如何在模态视图控制器被解除后更新父视图控制器的视图

Question

我有一个UIBarButtonItem，当它被解除时，我想从模态视图控制器的值进行更新。目前我只能通过获取我不想要的当前可见视图控制器来做到这一点。有没有办法在关闭模态视图后更新父视图控制器。

class HomeViewController: UIViewController {

    @IBOutlet weak var accountButton: UIBarButtonItem!

    override func viewWillAppear(_ pAnimated: Bool) {
        super.viewWillAppear(pAnimated)
        self.accountButton.title = User.current!.firstName
   }

@IBAction func accountButton(_ pSender: UIBarButtonItem) {
        let editUserAccountVC = UIStoryboard.fs_instantiateFromStoryboard("Main", identifier: "EditUserAccountViewController") as! EditUserAccountViewController
        let navVC = UINavigationController(rootViewController: editUserAccountVC)
        navVC.view.tintColor = self.view.tintColor
        self.present(navVC, animated: true)
       }
   }
}

这是编辑后关闭的模态

class EditUserAccountViewController: UIViewController {

    var firstName: String?

    @IBAction func saveButton(_ sender: Any) {
        self.dismiss(animated: true) {
            if let thePresentedViewController = self.presentingViewController as? HomeViewController {
                thePresentedViewController.accountButton.title = self.firstName
            }
        }    
    }
}

Answer 1

我认为您应该在模态控制器实例中存储对父控制器的引用。您可以使用协议使其更通用。声明如下protocol：

protocol AccountButtonProvider: AnyObject {
    var accountButtonTitle: String? { set get }
}

AnyObject 需要将AccountButtonProvider 的引用声明为weak。我猜你需要它来避免内存泄漏。

使HomeViewController符合AccountButtonProvider：

extension HomeViewController: AccountButtonProvider {
    var accountButtonTitle: String? {
        set {
            accountButton.title = newValue
        }
        get {
            return accountButton.title
        }
    }
}

然后将以下属性添加到EditUserAccountViewController：

weak var accountButtonProvider: AccountButtonProvider?

在呈现EditUserAccountViewController 之前初始化此属性。为此，请将editUserAccountVC.accountButtonProvider = self 添加到accountButton(_:)：

@IBAction func accountButton(_ pSender: UIBarButtonItem) {
    let editUserAccountVC = UIStoryboard.fs_instantiateFromStoryboard("Main", identifier: "EditUserAccountViewController") as! EditUserAccountViewController
    editUserAccountVC.accountButtonProvider = self
}

你也应该修改saveButton(_:):

@IBAction func saveButton(_ sender: Any) {
    self.dismiss(animated: true) {
        self.accountButtonProvider?.actionButtonTitle = self.firstName
    }
}

本文中的所有代码都在 Xcode 10.2.1 中进行了测试。我用的是 Swift 5。

Answer 2

您可以使用 closure 来解决您的问题陈述。

1.在EditUserAccountViewController中创建一个closure

var handler: ((String?)->())?

2.当EditUserAccountViewController从HomeViewController呈现时，设置这个closure的值

controller.handler = {(name) in
    self.accountButton.title = name
}

3. 在按下saveButton 时EditUserAccountViewController 被关闭时调用closure

self.dismiss(animated: true) {
    self.handler?(self.firstName)
}

编译后的代码：

class HomeViewController: UIViewController {
    @IBOutlet weak var accountButton: UIBarButtonItem!

    @IBAction func openEditUserAccountVC(_ sender: Any) {
        if let controller = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "EditUserAccountViewController") as? EditUserAccountViewController {
            controller.handler = {(name) in
                self.accountButton.title = name
            }
            self.present(controller, animated: true, completion: nil)
        }
    }
}

class EditUserAccountViewController: UIViewController {
    var firstName: String?
    var handler: ((String?)->())?

    @IBAction func saveButton(_ sender: Any) {
        self.dismiss(animated: true) {
            self.handler?(self.firstName)
        }
    }
}

Answer 3

只需使用委托设计模式。它简单易懂。