我需要执行一个动作(清空一个数组),当UINavigationController的后退按钮被按下,而按钮仍然导致堆栈上的前一个ViewController出现。我如何使用swift来实现这一点?


当前回答

你可以子类化UINavigationController并重写popViewController(animated: Bool)。除了能够在那里执行一些代码,你还可以防止用户完全返回,例如提示保存或丢弃他当前的工作。

示例实现,其中您可以设置popHandler,由推送的控制器设置/清除。

class NavigationController: UINavigationController
{
    var popHandler: (() -> Bool)?

    override func popViewController(animated: Bool) -> UIViewController?
    {
        guard self.popHandler?() != false else
        {
            return nil
        }
        self.popHandler = nil
        return super.popViewController(animated: animated)
    }
}

以及来自跟踪未保存工作的推送控制器的示例使用情况。

let hasUnsavedWork: Bool = // ...
(self.navigationController as! NavigationController).popHandler = hasUnsavedWork ?
    {
        // Prompt saving work here with an alert

        return false // Prevent pop until as user choses to save or discard

    } : nil // No unsaved work, we clear popHandler to let it pop normally

作为一个很好的触摸,这也将被interactivePopGestureRecognizer调用,当用户试图返回使用滑动手势。

其他回答

我通过调用/重写viewWillDisappear来实现这一点,然后像这样访问navigationController的堆栈:

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(animated)

    let stack = self.navigationController?.viewControllers.count

    if stack >= 2 {
        // for whatever reason, the last item on the stack is the TaskBuilderViewController (not self), so we only use -1 to access it
        if let lastitem = self.navigationController?.viewControllers[stack! - 1] as? theViewControllerYoureTryingToAccess {
            // hand over the data via public property or call a public method of theViewControllerYoureTryingToAccess, like
            lastitem.emptyArray()
            lastitem.value = 5
        }
    }
}

据我所知,你想清空你的数组,当你按下后退按钮,弹出到你之前的ViewController,让你的数组加载在这个屏幕上

let settingArray  = NSMutableArray()
@IBAction func Back(sender: AnyObject) {
    self. settingArray.removeAllObjects()
    self.dismissViewControllerAnimated(true, completion: nil)
} 
    override public func viewDidLoad() {
         super.viewDidLoad()
         self.navigationController?.navigationBar.topItem?.title = GlobalVariables.selectedMainIconName
         let image = UIImage(named: "back-btn")

         image = image?.imageWithRenderingMode(UIImageRenderingMode.AlwaysOriginal)

        self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: image, style: UIBarButtonItemStyle.Plain, target: self, action: #selector(Current[enter image description here][1]ViewController.back) )
    }

    func back() {
      self.navigationController?.popToViewController( self.navigationController!.viewControllers[ self.navigationController!.viewControllers.count - 2 ], animated: true)
    }

你可以简单地从堆栈中删除不必要的控制器,就像这样:

self.navigationController?.viewControllers.removeAll(where: {
        $0 is FirstViewController || $0 is SecondWithPinController
    })

这是我自己解决问题的方法

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    self.navigationItem.leftBarButtonItem?.action = #selector(self.back(sender:))
    self.navigationItem.leftBarButtonItem?.target = self
}

@objc func back(sender: UIBarButtonItem) {

}