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 {
Related
I want to access NSCache from more than one place in my APP, as I'm using it to cache images from an API endpoint.
For example table view 4 and viewcontroller 6 in the diagram below use the same images, so I do not want to download them twice.
Candidate solutions:
Singleton
class Cache {
private static var sharedCache: NSCache<AnyObject, AnyObject>?
static public func getCache () -> NSCache<AnyObject, AnyObject> {
if sharedCache == nil {
self.sharedCache = NSCache()
}
return sharedCache!
}
}
Seems to work fine, but "Singletons are bad" so...
Store the cache in TabViewController
This will tightly couple the views to the view controller so...
Store in the AppDelegate somehow. But isn't this the same as 1? So...
Use dependency injection. But we're in a tab view controller, so isn't this the same as 2?
I'm not sure the right strategy here, so am asking whether there is another method that can be used here.
What I've done Created an App with an example using a NSCache, and explored a singleton solution. Ive tried to use dependency injection but think that it doesn't make sense. I've looked at Stack overflow and documentation, but for this specific circumstance I have found no potential solutoins.
What I've given A minimal example, with a diagram and tested solution that I'm dissatisfied with.
What is not helpful are answers that say NSCache is incorrect, or to use libraries. I'm trying to use NSCache for my own learning, this is not homework and I want to solve this specific instance of this problem in this App structure.
What the question is How to avoid using a singleton in this instance, view controllers in a tab view controller.
First up. Singletons are not inherantly bad. They can make your code hard to test and they do act as dependancy magnets.
Singletons are good for classes that are tools e.g NSFileManager aka FileManger, i.e something that does not carry state or data around.
A good alternative is dependancy injection but with view controllers and storyboards it can be hard and feel very boilerplate. You end up passing everything down the line in prepareForSegue.
One possible method is to declare a protocol that describes a cache like interface.
protocol CacheProtocol: class {
func doCacheThing()
}
class Cache: CacheProtocol {
func doCacheThing() {
//
}
}
Then declare a protocol that all things that wish to use this cache can use.
protocol CacheConsumer: class {
var cache: CacheProtocol? { get set }
func injectCache(to object: AnyObject)
}
extension CacheConsumer {
func injectCache(to object: AnyObject) {
if let consumer = object as? CacheConsumer {
consumer.cache = cache
}
}
}
Finally create a concrete instance of this cache at the top level.
/// Top most controller
class RootLevelViewController: UIViewController, CacheConsumer {
var cache: CacheProtocol? = Cache()
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
injectCache(to: segue.destination)
}
}
You could pass the cache down the line in prepareForSegue.
Or you can use subtle sub-classing to create conformance.
class MyTabBarController: UITabBarController, CacheConsumer {
var cache: CacheProtocol?
}
Or you can use delegate methods to get the cache object broadcast downhill.
extension RootLevelViewController: UITabBarControllerDelegate {
func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
injectCache(to: viewController)
}
}
You now have a system where any CacheConsumer can use the cache and pass it downhill to any other object.
If you use the coordinator pattern you can save the cache in the coordinator for your navigation flow and access it from there/init with the cache. It also works nicely since when the navigation flow is removed the cache is also removed.
final class SomeCoordinator: NSObject, Coordinator {
var rootViewController: UINavigationController
var myCache = NSCache<AnyObject, AnyObject>()
override init() {
self.rootViewController = UINavigationController()
super.init()
}
func start() {
let vc = VC1(cache: myCache)
vc.coordinator = self
rootViewController.setViewControllers([vc], animated: false)
parentCoordinator?.rootViewController.present(rootViewController, animated: true)
}
func goToVC2() {
let vc = VC2(cache: myCache)
vc.coordinator = self
rootViewController.pushViewController(vc, animated: true)
}
func goToVC3() {
let vc = VC3(cache: myCache)
vc.coordinator = self
rootViewController.present(vc, animated: true)
}
func goToVC4() {
let vc = VC4(cache: myCache)
vc.coordinator = self
rootViewController.present(vc, animated: true)
}
deinit {
print("✅ Deinit SomeCoordinator")
}
}
In my AppDelegate's applicationDidFinishLaunching I need to create an object using data read from disk, and then pass this object to the initial view controller for display. What would be the best way to do this?
Right now I'm loading the storyboard programatically like so:
func applicationDidFinishLaunching(_ aNotification: Notification) {
importantThing = ImportantThing()
importantThing.load(url: URL(fileURLWithPath: "..."))
let storyboard = NSStoryboard(name: "Main", bundle: nil)
myWindowController = storyboard.instantiateController(withIdentifier: "MyWindowController") as! NSWindowController
(myWindowController.contentViewController as? MyViewController)?.importantThing = importantThing
myWindowController.showWindow(self)
}
But this feels clunky. For one, the property is being set after viewDidLoad, so now view setup is weird.
There must be a better way to do this. If possible, I would like to not resort to using a singleton, because I actually need to set up a few interconnected objects (two objects with important state that have references to each other, but it doesn't make sense for either to contain the other). What would be a good way to solve this?
What you're doing in the app delegate is correct. As for what you should do in the view controller, Apple's Master-Detail app template shows you the correct pattern (I've added a few comments):
// the interface
#IBOutlet weak var detailDescriptionLabel: UILabel!
// the property
var detailItem: NSDate? {
didSet {
self.configureView()
}
}
func configureView() {
// check _both_ the property _and_ the interface
if let detail = self.detailItem { // property set?
if let label = self.detailDescriptionLabel { // interface exists?
label.text = detail.description
}
}
}
override func viewDidLoad() {
super.viewDidLoad()
// at this point, its _certain_ that the interface exists
self.configureView()
}
If you think about it, you'll see that the interface is updated correctly regardless of the order of events — that is, regardless of whether viewDidLoad or the setting of the property comes first. Just follow that pattern.
I'm trying to enable or disable an #IBOutlet UIButton Item of a toolbar from a UIView.
The button should get disabled when the array that I'm using in EraseView.Swift is empty.
I tried creating an instance of the view controller but it gives me the error (found nil while unwrapping):
in EraseView:
class EraseView: UIView {
...
let editViewController = EditImageViewController()
//array has item
editViewController.undoEraseButton.enabled = true //here I get the error
...
}
I tried to put a global Bool that changed the value using it in EditImageViewController but it doesn't work:
var enableUndoButton = false
class EditImageViewController: UIViewController {
#IBOutlet weak var undoEraseButton: UIBarButtonItem!
viewDidLoad() {
undoEraseButton.enabled = enableUndoButton
}
}
class EraseView: UIView {
...
//array has item
enableUndoButton = true //here I get the error
...
}
I know it's simple but I can't let it work. Here's the situation:
The root of the problem is the line that says:
let editViewController = EditImageViewController()
The EditImageViewController() says "ignore what the storyboard has already instantiated for me, but rather instantiate another view controller with no outlets hooked up and use that." Clearly, that's not what you want.
You need to provide some way for the EraseView to inform the existing view controller whether there was some change to its "is empty" state. And, ideally, you want to do this in a way that keeps these two classes loosely coupled. The EraseView should only be informing the view controller of the change of the "is empty" state, and the view controller should initiate the updating of the other subviews (i.e. the button). A view really shouldn't be updating another view's outlets.
There are two ways you might do that:
Closure:
You can give the EraseView a optional closure that it will call when it toggles from "empty" and "not empty":
var emptyStateChanged: ((Bool) -> ())?
Then it can call this when the state changes. E.g., when you delete the last item in the view, the EraseView can call that closure:
emptyStateChanged?(true)
Finally, for that to actually do anything, the view controller should supply the actual closure to enable and disable the button upon the state change:
override func viewDidLoad() {
super.viewDidLoad()
eraseView.emptyStateChanged = { [unowned self] isEmpty in
self.undoEraseButton.enabled = !isEmpty
}
}
Note, I used unowned to avoid strong reference cycle.
Delegate-protocol pattern:
So you might define a protocol to do that:
protocol EraseViewDelegate : class {
func eraseViewIsEmpty(empty: Bool)
}
Then give the EraseView a delegate property:
weak var delegate: EraseViewDelegate?
Note, that's weak to avoid strong reference cycles. (And that's also why I defined the protocol to be a class protocol, so that I could make it weak here.)
The EraseView would then call this delegate when the the view's "is empty" status changes. For example, when it becomes empty, it would inform its delegate accordingly:
delegate?.eraseViewIsEmpty(true)
Then, again, for this all to work, the view controller should (a) declare that is conforms to the protocol; (b) specify itself as the delegate of the EraseView; and (c) implement the eraseViewIsEmpty method, e.g.:
class EditImageViewController: UIViewController, EraseViewDelegate {
#IBOutlet weak var undoEraseButton: UIBarButtonItem!
override func viewDidLoad() {
super.viewDidLoad()
eraseView.delegate = self
}
func eraseViewIsEmpty(empty: Bool) {
undoEraseButton.enabled = !empty
}
}
Both of these patterns keep the two classes loosely coupled, but allow the EraseView to inform its view controller of some event. It also eliminates the need for any global.
There are other approaches that could solve this problem, too, (e.g. notifications, KVN, etc.) but hopefully this illustrates the basic idea. Views should inform their view controller of any key events, and the view controller should take care of the updating of the other views.
Recently I have been making a app where you can create and quiz yourself on definitions or anything for that matter. I pass data to the next view after it the user hits the create button to make the title of the new notecard. The code I am using right now for that is:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
let DestViewController: Card1 = segue.destinationViewController as! Card1
DestViewController.Content = Notetitle.text!
self.saved = self.Notetitle.text!
}
All of that works but, it will only work if I have a segue between viewcontrollers. I need to be able to pass that data with out a segue because I want the user to be able to create as many notecards as they want and the way I am trying to do that now is by using this code to make a copy of the UIView and then put in the new data (a master view). The new view can only be create using an IBAction. The prepare for segue I cannot use in the IBAction because it is it's own override function.
This is the code I am using to make a the new view:
let newCard =
self.storyboard!.instantiateViewControllerWithIdentifier("Main")
self.presentViewController(newCard, animated: true, completion:nil)
My hope is that I will be able to make a new view and then pass in the data pass in the data that the user just made to go on the notecard. (Hope this makes any sense at all)
MAIN TOPICS: -Create a new view and pass in new data Problem: Can pass data without a segue dont have one :/ -Be able to pass data between view controllers without a segue :)
I am new to all of this about 5 months. All of my code is in swift. Take it easy on me please. Feel free to ask me with any questions or comments. I have already posted a question on this but I didnt get an answer so have at it.
Thanks, Lucas Mazza
Don't use global variables unless you really need to. Making global static singleton's does not follow best practices. For more information read: What is so bad about singletons?
A better solution
You can use the protocol delegate pattern. I've actually written an article on this topic here:
https://www.codebeaulieu.com/36/Passing-data-with-the-protocol-delegate-pattern
You'll need a protocol that defines a function that will accept data. Then your other view controller will need to implement the delegate. If you need step-by-step details see the link provided above, alternatively you can simply download the project below and examine the code.
Download Working Example Project
Here's the code to make your protocol-delegate pattern work:
View Controller 1:
class ViewController: UIViewController, PresentedViewControllerDelegate {
#IBOutlet weak var textOutlet: UILabel!
#IBAction func doPresent(sender: AnyObject) {
let pvc = storyboard?.instantiateViewControllerWithIdentifier("PresentedViewController") as! PresentedViewController
pvc.data = "important data sent via delegate!"
pvc.delegate = self
self.presentViewController(pvc, animated: true, completion: nil)
}
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.
}
func acceptData(data: AnyObject!) {
self.textOutlet.text = "\(data!)"
}
}
View Controller 2:
import UIKit
// place the protocol in the view controller that is being presented
protocol PresentedViewControllerDelegate {
func acceptData(data: AnyObject!)
}
class PresentedViewController: UIViewController {
// create a variable that will recieve / send messages
// between the view controllers.
var delegate : PresentedViewControllerDelegate?
// another data outlet
var data : AnyObject?
#IBOutlet weak var textFieldOutlet: UITextField!
#IBAction func doDismiss(sender: AnyObject) {
if textFieldOutlet.text != "" {
self.presentingViewController!.dismissViewControllerAnimated(true, completion: nil)
}
}
override func viewDidLoad() {
super.viewDidLoad()
print("\(data!)")
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
override func viewWillDisappear(animated: Bool) {
super.viewWillDisappear(animated)
if self.isBeingDismissed() {
self.delegate?.acceptData(textFieldOutlet.text)
}
}
}
Sorry in advance that I can’t explain myself very well. I’m really new to programming and the topic of delegation still eludes me. I had some great help with this once before, but now I am trying to use a delegate in a different situation and I can’t get it right. I pieced together a bit of code that doesn’t work, and no matter how much I search I can’t find a way to fix it.
I have a view controller (MainController) with and embedded view controller (EmbeddedController) in a container view. I am trying to have a button in the embedded controller manipulate the container view (containerView).
EmbeddedController:
protocol ControllerDelegate {
func hideContainerView()
}
class EmbeddedController: UIViewController {
var delegate: VControllerDelegate?
#IBAction func button(sender: AnyObject) {
delegate?.hideContainerView()
}
}
MainController:
class MainController: UIViewController, ControllerDelegate {
#IBOutlet var containerView: UIView!
func hideContainerView() {
containerView.hidden = true
}
override func viewDidLoad() {
super.viewDidLoad()
var vc = EmbeddedController()
vc.delegate = self
}
}
Does anyone have any idea what I am doing wrong? And why this isn’t working?
What I ended up doing is adding this to the MainController:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if (segue.identifier == "mySegue") {
let vc = segue.destinationViewController as! EmbeddedController
vc.delegate = self
}
}
In storyboard I selected the segue from the MainController to the EmbeddedController, and set the identifier to "mySegue".
Without the code above the delegate kept returning nil. I didn't look into this solution at first as I thought segues were only for transitioning between view controllers, and in my mind I didn't see the embedded controller as a transition. Maybe someone more knowledgable than me (which is practically anyone on here at this point) can explain how this is all fitting together.
In any case, this is how I solved my issue and hopefully someone else can benefit from this as well :)
First of all, to avoid strong reference cycles:
protocol ControllerDelegate: class {
func hideContainerView()
}
class EmbeddedController: UIViewController {
weak var delegate: ControllerDelegate?
And you haven't added your newly instantiated VC view to container view, and not added it as a child VC:
let vc = EmbeddedController()
vc.delegate = self
containerView.addSubview(vc.view)
self.addChildViewController(vc)
vc.didMoveToParentViewController(self)