How to send data back to previous screen IOS/Swift [duplicate] - ios

Question

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Passing data between view controllers
(45 answers)
Closed 2 years ago.
I am creating a library in IOS/swift that:
takes a user to a scene --> performs a task --> return to the initial scene that called the first while passing a payload back to the user
I have figured out how to take users back to the previous scene that called it, but my issue is how to send a payload back with it using thee code snippet below:
func switchToPreviousPage(){
self.dismiss(animated: true, completion: nil)
}
How do I achieve this?

Answer 1

In your scenario you can use either :
Delegation Pattern
Notification/Observer
Lets discuss each one :
1. Delegation :
If you have idea about Protocol in Swift you can do it easily.
first create a protocol with the required function you want to implement :
protocol FirstControllerDelegate: AnyObject {
func sendData(data: String)
}
Suppose your firstPage is FirstViewController, it has a UILabel and we have to assign a String to it from our secondPage means SecondViewController. the Structure of your FirstViewController may be like this :
class FirstViewController: UIViewController {
#IBOutlet weak var textLabel: UILabel!
#IBAction func gotoSecondPage() {
let secondVC = storyboard?.instantiateViewController(withIdentifier: "SecondViewController") as! SecondViewController
}
}
Now your FirstViewController has to confirm to this protocol and it will implement the sendData(data: ) method :
extension FirstViewController: FirstControllerDelegate {
func sendData(data: String) {
textLabel.text = data
}
}
Now as a feature of Protocol in iOS, Protocols can work as a Type(like Int, String). So just create a variable of type FirstControllerDelegate in your SecondViewController !
class SecondViewController: UIViewController {
weak var delegate: FirstControllerDelegate!
#IBAction func switchToPreviousPage() {
delegate.sendData(data: "Hello")
self.dismiss(animated: true, completion: nil)
}
}
You can now call the sendData(data:) function with the variable you created above !
At last you have to do oneThing just assign the delegate :
secondVC.delegate = self
It should be inside the gotoSecondPage() method !
2. Notification/Observer
With this, our basic idea is to send a Notification inside our app, and it can be observed by any where inside !
So our SecondViewController will send a Notification embedded with required data that we want to pass, and FirstViewController will receive the Notification and it will extract the data from the Notification !!
Each Notification has a specific name, which will differentiate it from other Notifications. we have to create the Name :
Notification.Name(rawValue: "com.app.notificationObserver")
Now the FirstViewController will be Observe to this specific notification :
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(self.changeLabelText(notifcation:)), name: Notification.Name("com.app.notificationObserver"), object: nil)
}
We have to define changeLabelText(notification:) method :
private func changeLabelTExt(notification: NSNotification) {
if let dataDict = notification.userInfo as NSDictionary? {
if let message = dataDict["data"] as? String {
self.textLabel.text = message
}
}
}
Finally, SecondViewController will trigger the Notification :
#IBAction func switchToPreviousPage() {
NotificationCenter.default.post(name: Notification.Name(rawValue: "com.app.notificationObserver"), object: ["data": "hello"])
self.dismiss(animated: true, completion: nil)
}
Thats All .....