I'm having some trouble understanding why the reloadData() line crashes with the following error 'unexpected found nil while unwrapping optional value'(also, why is it an optional?). Basically, when user taps a button it fires an API request, second VC(recipesVC) is shown and when data is retrieved from the API, in receivedRecipes method (previous VC) I want to reloadData from recipesVC (currentVC)
As my data is correctly passed to recipesVC, I don't see why reloadData() won't work on the same VC. Could you please give me a little help with this?
thank you.
override func viewDidLoad() {
super.viewDidLoad()
let recipes = Notification.Name(rawValue: "gotRecipes")
NotificationCenter.default.addObserver(self, selector: #selector(receivedRecipes),name: recipes, object: nil)
}
#objc func receivedRecipes() {
let recipesVC = storyboard?.instantiateViewController(withIdentifier: "recipesList") as! RecipesViewController
recipesVC.recipesList = request.recipeDetails
recipesVC.recipes.reloadData()
}
#objc func receivedRecipes() {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "recipes"), object: nil, userInfo: ["data":request.recipeDetails])
}
In your currentVC
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(receivedRecipes(notification:)),name: NSNotification.Name(rawValue: "recipes"), object: nil)
}
#objc func receivedRecipes(notification: Notification) {
recipesList = notification.userInfo
recipes.reloadData()
}
Add validation to your data:
func receivedRecipes() {
guard let details = request.recipeDetails else { return }
let recipesVC = storyboard?.instantiateViewController(withIdentifier: "recipesList") as! RecipesViewController
recipesVC.recipesList = details
recipesVC.recipes.reloadData()
}
The next tip, you can update your notification and get recipes from the notification.object, but previously you should paste them into:
let parsedRecipes = Recipes()
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "gotRecipes"), object: parsedRecipes, userInfo: nil)
Also show recipesVC after it initialization with:
self.present(...) or self.navigationController?.show(...)
Related
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)
}
}
I have this observer
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(GetUserID(_:)), name: Notification.Name("UserID"), object: nil)
}
and this selector function
#objc func GetUserID(_ notification: Notification){
let User = notification.object as? String
self.UserID = User
}
And I keep getting nil in UserID even though I am certain that when I get the notification it is not nil which makes me believe that the selector is not being called
You can get observer value by below method
let selectedIndex:[String: Int] = ["selectedIndex": 1]
//selectedindex = 0
// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "SelectedSegment"), object: nil, userInfo: selectedIndex)
NotificationCenter.default.addObserver(self, selector: #selector(self.changeSegmentControlIndex(notification:)), name: Notification.Name("SelectedSegment"), object: nil)
#objc func changeSegmentControlIndex(notification: Notification) {
if let selectedIndex = notification.userInfo?["selectedIndex"] as? Int {
// do something with your image
print(selectedIndex)
}
}
I have an pagMenuController on did select method I am passing the index. And in another vc I am getting that index values and I needs to show the view respective with incoming index value.
Code in my FirstVC:
func pageMenuController(_ pageMenuController: PageMenuController, didSelectMenuItem index: Int, direction: PageMenuNavigationDirection) {
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "updateView"), object: nil, userInfo: ["indexValue": index])
}
Code in my SecondVC:
override func viewWillAppear(_ animated: Bool) {
NotificationCenter.default.addObserver(self, selector: #selector(ContViewController.incomingNotification(_:)), name: NSNotification.Name(rawValue: "updateView"), object: nil)
}
#objc func incomingNotification(_ notification: Notification) {
if let indexVal = notification.userInfo?["indexValue"] as? Int {
print(indexVal)
}
}
When ever my screen appears, I needs to get the index values. But when I click on my menu items first, second time index values in not showing. 3rd, and above time its coming. what I have missed.
Any solutions?
Thank you
move your observer to viewdidload
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(ContViewController.incomingNotification(_:)), name: NSNotification.Name(rawValue: "updateView"), object: nil)
}
I've searched about this but the problem still exist for me. I found this great question but unfortunately it didn't work for me. This is the first time I'm working with NotificationCenter and the need to use this first occurs when I wanted to pass data to a viewcontroller under a tab of XLPagerTabStrip.
So here is how I am posting the Notification:
if let doc_ID = mainDoctorsArray[sender.tag].doctors_id {
NotificationCenter.default.post(name: Notification.Name("docID"), object: nil, userInfo: ["value" : doc_ID])
}
In the class I've made for observing this notification I'm calling NotificationCenter.default.addObserver(self, selector: #selector(gotDocID), name: Notification.Name("docID"), object: nil)
The selector method is:
func gotDocID(notification:NSNotification) {
let userInfo:Dictionary<String,String> = notification.userInfo as! Dictionary<String,String>
if let item = userInfo["value"] {
getDoctorDetails(docID: Int(item)!)
//print(item,self)
}
}
I've also tried adding observer as:
NotificationCenter.default.addObserver(self, selector: #selector(AvailableViewController.gotDocID(notification:)), name: Notification.Name("docID"), object: nil) but still same result.
The issue is that func gotDocID(notification:NSNotification) is not being called.
UPDATE
Class which is posting the notification is ViewController.swift and the class which has the observer is AvailableViewController.swift
Based on a comment I've changed observer to NotificationCenter.default.addObserver(self, selector: #selector(AvailableViewController.gotDocID(notification:)), name: Notification.Name("NotificationIdentifier"), object: nil) and this error is generated.
and also by doing the follow I'm getting the same error.
Value of type 'AvailableViewController' has no member 'gotDocID'
You can use the below code to post and get data.
//Post notification
NSNotificationCenter.defaultCenter().postNotificationName("docID", object: nil, userInfo: ["value" : doc_ID])
//Get data from observer
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(AvailableViewController.gotDocID(_:)), name: "docID", object: nil)
//Method called after notification is posted.
func gotDocID(notification: NSNotification) {
if let image = notification.userInfo?["value"] as? String {
// do something with your data
}
}
Please check :
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(self.gotDocID(notification:)), name: Notification.Name("docID"), object: nil)
}
#IBAction func saveButton(_ sender: UIButton) {
NotificationCenter.default.post(name: Notification.Name("docID"), object: nil, userInfo: ["value" : "123"])
}
#objc func gotDocID(notification:NSNotification) {
let userInfo:[String: String] = notification.userInfo as! [String: String]
if let item = userInfo["value"] {
print(item,self)
}
}
}
Add #objc to your function
#objc func gotDocID(notification:NSNotification) {
}
// Define identifier
let notificationName = Notification.Name("docID")
// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(AvailableViewController.gotDocID(notification:)), name: notificationName, object: nil)
// Post notification
NotificationCenter.default.post(name: notificationName, object: nil)
// Stop listening notification
NotificationCenter.default.removeObserver(self, name: notificationName, object: nil);
Why dont you try closure
Make sure your post notification occures.
Change
NotificationCenter.default.post(name: Notification.Name("docID") , object: ["value" : doc_ID])
NotificationCenter.default.addObserver(forName: Notification.Name("docID"), object: nil, queue: OperationQueue.main) { (notify) in
print(notify.object as! Dictionary<String,String>)
}
I am working on a test project in Swift 3. I am trying to pass textField string from one class to another class using NotificationCenter. I am trying to workout the answer from this link: pass NSString variable to other class with NSNotification and how to pass multiple values with a notification in swift
I tried few answers from the above link but nothing worked.
My code:
//First VC
import UIKit
extension Notification.Name {
public static let myNotificationKey = Notification.Name(rawValue: "myNotificationKey")
}
class ViewController: UIViewController {
#IBOutlet weak var textView: UITextView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func sendData(_ sender: AnyObject) {
let userInfo = [ "text" : textView.text ]
NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo)
}
}
//SecondVC
import Foundation
import UIKit
class viewTwo: UIViewController {
#IBOutlet weak var result: UILabel!
override func viewDidLoad() {
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(self.notificationReceived(_:)), name: .myNotificationKey, object: nil)
}
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
NotificationCenter.default.removeObserver(self, name: .myNotificationKey, object: nil)
}
func notificationReceived(_ notification: Notification) {
guard let text = notification.userInfo?["text"] as? String else { return }
print ("text: \(text)")
result.text = text
}
}
I am not sure whats wrong with the code. Above, code originally marked as a answered which, I found from the first link. Code been converted to Swift.
Don't use object parameter to pass data. It is meant to filter notifications with the same name, but from a particular object. So if you pass some object when you post a notification and another object when you addObserver, you won't receive it. If you pass nil, you basically turn off this filter.
You should use userInfo parameter instead.
First, it is better to define notification's name as extension for Notification.Name. This approach is much safer and more readable:
extension Notification.Name {
public static let myNotificationKey = Notification.Name(rawValue: "myNotificationKey")
}
Post notification:
let userInfo = [ "text" : text ]
NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo)
Subscribe:
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
NotificationCenter.default.addObserver(self, selector: #selector(self.notificationReceived(_:)), name: .myNotificationKey, object: nil)
}
Unsubscribe:
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
NotificationCenter.default.removeObserver(self, name: .myNotificationKey, object: nil)
}
Method to be called:
func notificationReceived(_ notification: Notification) {
guard let text = notification.userInfo?["text"] as? String else { return }
print ("text: \(text)")
}
Pass text using userInfo which is a optional Dictionary of type [AnyHashable:Any]? in Swift 3.0 and it is [NSObject : AnyObject]? in swift 2.0
#IBAction func sendData(_ sender: UIButton) {
// post a notification
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "notificationName"), object: nil, userInfo: ["text": textValue.text])
print(textValue) // textValue printing
}
in viewDidLoad
// Register to receive notification
NotificationCenter.default.addObserver(self, selector: #selector(self. incomingNotification(_:)), name: NSNotification.Name(rawValue: "notificationName"), object: nil)
and in incomingNotification
func incomingNotification(_ notification: Notification) {
if let text = notification.userInfo?["text"] as? String {
print(text)
// do something with your text
}
}
In your sendData method pass textField.text into Notification object and in your incomingNotification do this:
guard let theString = notification.object as? String else {
print("something went wrong")
return
}
resultLabel.text = theString
You can also use blocks to pass data between controllers.
Use dispatchQueue because your notification is posting before your view load. Therefore just give delay in your notification Post.
#IBAction func sendData(_ sender: AnyObject) {
let userInfo = [ "text" : textView.text ]
DispatchQueue.main.asyncAfter(deadline: .now() + 0.15) {
NotificationCenter.default.post(name: .myNotificationKey, object: nil, userInfo: userInfo) }
}
Just use NotificationCenter to send and receive the notification that state changed. Pass the data through some a data model such as an ObservableObject (particularly if you're bridging between SwiftUI and UIKit). Here's are a couple of extension that make it pretty simple for lightweight inter-component signaling without the cumbersome forgettable semantics of NotificationCenter. (Of course you define your own Notification.Name constants to be meaningful to your purpose).
extension Notification.Name {
static let startEditingTitle = Notification.Name("startEditingTitle")
static let stopEditingTitle = Notification.Name("stopEditingTitle")
}
extension NotificationCenter {
static func wait(_ name : Notification.Name) async {
for await _ in NotificationCenter.default.notifications(named: name) {
break;
}
}
static func post(_ name : Notification.Name) {
NotificationCenter.default.post(name: name, object: nil)
}
#discardableResult static func postProcessing(_ name: Notification.Name, using block: #escaping (Notification) -> Void) -> NSObjectProtocol {
NotificationCenter.default.addObserver(forName: name, object: nil, queue: OperationQueue.main, using: block)
}
}
To post a notification is as simple as:
NotificationCenter.post(.startEditingTitle)
And to receive the notification elsewhere:
NotificationCenter.postProcessing(.startEditingTitle) (_ in {
print("Started editing title")
}
Or to just wait for the notification instead of asynchronously handling it:
NotificationCenter.wait(.startEditingTitle)