I can't get the app to execute changeCard() after abc() finishes executing. The two functions are in different classes. Here is the code below. Any help is appreciated!
protocol NetworkControllerDelegate {
func changeCard()
}
class NetworkController {
var networkControllerDelegate: NetworkControllerDelegate?
func abc () {
//do something here
networkControllerDelegate?.changeCard()
}
}
class View: UIViewController, NetworkControllerDelegate {
var networkController = NetworkController()
func changeCard() {
//do something here
networkController.networkControllerDelegate = self
}
}
I've read all the similar questions on stackoverflow for the past few hours but still can't figure it out. Thanks!
Try moving the following line into viewDidLoad of your view controller so that the delegate is set up prior to use.
networkController.networkControllerDelegate = self
Also, you might want to think about making the networkControllerDelegate variable in NetworkController weak so as to avoid any retain cycles.
Related
might be a silly question, but I'm trying to understand better why I can't do this. I recall this working in Swift 5.6.1, but I recently updated to Swift 5.7.2.
Before asking, I want to note that I did see this question: Swift passing self as argument in class init, but it didn't quite answer my question. Or maybe I just want to see if these are the only solutions...
I have a couple of classes that's something like this.
class Bar {
weak var delegate: FooDelegate?
init(delegate: FooDelegate) {
self.delegate = delegate
}
}
class Foo: FooDelegate {
var bar: Bar
init() {
self.bar = Bar(delegate: self)
}
}
Before I updated, I don't remember this throwing any errors. Now I'm getting the error
Variable 'self.bar' used before being initialized.
Is there a way to set this up so that I'm passing the delegate correctly?
Thanks all!
You can solve this by breaking it up in two steps, create the Bar object and then set delegate
init() {
bar = Bar()
bar.delegate = self
}
Of course this requires a new init for the Bar class
Heres a caption of my API call:
So, I've got the abilities of the pokemons I needed, but now, idk how to get that data out of my Service class (where I'm doing all the parsing), and send it to my InfoViewController.
My purpose is to fetch that data on some label, and then show the ability names for every poke, according to their ID. Here is a caption of my app:
I wanna add an "Ability" label below Weight, and that's where I wanna assign the data. I have a whole CollectionView with all the pokemons, and the goal is assign the correct ability for each one of them.
I'm kinda struggling for a practical (and less verbose) way to reach this.
I apreciated every comment, any advice and suggestion too. Thanks!
EDIT: Heres my code:
extension InfoController: ServiceDelegate {
func finishedWithPokemonAbilities(abilities: [String], id: Int) {
self.abilities = abilities
self.ids = id
print(abilities)
}
}
You can create a custom Protocol(could call it PokemonServiceDelegate as an example) that your InfoViewController would inherit and implement. On your service object(I'm using PokemonService in the example) create a property with a type of PokemonServiceDelegate and set that property to the view controller that you want to receive the data. After the service finishes fetching the data, update the delegate by passing the data in the function declared in the protocol.
// Protocol your view controller will inherit
protocol PokemonServiceDelegate {
// Function your view controller will implement
func finishedWithPokemonAbilities(abilities: [String])
}
class InfoViewController: UIViewController {
// Reference to the service that makes the request
var service: PokemonService
override func viewDidLoad() {
...
// Set the delegate of the service to self
service.delegate = self
...
}
}
extension InfoViewController: PokemonServiceDelegate {
// Implement the protocol
func finishedWithPokemonAbilities(abilities: [String]) {
// Do something with their abilities here
}
}
struct PokemonService {
var delegate: PokemonServiceDelegate?
// The function that you call to get your abilities
func someUpdateFunc() {
...
let abilities = json[abilities].arrayValue.map {$0["ability"]["name"].stringValue}
delegate?.finishedWithPokemonAbilities(abilities: abilities)
...
}
}
I have issues with using protocols to send data back to previous controller. I have studied SO questions and guides, but for some reason my data doesn't get transferred back.
In my second class I create data, that is later being sent back to first class:
protocol ImageEditorDelegate {
func sendImage(image: UIImage, id: String)
}
class PhotoEditorViewController: UIViewController {
var delegate: ImageEditorDelegate?
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func didPressSave(_ sender: UIButton) {
delegate?.sendImage(image: finalImage, id: imageThatWasSelected)
self.dismiss(animated: true, completion: nil)
}
}
And in my receiving class I have:
class NewProductViewController: UIViewController, ImageEditorDelegate {
var imageEditor: PhotoEditorViewController?
override func viewDidLoad() {
super.viewDidLoad()
imageEditor?.delegate = self
}
func sendImage(image: UIImage, id: String) {
print("Receiving images", image, id)
switch id {
case "1":
selectedImages[1] = image
productImage1.image = image
case "2":
selectedImages[2] = image
productImage2.image = image
case "3":
selectedImages[3] = image
productImage3.image = image
default:
break
}
}
}
But nothing happens, this func never gets called. I think my delegate is nil, or so, but how could I fix this issue? I have Also, I'm using VIPER as architecture with slightly customized segues, may this be the issue? I have tried simple segues, but had same issue.
I understand that this is rather simple question, but I couldn't understand what I doing wrong after I have read articles about protocols.
Thanks for your help!
What you're doing is very wrong. You have two view controllers with property references to one another:
class PhotoEditorViewController: UIViewController {
var delegate: ImageEditorDelegate?
}
class NewProductViewController: UIViewController, ImageEditorDelegate {
var imageEditor: PhotoEditorViewController?
}
Those are not weak references, so if you ever do get this to work — that is, if you ever arrange things so that the NewProductViewController's imageEditor is a PhotoEditorViewController whose delegate is that NewProductViewController — you will have a nasty retain cycle and a memory leak.
This suggests that you have not understood the protocol-and-delegate pattern. Only the presented view controller should have a delegate property pointing back to the presenter, and it should be weak. The presenter does not need any property pointing to the presented view controller, because it presents it.
you need to instantiate your photoEditor, like
photoEditor = PhotoEditorViewController()
before attempting to set its delegate.
you dont' have to do this next part, but I'd suggest making the delegate variable a weak variable to avoid any retain issues, like so
weak var delegate: ImageEditorDelegate?
and you'll need to mark the protocol as class like so
protocol ImageEditorDelegate : class {
Passing data to the next viewController is simple and straightforward, and can be done using prepareSegue method. However, I can't understand how to pass data to a previous viewController in Swift(Cocoa Application)
I have a textfield in viewControllerB and when you type something in it and press a button, I want to pass it to a label in viewControllerA and instead of opening the viewControllerA in a new window, I just want the viewController B to be dismissed and the passed data to be visible on the viewControllerA.
That's all there is to it. I have been stuck on it for the past 48 hours. Any help on this will be appreciated.
Thanks!
You do this using delegates. Example:
protocol NextProtocol: class {
func sendBack(value: Int)
}
class Previous: NextProtocol {
func sendBack(value: Int) {
print("I have received \(value)")
}
func prepareSegue(...) {
// get next instance
var next: Next
next.delegate = self
}
}
class Next {
weak var delegate: NextProtocol?
func someMethod() {
delegate?.sendBack(5)
}
}
My program consists of three relatively-distinct areas: listening on a network for new state, performing network actions, and updating the UI. So respectively I want three classes: StateListener, ActionSender, and ViewController, each chugging along on separate threads.
Would that it were so simple -- the three need to interact. Some states discovered by the StateListener require Actions to be sent by the ActionSender or the UI to be updated by the ViewController. Some responses to Actions require the UI to be updated by the ViewController. Some UI actions require Actions to be performed by the ActionSender.
Currently I do something like this (pseudocode):
/* ViewController.swift */
class ViewController : blah
{
//...
func buttonPressed()
{
// ?! Need to do an action here but I can't
// because actionSender is initialised below...
}
func viewDidLoad()
{
let actionSender = ActionSender(m_view: self)
let actionQueue = OperationQueue()
let stateListener = StateListener(m_view: self,
m_actionSender: actionSender,
m_actionQueue: actionQueue)
let stateQueue = OperationQueue()
stateQueue.addOperation(stateQueue.listen())
}
}
/* StateListener.swift */
class StateListener
{
// ...
func listen()
{
while true
{
var state = waitForNewState()
if shouldActOn(state)
{
m_actionQueue.addOperation(m_actionSender.act())
}
}
}
}
/* ActionSender.swift */
class ActionSender
{
// ...
func act()
{
var reply = sendAction()
OperationQueue.main.addOperation(m_view.m_textBox.append(reply))
}
}
This is fairly hellish and doesn't even do what I want it to do, because I can't have the ViewController perform actions (ActionSender's require a ViewController reference to update the view after the action, but I tried initialising the ActionSender within ViewController.init and I got bizarre errors to do with a Code.init that I hadn't implemented...). I want to get above ViewController and initialise all these OperationQueues and objects wherever ViewController gets initialised, but I can't find where that is...
What I've done above is basically object-reference injection of each object and OperationQueue. I know there are other ways of doing this (a hierarchy of callbacks, NSNotifications) but I'm unsure of which is best.
My question is in two parts:
What is the best (i.e., fastest, easiest to implement and maintain, most idiomatic in Swift) way to get the inter-object and inter-thread communication I desire?
I currently get things going from ViewController's viewDidLoad function, which seems awful (and means I can't get a 'higher-up' perspective of the ViewController. Where should this stuff go? AppDelegate advertises itself as the 'program startup' area, but I can't access the ViewController from there... XCode seems to have hidden the startup of my app from me!
I really appreciate your responses!
This post greatly helped with question 2 and the problem of passing self as a parameter to a data member in an initialiser : http://blog.scottlogic.com/2014/11/20/swift-initialisation.html
Specifically, I can use this pattern:
class Foo : blah
{
var m_bar : Bar!
init() {
// notice I get away with not initialising m_bar
}
func viewDidLoad {
m_bar = Bar(m_foo: self)
m_bar.doYourThing()
}
}
The blog prefers the following, which I feel I should add here out of gratitude to the author, though I prefer the above.
class Foo : blah
{
lazy var m_bar : Bar = {
return Bar(m_foo: self) // notice I can pass in self
}
init() {
// notice I get away with not initialising m_bar
}
func viewDidLoad {
m_bar.doYourThing()
}
}