Question 69426 in IOS Swift Question posted in
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How to pass data from First TabBarItem to Second TabBarItem – Ios swift

enter image description here

Above I have a TabBarController with 4 buttons. When I press the second TabBarItem(Cars) or third TabBarItem(Bicycles) I want to pass some values from the firstTabBarItem(HomeScreen) .
I’m using Swift 5 and I don’t have a SceneDelegate in my main project (is a 3 years old project), I have only the AppDelegate and this is why I wasn’t able to try the only example which I found from Stackoverflow about a similar question like mine.
I managed somehow to pass the data between ViewControllers through TabBarController but I don’t think is the right approach anymore (as some people from this community are also saying this on some threads) because when I click on different TabBarItems the data get lost and after is showing up again but with the wrong values etc.
I will attach below a GIF with the bugs which I’m getting while I navigate and also my current code with a link to the DEMO project on GitHub (https://github.com/florentin89/PassDataTabBarController/)

Can you help me please to pass the data using the right implementation ?

Here is my code for HomeScreen ViewController:

import UIKit

class HomeViewController: UIViewController {
    
    @IBOutlet var textfieldHoldingCarsValue: UITextField!
    @IBOutlet var textfieldHoldingBicyclesValue: UITextField!
    
    var valueForCarsScreen = String()
    var valueForBicyclesScreen = String()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        
        valueForCarsScreen = textfieldHoldingCarsValue.text ?? String()
        valueForBicyclesScreen = textfieldHoldingBicyclesValue.text ?? String()
        
        if let navController = self.tabBarController?.viewControllers?[1] as? UINavigationController{
            if let carsTab = navController.children.first as? PostcodeViewController{
                carsTab.receivedValueFromHomeScreen = valueForCarsScreen
            }
        }
        
        if let navController = self.tabBarController?.viewControllers?[2] as? UINavigationController{
            if let bicyclesTab = navController.children.first as? PostcodeViewController{
                bicyclesTab.receivedValueFromHomeScreen = valueForBicyclesScreen
            }
        }
    }
    
    // Logout the user and navigate to Login screen
    @IBAction func logoutTapped(_ sender: UIBarButtonItem) {
        self.view.window?.rootViewController?.dismiss(animated: true, completion: nil)
    }
}

Here is my code for the ViewController used for second and third TabBarItem:

import UIKit

class PostcodeViewController: UIViewController {
    
    @IBOutlet var receivedValueLabel: UILabel!
    
    var receivedValueFromHomeScreen = String()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
    }
    
    override func viewWillAppear(_ animated: Bool) {
        
        if self.tabBarController?.selectedIndex == 1 {
            receivedValueLabel.text = "Value received for Cars: n" + receivedValueFromHomeScreen
        }

        if self.tabBarController?.selectedIndex == 2 {
            receivedValueLabel.text = "Value received for Bicycles: n" + receivedValueFromHomeScreen
        }
    }
}

Here is a GIF with the bugs/glitches which I’m getting when I navigate between ViewControllers:

enter image description here

Thank you for reading this !

Tags:

3

Answers


  1. Chosen as BEST ANSWER
    0

    The fix was to move the code of PostcodeViewController from viewWillAppear to viewDidAppear like this:

        override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        print("Selected index: (self.tabBarController?.selectedIndex ?? -1)")
        
        if self.tabBarController?.selectedIndex == 1 {
            receivedValueLabel.text = "Value received for Cars: n" + receivedValueFromHomeScreen
        }

        if self.tabBarController?.selectedIndex == 2 {
            receivedValueLabel.text = "Value received for Bicycles: n" + receivedValueFromHomeScreen
        }
    }

    Now everything works perfect !

    GIF below:

    enter image description here


  2. 0

    a simple workaround can be.. store data in a static variable in login class, you can access it in other classes.

    long workaround is,

    create a Custom TabBar programmatically, pass data from login viewController to parent CustomTab bar, and pass data to next screen with the help of delegates.

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  3. 0

    The reason is that viewWillAppear of PostcodeViewController is called before the selectedIndex of your tabbar is changed. The first time it works ok. Just put the line:

    print("selected index = (self.tabBarController?.selectedIndex ?? -1)")

    in your viewWillAppear and you will see.

    The easiest way to fix your code is to move the logic of PostcodeViewController from viewWillAppear to viewDidAppear.

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