从一个视图控制器到另一个视图控制器进行委托调用

Question

我在 Swift 中没有做过的一件事是使用委托。所以我试图从一个视图控制器到另一个视图控制器进行委托调用以传递数据。

我有两个跨两个独立故事板的视图控制器。一个是 HomeViewController，第一个视图控制器。这就是用户现在所处的位置。然后他点击右侧导航项按钮转到第二个视图控制器 SettingsViewController。然后他点击导航项按钮返回到第一个视图控制器。在返回的路上，SettingsViewController 向 HomeViewController 发送了一个Int 值。我所拥有的是以下内容。

// 1st view controller //
class HomeViewController: UIViewController, SettingsViewControllerDelegate {
    @IBAction func rightTapped(sender: AnyObject) {
        let storyboard = UIStoryboard(name: "Settings", bundle: nil)
        let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
        let view = controller.topViewController as! SettingsViewController
        view.selectedRow = lineSelection
        self.navigationController?.pushViewController(view, animated: true)
    }

    override func viewDidLoad() {
        let storyboard = UIStoryboard(name: "Settings", bundle: nil)
        let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
        let settingsViewController = controller.topViewController as! SettingsViewController
        settingsViewController.delegate = self
    }

    func didChangeLine(number: Int) {
        print(number) // <<<<<<<<< not getting a delegate call
    }
}

// 2nd view controller //
protocol SettingsViewControllerDelegate {
    func didChangeLine(number: Int)
}

class SettingsViewController: UIViewController {
    var selectedRow = Int() // the row selected from a table view
    var rightButton = UIBarButtonItem()

    override func viewDidLoad() {
        rightButton = UIBarButtonItem(title: "Change", style: .Plain, target: self, action: #selector(changeNumber))
        self.navigationItem.rightBarButtonItem  = rightButton
    }

    // going back to 1st view controller (HomeViewController)
    func changeNumber() {
        self.delegate?.didChangeLine(selectedRow)
        self.navigationController?.popViewControllerAnimated(true)
    }
}

当用户从第二个（设置）返回到第一个视图控制器（主页）时，我没有接到电话。我可以用不同的方法传递数据，但我想知道我在这种情况下做错了什么。

谢谢。

Answer 1

在这个Protocol-Sample 中，我模拟了调用 HomeViewController 的 'didChangeLine' 函数的相同场景，如下图所示。

Answer 2

试试这个方法，这里我创建了一个变量 settingsViewController，我在 viewDidLoad() 方法中设置它，并在用户点击右键时使用它，而不是创建一个新的 settingsViewController。

// 1st view controller //
class HomeViewController: UIViewController, SettingsViewControllerDelegate {

    var settingsViewController: SettingsViewController? 
    // creating a variable so that we can use it in the IBOutlet 
    // method after setting it in the viewDidLoad() method

    @IBAction func rightTapped(sender: AnyObject) {
        settingsViewController.selectedRow = lineSelection
        self.navigationController?.pushViewController(settingsViewController, animated: true)
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let storyboard = UIStoryboard(name: "Settings", bundle: nil)
        let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
        settingsViewController = controller.topViewController as? SettingsViewController
        settingsViewController.delegate = self
    }

    func didChangeLine(number: Int) {
        print(number) 
    }
}

Answer 3

您需要在第一个 viewcontroller 中覆盖 prepareForSegue 以将第一个 viewcontroller ref 传递给 secondviewcontroller 委托属性。

override func prepareForSegue(segue: UIStoryboardSegue?, sender: AnyObject?) {
        let viewController = segue.destinationViewController as! SettingsViewController
        viewController.delegate = self
}

在HomeViewController viewDidLoad 中的代码没有任何意义，因为您正在从情节提要执行segue。

更新

@IBAction func rightTapped(sender: AnyObject) {
    let storyboard = UIStoryboard(name: "Settings", bundle: nil)
    let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
    let view = controller.topViewController as! SettingsViewController
    view.delegate = self

   view.selectedRow = lineSelection
    self.navigationController?.pushViewController(view, animated: true)
}

您可以直接获取 SettingViewController 参考。只需设置 viewcontroller 故事板 id 并像这样获取它

 let storyboard = UIStoryboard(name: "Settings", bundle: nil)
 let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController

let controller = storyboard.instantiateViewController(withIdentifier: "SettingsViewController") as! SettingsViewController

Answer 4

@IBAction func rightTapped(sender: AnyObject) {
        let storyboard = UIStoryboard(name: "Settings", bundle: nil)
        let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
        let view = controller.topViewController as! SettingsViewController
        view.selectedRow = lineSelection
        self.navigationController?.pushViewController(view, animated: true)
    }

改为：

@IBAction func rightTapped(sender: AnyObject) {
        let storyboard = UIStoryboard(name: "Settings", bundle: nil)
        let controller = storyboard.instantiateViewControllerWithIdentifier("InitialController") as! UINavigationController
        let view = controller.topViewController as! SettingsViewController
        view.selectedRow = lineSelection
view.delegate = self
        self.navigationController?.pushViewController(view, animated: true)
    }

Answer 5

在 SettingsViewController 类中更改以下方法：-

override func viewDidLoad() {
        rightButton = UIBarButtonItem(title: "Back", style: .Plain, target: self, action: #selector(changeNumber))
        self.navigationItem.leftBarButtonItem  = rightButton
    }