iOS - How to set imageview of a parent view controller through child container? - swift

Question

I am currently using a container view and I want to change the value of parent view controller imageView through child view controller using delegates, but it always returns nil.
import UIKit
protocol updateImage {
func userIsDone(image:UIImage)
}
class ViewController: UIViewController, updateImage{
#IBOutlet weak var imageView:UIImageView!
var image = UIImage(named: "hello.png")
override func viewDidLoad() {
super.viewDidLoad()
self.imageView.image=self.image
}
func userIsDone(image: UIImage) {
self.image=image
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if segue.identifier == "containerChild"{
let nextView = segue.destinationViewController as! ControllerChild
nextView.image=self.image
nextView.delegate=self
}
}
}
class ControllerChild:UIViewController{
var image=UIImage(named: "newhello.png")
var delegate: updateImage? = nil
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func changeImage(sender:UIButton){
if(delegate != nil){
self.delegate!.userIsDone(self.image!)
print("I am Called!")
}
}
}

Answer 1

Remove this line:
nextView.image = image
And change the userIsDone function to:
func userIsDone(image: UIImage) {
imageView.image = image
}
As side notes:
In Swift you don't need to use self outside of blocks/closures. For example, you don't need to self.imageView.image = self.image -- just imageView.image = image will do.
Protocols should be upper-cased, like UpdateImage (instead of updateImage).
You don't need that extra .png to reference images, just the title, E.g.: "hello".
Apple describes Swift code conventions in their awesome Swift book.
Here is the code, refactored (Swift 3):
import UIKit
protocol UpdateImageProtocol {
func userIsDone(image: UIImage)
}
class ViewController: UIViewController, UpdateImageProtocol {
#IBOutlet weak var imageView: UIImageView!
var image = UIImage(named: "hello")
override func viewDidLoad() {
super.viewDidLoad()
userIsDone(image: image!)
}
func userIsDone(image: UIImage) {
imageView.image = image
}
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "containerChild" {
let nextView = segue.destination as! ChildViewController
nextView.delegate = self
}
}
}
class ChildViewController: UIViewController {
var image = UIImage(named: "newHello")
var delegate: UpdateImageProtocol?
#IBAction func changeImage(sender: UIButton) {
delegate?.userIsDone(image: image!)
}
}