), object: nil)
Put this in viewdidload() in a different viewcontroller (where is the function you want to use)
NotificationCenter.default.addObserver(self, selector: #selector(functionName), name: Notification.Name("NewFunctionName"), object: nil)
The function
#objc func functionName (notification: NSNotification){ //add stuff here}
I hope I was helpful
You are creating a NEW copy of FirstVC and calling stop on something that is not yet initialised.
You should really use a delegate in this case, something like
protocol controlsAudio {
func startAudio()
func stopAudio()
}
class FirstVC: UIViewController, controlsAudio {
func startAudio() {}
func stopAudio() {}
// later in the code when you present SecondVC
func displaySecondVC() {
let vc = SecondVC()
vc.delegate = self
self.present(vc, animated: true)
}
}
class SecondVC: UIViewController {
var delegate: controlsAudio?
// to start audio call self.delegate?.startAudio)
// to stop audio call self.delegate?.stopAudio)
}
So you are passing first VC to the second VC, so when you call these functions you are doing it on the actual FirstVC that is in use, rather than creating a new one.
You could do this without protocols if you like by replacing the var delegate: controlsAudio? with var firstVC: FirstVC? and assigning that, but I wouldn't recommend it
I use this way to call my functions from another viewControllers:
let sendValue = SecondViewController();
sendValue.YourFuncion(data: yourdata);
You can call function from other viewControllers in many ways.
Two ways that are already discussed above are by delegates & protocols and by sending notifications.
Another way is by passing closures to your second viewController from firstVC.
Below is the code in which while segueing to SecondVC we pass a closure to stop the metronome.
There will be no issue because you are passing the same firstVC (not creating a new instance), so the metronome will not be nil.
class FirstVC: UIViewController {
var metronome: AVAudioPlayer!
override func viewDidLoad() {
super.viewDidLoad()
do {
let resourcePath1 = Bundle.main.path(forResource: "music", ofType: "mp3")
let url = NSURL(fileURLWithPath: resourcePath1!)
try metronome = AVAudioPlayer(contentsOf: url as URL)
metronome.prepareToPlay()
metronome.play()
} catch let err as NSError {
print(err.debugDescription)
}
let secondVC = SecondVC()
secondVC.stopMetronome = { [weak self] in
self?.metronome.stop()
}
present(secondVC, animated: true)
}
}
class SecondVC: UIViewController {
var metronomePlay = FirstVC()
var stopMetronome: (() -> Void)? // stopMetronome closure
#IBAction func stopBtnPressed(_ sender: Any) {
if let stopMetronome = stopMetronome {
stopMetronome() // calling the closure
}
}
}
var metronomePlay = FirstVC()
you are creating a new instance on FirstVC, instead you should perform the function on the same instance that of already loaded FirstVC.
Updating #Scriptable's answer for Swift 4
Step 1 :
Add this code in your view controller, from which you want to press button click to stop sound.
#IBAction func btnStopSound(_ sender: AnyObject)
{
notificationCenter.post(name: Notification.Name("stopSoundNotification"), object: nil)
}
Step 2:
Now its final step. Now add this below code, to your result view controller, where you want to automatically stop sound.
func functionName (notification: NSNotification) {
metronomePlay.metronome.stop()
}
override func viewWillAppear(animated: Bool) {
NSNotificationCenter.defaultCenter().addObserver(self, selector: "functionName",name:"stopSoundNotification", object: nil)
}
You are initialising metronome in viewDidLoad method of FirstVC.
In SecondVC, you are initialising metronomePlay as a stored property, but never asking for ViewController's view and thus viewDidLoad of FirstVC is not getting called which results in metronome(stored property) not getting initialised.
You initialize metronome on FirstVC in viewDidLoad, which won't happen until you load the view of metronomePlay instantiated in SecondVC.
You have to call _ = metronomePlay.view, which will lazily load the view of SecondVC and subsequently execute viewDidLoad, before actually calling metronomePlay.metronome.
Try this in SecondVC. var metronomePlay = FirstVC().metronome
Either use the notification process to stop from anywhere or use same FirstVC instance from SecondVC class.
I have two View Controllers: "DiscoverViewController" and "LocationRequestModalViewController".
The first time a user opens the "DiscoverViewController", I overlay "LocationRequestModalViewController" which contains a little blurb about accessing the users location data and how it can help them.
On the "LocationRequestModalViewController" there are two buttons: "No thanks" and "Use location". I need to send the response from the user back to the "DiscoverViewController"
I have done some research and found that delegates/protocols are the best way to do it, so I followed a guide to get that working, but I'm left with 2 errors and can't figure them out.
The errors are:
On DiscoverViewController
'DiscoverViewController' is not convertible to 'LocationRequestModalViewController'
On LocationRequestModalViewController
'LocationRequestModalViewController' does not have a member name 'sendBackUserLocationDataChoice'
I've marked where the errors are happen in the following files:
DiscoverViewController.swift
class DiscoverViewController: UIViewController, UITextFieldDelegate, CLLocationManagerDelegate, LocationRequestModalViewControllerDelegate {
func showLocationRequestModal() {
var storyboard = UIStoryboard(name: "Main", bundle: nil)
var locationRequestVC: AnyObject! = storyboard.instantiateViewControllerWithIdentifier("locationRequestVC")
self.presentingViewController?.modalPresentationStyle = UIModalPresentationStyle.CurrentContext
self.tabBarController?.presentViewController(locationRequestVC as UIViewController, animated: true, completion: nil)
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
let vc = segue.destinationViewController as LocationRequestModalViewController
vc.delegate = self //This is where error 1 happens
}
func sendBackUserLocationDataChoice(controller: LocationRequestModalViewController, useData: Bool) {
var enableData = useData
controller.navigationController?.popViewControllerAnimated(true)
}
override func viewDidLoad() {
super.viewDidLoad()
showLocationRequestModal()
}
}
LocationRequestModalViewController
protocol LocationRequestModalViewControllerDelegate {
func sendBackUserLocationDataChoice(controller:LocationRequestModalViewController,useData:Bool)
}
class LocationRequestModalViewController: UIViewController {
var delegate:LocationRequestModalViewController? = nil
#IBAction func dontUseLocationData(sender: AnyObject) {
self.dismissViewControllerAnimated(true, completion: nil)
}
#IBAction func useLocationData(sender: AnyObject) {
delegate?.sendBackUserLocationDataChoice(self, useData: true) // This is where error #2 happens
}
override func viewDidLoad() {
super.viewDidLoad()
//Modal appearance stuff here...
}
}
The answer is in your question itself. Both errors tells the exact reason.
Issue 1
let vc = segue.destinationViewController as LocationRequestModalViewController
vc.delegate = self //This is where error 1 happens
The self is of type DiscoverViewController
But you declared the delegate as:
var delegate:LocationRequestModalViewController? = nil
You need to change that to:
var delegate:DiscoverViewController? = nil
Issue 2
The same reason, LocationRequestModalViewController does not confirm to the LocationRequestModalViewControllerDelegate, change the delegate declaration.
You have defined your delegate as having type LocationRequestModalViewController which does not conform to LocationRequestModalViewControllerDelegate.