How to let Swift remember UIImage colours after seguing

Question

I'm just starting to learn Swift and I am building a simple application. The main page is simply a table:

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    let theData: [String] = ["BRDA", "HFH", "ENGRII", "HSSB", "GRVT"]
    let cellReuseIdentifier = "cell"

    @IBOutlet weak var tableView: UITableView!
    @IBAction func unwindToHome(segue: UIStoryboardSegue) { }

    override func viewDidLoad() {
        super.viewDidLoad()

        tableView.frame = CGRect(x: 0, y: 200, width: UIScreen.main.bounds.size.width, height: UIScreen.main.bounds.size.height-600)
        tableView.delegate = self
        tableView.dataSource = self
        tableView.register(UITableViewCell.self, forCellReuseIdentifier: cellReuseIdentifier)

        self.view.addSubview(tableView)
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return theData.count
    }

    internal func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell:UITableViewCell = tableView.dequeueReusableCell(withIdentifier: cellReuseIdentifier) as UITableViewCell!
        cell.textLabel?.text = theData[indexPath.row]
        return cell
    }

    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        if (indexPath.row == 0) {
            // segue to BRDA
            performSegue(withIdentifier: "toBRDA", sender: nil)
        } else {
            print("Will add later! You clicked on \(theData[indexPath.row]).")
        }
    }
}

I made the first entry clickable and I got it to segue to another controller. This new controller has an UIImage object and it simply changes colours when you tap on it.

class BRDAController: UIViewController {

    @IBOutlet weak var thePic: UIView!

    override func viewDidLoad() {
        super.viewDidLoad()
        var tapGesture = UITapGestureRecognizer()
        tapGesture = UITapGestureRecognizer(target: self, action: #selector(BRDAController.didTap(_:)))
        tapGesture.numberOfTapsRequired = 1
        tapGesture.numberOfTouchesRequired = 1
        thePic.addGestureRecognizer(tapGesture)
        thePic.isUserInteractionEnabled = true
        thePic.backgroundColor = UIColor.yellow
        // Do any additional setup after loading the view.
    }

    @objc func didTap(_ sender: UITapGestureRecognizer) {
        // User tapped at the point above. Do something with that if you want.
        if thePic.backgroundColor == UIColor.yellow {
            thePic.backgroundColor = UIColor.green
        } else {
            thePic.backgroundColor = UIColor.yellow
        }
    }

    @IBAction func backButton(_ sender: Any) {
        self.performSegue(withIdentifier: "goBackHome", sender: nil)
    }
}

I used an unwinding segue to go back to my home but when I go back to the other controller, the state has been reset (the colour has been set to its default yellow). How do I go about getting my code to 'remember' its previous state?

https://stackoverflow.com/questions/34366171/how-do-i-save-a-uicolor-with-userdefaults/34366333#34366333 — Leo Dabus, Mar 06 '19 at 06:47
Possible duplicate of [How do you pass data between view controllers in Swift?](https://stackoverflow.com/questions/25215476/how-do-you-pass-data-between-view-controllers-in-swift) — Prashant Tukadiya, Mar 06 '19 at 07:18

LinusGeffarth · Accepted Answer · 2019-03-06T09:56:21.937

4

It depends on the use case. If you want to save the data for...

...after quitting and relaunching the app, save it to user defaults
...the session only, when going back to the previous VC, use the delegate approach

Beyond the session: `UserDefaults`

@IBAction func backButton(_ sender: Any) {
    UserDefaults.standard.set(thePic.backgroundColor, forKey: "color")
}

...using the UserDefaults extension from here.

Next time you launch your app, read the color like this:

let color = UserDefaults.standard.color(forKey: "color")

Session-only: Delegate approach

Create a delegate protocol:

protocol BRDAControllerDelegate: class {
    func brdaController(_ brdaController: BRDAController, willDismissPassing data: [String: Any])
}

Then, create a delegate property:

class BRDAController: UIViewController {
    weak var delegate: BRDAControllerDelegate?

Just before dismissing, notify the delegate:

    @IBAction func backButton(_ sender: Any) {
        delegate?.brdaController(self, willDismissPassing: ["color": thePic.backgroundColor])
        // dismiss here
    }
}

Inside the presenting view controller, inherit from the delegate method:

class ViewController: ..., BRDAControllerDelegate {
    func brdaController(_ brdaController: BRDAController, willDismissPassing data: [String: Any]) {
        if let color = data["color"] as? UIColor {
            // do something with your color here
        }
    }

and set the delegate to self before transitioning:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    super.prepare(for: segue, sender: sender)
    if let brdaVC = segue.destination as? BRDAController {
        brdaVC.delegate = self
    }
}

Also, I suggest you to dismiss your view controller, instead of creating a new segue back:

@IBAction func backButton(_ sender: Any) {
    // embedded in navigation controller? use:
    navigationController?.popViewController(animated: true)
    // OR, no navigation controller? use:
    dismiss(animated: true)
}

edited Mar 06 '19 at 09:56

answered Mar 06 '19 at 06:40

LinusGeffarth

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However it is duplicate question but for your hard work to explain things and code Plus one :) – Prashant Tukadiya Mar 06 '19 at 07:42
1

Appreciate it! :) – LinusGeffarth Mar 06 '19 at 07:43
Thanks for the detailed answer! I'm still confused on what exactly I'm supposed to put in the `brdaController` func. Also, do you have recommended resources on dealing with delegates? – Ayumu Kasugano Mar 06 '19 at 08:03
You mean what to pass in the dict when passing the color to the delegate? – LinusGeffarth Mar 06 '19 at 08:04
Yes, I guess I'm failing to see how this exactly passes data to the `BRDAController`. – Ayumu Kasugano Mar 06 '19 at 08:06
Okay. You see, when you do `delegate = self` inside `ViewController`, you tell the `BRDAController` that self (`ViewController` in this case) wants to be notified upon changes. `weak var delegate: BRDAControllerDelegate` effectively *becomes* the `ViewController`. Since you then implement the callback method `willDismissPassing` inside `ViewController`, you can call this method from inside `BRDAController`. – LinusGeffarth Mar 06 '19 at 08:08
This also only works because `ViewController` isn't yet dismissed, but still open behind `BRDAController`. Otherwise the delegate would be nil. – LinusGeffarth Mar 06 '19 at 08:09
Ah I see! Thanks so much! – Ayumu Kasugano Mar 06 '19 at 08:16

How to let Swift remember UIImage colours after seguing

1 Answers1

Beyond the session: UserDefaults

Session-only: Delegate approach

Beyond the session: `UserDefaults`