如何在标签栏iOS中将数据从ViewController传递到ViewController？

Question

I'm trying to pass data from my main ViewController to another ViewController in a Tab Bar.

I have tried using the following code , and got an error Could not cast value of type 'Test.FirstViewController' to 'Test.ViewController'

override func viewWillAppear(_ animated: Bool)
{
    super.viewWillAppear(animated)
    let tab1Controller = self.tabBarController?.viewControllers?.first as! ViewController
    print(tab1Controller.test)
}

Answer 1

I just used the following code which just worked fine for me on Xcode 9 with swift 4.0. The following method is declared in the View Controller class which just presents the First View Controller.

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "sendingToTabBar" {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let tabVC = storyboard.instantiateViewController(withIdentifier: "tabVC") as! UITabBarController
        self.present(tabVC, animated: true, completion: {
            let vc = tabVC.selectedViewController as! FirstViewController
            vc.dataLBL.text = self.dataTF.text!
        })
    }
}

Answer 2

You can access the tab bar controllers in your ViewController prepare method and set your values.

Prepare for segue

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    let barViewControllers = segue.destination as! UITabBarController
    let destinationViewController = barViewControllers.viewControllers?[0] as! FirstViewController
    destinationViewController.test = "Hello TabBar 1"

    // access the second tab bar
    let secondDes = barViewControllers.viewControllers?[1] as! SecondViewController
    secondDes.test = "Hello TabBar 2"
}

Then in your tab bar ViewControllers declare variables, you want to set the values to.

@IBOutlet weak var label: UILabel!
var test: String?

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    label.text = test
}

FirstViewController

SecondViewController

Answer 3

You could do a number of things, what I would do is to just make a global variable so that both view controllers can access it. Another option is to give each view controller a separate global variable, and when the view is loaded, the variable is set to self, then make a variable that can be set by the other view controller.

example:

var data:Any?
viewDidLoad() {
    viewControllerA = self
}