ios - Access the instance of a Viewcontroller from another in swift

Question

I am trying to transfer data from the textfield of one View Controller to the label from another.

How can I call the View Controller instance from the code of the other View Controller? I'm working with storyboards thus I never created an instance of the View Controllers in the code? Are the instances automatically created? And what name do they have?

Thanks for your help!

Answer 1

1. If the view controller containing the textfield can call (with a segue) the view controller containing the label...

Add a new Cocoa Touch class file in your project, name it FirstViewController and set the following code in it:

import UIKit

class FirstViewController: UIViewController {
    
    @IBOutlet weak var textField: UITextField! // FIXME: link this to the UITextField in the Storyboard!!!
    
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        let controller = segue.destinationViewController as! SecondViewController
        controller.text = textField.text
    }
    
}

Add a new Cocoa Touch class file in your project, name it SecondViewController and set the following code in it:

import UIKit

class SecondViewController: UIViewController {
    
    var text: String?
    @IBOutlet weak var label: UILabel! // FIXME: link this to the UILabel in the Storyboard!!!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        label.text = text
    }
    
}

In the Storyboard, embed the first view controller in a UINavigationController. Link the first view controller to the second with a UIButton or a UIBarButtonItem. Set the name of the first view controller to FirstViewController and the name of the second view controller to SecondViewController. Create a UITextField in the first view controller. Create a UILabel in the second view controller. Link the textfield and the label to their respective declarations in FirstViewController and SecondViewController.

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2. If the view controller containing the label can call (with a segue) the view controller containing the textfield...

Here, this is a perfect protocol/delegate case. You may find a lot of stuff on StackOverflow dealing with this. However, here is a rough example.

Add a new Cocoa Touch class file in your project, name it FirstViewController and set the following code in it:

import UIKit

class FirstViewController: UIViewController, DetailsDelegate {
    
    @IBOutlet weak var label: UILabel! // FIXME: link this to the UILabel in the Storyboard
    
    func updateLabel(withString string: String?) {
        label.text = string
    }
    
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        let controller = segue.destinationViewController as! SecondViewController
        controller.delegate = self
    }
    
}

Add a new Cocoa/Cocoa Touch class file in your project, name it SecondViewController and set the following code in it:

import UIKit

protocol DetailsDelegate: class {
    func updateLabel(withString string: String?)
}

class SecondViewController: UIViewController {
    
    weak var delegate: DetailsDelegate?
    @IBOutlet weak var textField: UITextField! // FIXME: link this to the UITextField in the Storyboard
    
    override func viewWillDisappear(animated: Bool) {
        super.viewWillDisappear(animated)
        
        delegate?.updateLabel(withString: textField.text)
    }

}

In the Storyboard, embed the first view controller in a UINavigationController. Link the first view controller to the second with a UIButton or a UIBarButtonItem. Set the name of the first view controller to FirstViewController and the name of the second view controller to SecondViewController. Create a UILabel in the first view controller. Create a UITextField in the second view controller. Link the textfield and the label to their respective declarations in FirstViewController and SecondViewController.