Data transfer between tab view controllers - swift - ios

Question

There are 3 child tab view controllers. There are labels as 0 in view controllers. If the number(0) of labels increases in any view controller, I want to increase from the others. How can i do this data transfer.
class tab1Controller: UIViewController {
#IBOutlet weak var countLabel: UILabel!
var count = ""
override func viewDidLoad() {
super.viewDidLoad()
count = countLabel.text!
UserDefaults.standard.set(count, forKey: "count")
UserDefaults.standard.synchronize()
}
class tab2Controller: UIViewController {
#IBOutlet weak var countLabel2: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
countLabel2.text = UserDefaults.standard.string(forKey: "count")
}
I did something like this but it didn't work

Answer 1

I think the simplest way in your case is to update the label text in viewWillAppear method.
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
countLabel.text = UserDefaults.standard.string(forKey: "count")
}
You also should update the value in UserDefaults every time the number changes.

Answer 2

Do it i viewWillAppear() instead of viewDidLoad().. Because DidLoad() of all controllers called when tabBar construct and show first tab ...
#IBOutlet weak var countLabel2: UILabel!
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
countLabel.text = UserDefaults.standard.string(forKey: "count")
}

Answer 3

I assume that your child controllers are created at the same when the tab controller created. In such cases that needed to notify other existing controllers, you must use NotificationCenter.
A notification dispatch mechanism that enables the broadcast of information to registered observers.
extension Notification.Name {
static let didReceiveCountData = Notification.Name("didReceiveCountData")
}
class tab1Controller: UIViewController {
#IBOutlet weak var countLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Listen notifications for name .didReceiveCountData.
// onDidReceiveCountData(_:) will be called when notification received.
NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveCountData(_:)), name: .didReceiveCountData, object: nil)
}
// This will be called when the count changes.
#objc func onDidReceiveCountData(_ notification:Notification) {
if let newCount = notification.object as? String {
countLabel.text = newCount
}
}
// Call this when you need to change count and notify other tabs.
private func changeCount(_ newCount: String) {
NotificationCenter.default.post(name: .didReceiveCountData, object: newCount)
}
}
class tab2Controller: UIViewController {
#IBOutlet weak var countLabel: UILabel!
override func viewDidLoad() {
super.viewDidLoad()
// Listen notifications for name .didReceiveCountData.
// onDidReceiveCountData(_:) will be called when notification received.
NotificationCenter.default.addObserver(self, selector: #selector(onDidReceiveCountData(_:)), name: .didReceiveCountData, object: nil)
}
// This will be called when the count changes.
#objc func onDidReceiveCountData(_ notification:Notification) {
if let newCount = notification.object as? String {
countLabel.text = newCount
}
}
// Call this when you need to change count and notify other tabs.
private func changeCount(_ newCount: String) {
NotificationCenter.default.post(name: .didReceiveCountData, object: newCount)
}
}