Question

我想在两个ViewControllers之间传递数据抛出TabBarController。在第一个ViewController里面我找到了textField和button。在第二个我找到标签。当我在textField和push按钮中写一些文本时，我希望这个文本出现在第二个ViewController的Label中。但没有任何反应。

我的代码：

First ViewController：

import UIKit

class FirstViewController: UIViewController {
    @IBOutlet weak var textField: UITextField!

    @IBAction func enter(_ sender: Any) {
        if textField.text != "" {
            if let window = UIApplication.shared.delegate?.window, let tabBarController = window?.rootViewController as? UITabBarController, let second = tabBarController.viewControllers?.first as? SecondViewController {
                second.label.text = textField.text
                tabBarController.selectedIndex = 0
            }
        }
    }

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    }

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

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

第二个ViewController：

import UIKit

class SecondViewController: UIViewController {

    @IBOutlet weak var label: UILabel!
    var myString = String()

    override func viewDidLoad() {
        super.viewDidLoad()

        label.text = myString
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }


}

Answer 1

我认为问题在于

tabBarController.viewControllers?.first as? SecondViewController

你可能想要这样做：

tabBarController.viewControllers?[1] as? SecondViewController

不要忘记数组从0开始索引，因此viewControllers?[1]实际上返回数组中的第二个元素。

Answer 2

首先，我认为代表制表符的视图控制器应嵌入到导航控制器中，然后导航控制器将链接到TabBarController。

其次，在控制器之间发送数据的优先和推荐方法是通过协议（委托）。这是一个很好的例子，您可以一步一步地查看：https://medium.com/@jamesrochabrun/implementing-delegates-in-swift-step-by-step-d3211cbac3ef

但是，如果您正在寻找解决方案的快速解决方案，我认为Bruno Phillipe的答案在某种程度上得到了它，但并不完全。我们无法确定控制器在视图控制器列表中的哪个索引处。我认为这应该有效：

@IBAction func enter(_ sender: Any) {
    if textField.text != "" {
        if let window = UIApplication.shared.delegate?.window, let tabBarController = window?.rootViewController as? UITabBarController {

            //check if there are view controllers in the tabBarController
            guard let vcList = tabBarController.viewControllers else {

                return
            }

            for controller in vcList {

                if let second = controller as? SecondViewController {
                    //this will be executed only when a controller is SeconfViewController
                    second.label.text = textField.text
                    tabBarController.selectedIndex = 0
                }
            }

        }
    }
}

编辑：

我自己尝试了，问题是你试图设置label.text，实际上标签组件从未初始化。我想如果你只是将textField值存储到SecondViewController中的myString变量中，它就可以工作（不确定）。

然而，这是使用协议（委托）的解决方案，这是在控制器之间发送数据的正确方法。问你可能有任何问题。这应该有效：

FirstViewController：

import Foundation
import UIKit

protocol LabelChangeDelegate: class {

    func changeLabelWithText(_ text: String?)
}

class FirstViewController: UIViewController {

    weak var delegate: LabelChangeDelegate?

    @IBOutlet weak var textField: UITextField!

    @IBAction func enter(_ sender: UIButton) {

        if textField.text != "" {
            if let window = UIApplication.shared.delegate?.window, let tabBarController = window?.rootViewController as? UITabBarController {

                //check if there are view controllers in the tabBarController
                guard let vcList = tabBarController.viewControllers else {

                    return
                }

                for controller in vcList {

                    if let second = controller as? SecondViewController {
                        //this will be executed only when a controller is SeconfViewController

                        //set the delegate - who needs the data
                        delegate = second
                        //call the delegate function which will commmunicate with the delegate
                        delegate?.changeLabelWithText(textField.text!)
                        //don't know why you need this
                        tabBarController.selectedIndex = 0
                    }
                }

            }
        }
    }
    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    }

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

    override func didReceiveMemoryWarning() {
         super.didReceiveMemoryWarning()
         // Dispose of any resources that can be recreated.
    }


}

SecondViewController：

import Foundation
import UIKit

class SecondViewController: UIViewController, LabelChangeDelegate {

    @IBOutlet weak var label: UILabel!

    //lazy init
    lazy var myString = String()

    override func viewDidLoad() {
        super.viewDidLoad()

        //set label when the view loads, not in the first controller
        label.text = myString

        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
         super.didReceiveMemoryWarning()
         // Dispose of any resources that can be recreated.
    }

    //delegate function
    func changeLabelWithText(_ text: String?) {
        guard let sentText = text else {

            //no text sent
            return
        }

        myString = sentText
    }

}

Answer 3

我不建议你这样做。这是对理解的解释。

tabBarController中的viewControllers知道他们的tabBarController。您可以使用self.tabBarController。
secondViewController是viewControllers列表中的第二个let second = tabBarController.viewControllers?[1] as? SecondViewController。
如果您尚未访问secondViewController，则其视图将无法加载，因此网点仍为nil。您可以使用_ = second.view。
如果您想切换到第二个标签，则需要使用tabBarController.selectedIndex = 1。

@IBAction func enter(_ sender: Any) {
    if textField.text != "" {
        if let tabBarController = self.tabBarController as? UITabBarController, let second = tabBarController.viewControllers?[1] as? SecondViewController {
            // make sure view has loaded
            _ = second.view

            second.label.text = textField.text

            // change to second tab
            tabBarController.selectedIndex = 1
        }
    }
}

更好的方法......

您应该将字符串传递给SecondViewController的属性，而不是直接设置插座：

second.myString = textField.text ?? ""

然后在label的覆盖中将该字符串分配给viewWillAppear。

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    label.text = myString
}

在viewWillAppear中设置它的原因是viewWillAppear每次都会在显示视图之前运行。 viewDidLoad只会在首次加载视图时运行一次。由于您希望功能多次工作，viewWillAppear是正确的覆盖。

将数据传递给TabBar控制器

3 个答案: