CODEWITHSUNDEEP
iosswift
Alison.lwin
Alison.lwin

Reputation: 23

How would you save(append) data from one View Controller to another View Controller when you segue from a different view controller?

Sorry, the question is a bit long. Please bear with me.

Basically, I'm trying to write a simple count up/count down ios app using swift. I have three main view controllers. One is an "Initial View Controller" (which is the root view controller) that contain only two buttons - one that presents modally to the actual counting page (second view controller) and another present modally to a tableViewController page (third view controller). so those are the three view controllers.

So, if the user chooses to save the counter they have been counting I want to append the data on that counter view controller to an array I have created to be displayed on the tableViewController. So I'm making the tableViewController a delegate of the Counter View Controller to append the data to the array.

And as to my understanding, you need to implement prepareSegue in tableViewController to connect the tableViewController to the Counter View Controller. However, because the segue to the Counter View Controller doesn't originate from the tableViewController and instead from the Initial View Controller, the prepareSegue function is not working, and thus the delegate doesn't work. So to simplify my question- How would you save(append) data from one View Controller to another View Controller when you segue from a different view controller?

I hope my question was clear. I'm completely new to software development and not sure if I'm making any sense. Thanks so much for the help!

Upvotes: 2

Views: 362

Answers (2)

Nasir
Nasir

Reputation: 140

Solution 1 (Using Notifications):

Each time the counter is updated in CounterViewController, the following code needs to be executed:

let notification = Notification.init(name: NSNotification.Name(rawValue: "UpdateCounter"), object: NSNumber.init(value: 1), userInfo: nil)    

NotificationCenter.default.post(notification)

This code is implemented in the Initial View Controller (to observe for the changes in counter): 

override func viewDidLoad() {
   super.viewDidLoad()
   NotificationCenter.default.addObserver(self, selector: #selector(parseNotification(_:)), name: NSNotification.Name.init(rawValue: "UpdateCounter"), object: nil)
}

func parseNotification(_ notification: Notification?) {
    if let number = notification?.object as? NSNumber {
        /** here counter is a class variable in Initial ViewController **/
        counter = number.intValue
    }
}

And add the following code in prepareforSegue in the Initial View Controller

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    //Condition to check if TableViewController is being opened
    tableViewController.counter = counter
}

Don't forget to remove the observer in the Initial View Controller:

deinit {
    NotificationCenter.default.removeObserver(self)
}

Solution 2 (Using Global/Shared variables): Create a global/shared variable such as

class Shared {
    var value = 0
    let instance = Shared()
}

In the CounterViewController, you set the value every time the counter is updated

Shared.instance.value = counterValue

You can read the value in TableViewController using the following code:

Shared.instance.value

Upvotes: 0

Nima Yousefi
Nima Yousefi

Reputation: 817

If you have three controllers in the storyboard path, One -> Two -> Three, and you want One to know about data changes in Three, then you need to propagate the changes via Two.

A rough version might look like this:

protocol CountDelegate: class {
    func updateCount()
}

class One: UIViewController, CountDelegate {
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        guard let destination = segue.destination as? Two else { return }
        destination.delegate = self
    }

    func updateCount() {
        // whatever
    }

}

class Two: UIViewController {
    weak var delegate: CountDelegate?
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        guard let destination = segue.destination as? Three else { return }
        destination.delegate = self.delegate // just pass the delegate down
    }
}

class Three: UIViewController {
    weak var delegate: CountDelegate?

    func doWork() {
        self.delegate?.updateCount()
    }
}

So the delegate is One, and both Two and Three (via Two) point back to it as the delegate.

Upvotes: 1

Related Questions