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
斯威夫特3:
override func didMove(toParentViewController parent: UIViewController?) {
super.didMove(toParentViewController: parent)
if parent == nil{
print("Back button was clicked")
}
}
其他回答
这就是我的解
extension UINavigationController: UINavigationBarDelegate {
public func navigationBar(_ navigationBar: UINavigationBar, shouldPop item: UINavigationItem) -> Bool {
if let shouldBlock = self.topViewController?.shouldPopFromNavigation() {
return shouldBlock
}
return true
}
}
extension UIViewController {
@objc func shouldPopFromNavigation() -> Bool {
return true
}
}
在你的视图控制器中,你可以这样处理:
@objc override func shouldPopFromNavigation() -> Bool {
// Your dialog, example UIAlertViewController or whatever you want
return false
}
NO
override func willMove(父控件:UIViewController?) {}
即使你在segue到覆盖这个方法的视图控制器,这个也会被调用。其中,检查parent是否为nil或not不是确保移动回正确的UIViewController的精确方法。为了准确地确定UINavigationController是否正确地导航回呈现当前的UIViewController,你将需要遵守UINavigationControllerDelegate协议。
YES
注意:MyViewController只是你想要检测返回的UIViewController的名称。
1)在你的文件顶部添加UINavigationControllerDelegate。
class MyViewController: UIViewController, UINavigationControllerDelegate {
2)添加一个属性到你的类,它将跟踪你正在segue的UIViewController。
class MyViewController: UIViewController, UINavigationControllerDelegate {
var previousViewController:UIViewController
3)在MyViewController的viewDidLoad方法中为你的UINavigationController分配self作为委托。
override func viewDidLoad() {
super.viewDidLoad()
self.navigationController?.delegate = self
}
3)在你segue之前,将之前的UIViewController分配为这个属性。
// In previous UIViewController
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "YourSegueID" {
if let nextViewController = segue.destination as? MyViewController {
nextViewController.previousViewController = self
}
}
}
4)并遵循UINavigationControllerDelegate的MyViewController中的一个方法
func navigationController(_ navigationController: UINavigationController, willShow viewController: UIViewController, animated: Bool) {
if viewController == self.previousViewController {
// You are going back
}
}
试试这个。
self.navigationItem.leftBarButtonItem?.target = "methodname"
func methodname ( ) {
// enter code here
}
这个也试试。
override func viewWillAppear(animated: Bool) {
//empty your array
}
Swift 5 __ Xcode 11.5
在我的情况下,我想做一个动画,当它完成后,返回。 一种覆盖后退按钮默认动作的方法 调用你的自定义动作是这样的:
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
setBtnBack()
}
private func setBtnBack() {
for vw in navigationController?.navigationBar.subviews ?? [] where "\(vw.classForCoder)" == "_UINavigationBarContentView" {
print("\(vw.classForCoder)")
for subVw in vw.subviews where "\(subVw.classForCoder)" == "_UIButtonBarButton" {
let ctrl = subVw as! UIControl
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
}
}
}
@objc func backBarBtnAction() {
doSomethingBeforeBack { [weak self](isEndedOk) in
if isEndedOk {
self?.navigationController?.popViewController(animated: true)
}
}
}
private func doSomethingBeforeBack(completion: @escaping (_ isEndedOk:Bool)->Void ) {
UIView.animate(withDuration: 0.25, animations: { [weak self] in
self?.vwTxt.alpha = 0
}) { (isEnded) in
completion(isEnded)
}
}
或者你可以使用这个方法一次来探索NavigationBar视图层次结构,并获得访问_UIButtonBarButton视图的索引,转换为UIControl,删除目标-动作,并添加你的自定义目标-动作:
private func debug_printSubviews(arrSubviews:[UIView]?, level:Int) {
for (i,subVw) in (arrSubviews ?? []).enumerated() {
var str = ""
for _ in 0...level {
str += "\t"
}
str += String(format: "%2d %@",i, "\(subVw.classForCoder)")
print(str)
debug_printSubviews(arrSubviews: subVw.subviews, level: level + 1)
}
}
// Set directly the indexs
private func setBtnBack_method2() {
// Remove or comment the print lines
debug_printSubviews(arrSubviews: navigationController?.navigationBar.subviews, level: 0)
let ctrl = navigationController?.navigationBar.subviews[1].subviews[0] as! UIControl
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.removeTarget(ctrl.allTargets.first, action: nil, for: .allEvents)
print("ctrl.allTargets: \(ctrl.allTargets)")
ctrl.addTarget(self, action: #selector(backBarBtnAction), for: .touchUpInside)
print("ctrl.allTargets: \(ctrl.allTargets)")
}
斯威夫特3:
override func didMove(toParentViewController parent: UIViewController?) {
super.didMove(toParentViewController: parent)
if parent == nil{
print("Back button was clicked")
}
}