检测何时在导航栏上按下“后退”按钮

Question

在导航栏上按下后退按钮（返回上一屏幕，返回到父视图）时，我需要执行一些操作。

有什么我可以实现的方法来捕获事件并触发一些操作以在屏幕消失之前暂停并保存数据？

Answer 1

根据一些评论，原始答案中的解决方案在iOS 8+中的某些情况下似乎不起作用。如果没有更多详细信息，我无法验证实际情况。对于那些在那种情况下的人，还有另一种选择。可以通过覆盖检测何时弹出视图控制器willMove(toParentViewController:)。基本思想是在parentis 时弹出视图控制器nil。请查看“实现Container View Controller”以了解更多详细信息。从iOS 5开始，我发现处理这种情况的最简单方法是使用新方法- (BOOL)isMovingFromParentViewController：- (void)viewWillDisappear:(BOOL)animated {  [super viewWillDisappear:animated];  if (self.isMovingFromParentViewController) {    // Do your stuff here  }}- (BOOL)isMovingFromParentViewController 当您在导航堆栈中推入和弹出控制器时很有意义。但是，如果要呈现模式视图控制器，则应- (BOOL)isBeingDismissed改用：- (void)viewWillDisappear:(BOOL)animated {  [super viewWillDisappear:animated];  if (self.isBeingDismissed) {    // Do your stuff here  }}如本问题所述，您可以结合使用以下两个属性：- (void)viewWillDisappear:(BOOL)animated {  [super viewWillDisappear:animated];  if (self.isMovingFromParentViewController || self.isBeingDismissed) {    // Do your stuff here  }}其他解决方案依赖于的存在UINavigationBar。相反，更喜欢我的方法，因为它使执行任务所需的任务与触发事件的操作（即按后退按钮）分离。

Answer 2

虽然viewWillAppear()和viewDidDisappear() 被当返回按钮被窃听叫，它们也被称为在其他时间。有关更多信息，请参见答案结尾。使用UIViewController.parent当借助willMoveToParentViewController(_:)OR 将VC从其父级（NavigationController）中删除时，最好检测到后退按钮didMoveToParentViewController()如果parent为零，则将视图控制器从导航堆栈中弹出并关闭。如果parent不为nil，则将其添加到堆栈中并显示。// Objective-C-(void)willMoveToParentViewController:(UIViewController *)parent {&nbsp; &nbsp; &nbsp;[super willMoveToParentViewController:parent];&nbsp; &nbsp; if (!parent){&nbsp; &nbsp; &nbsp; &nbsp;// The back button was pressed or interactive gesture used&nbsp; &nbsp; }}// Swiftoverride func willMove(toParent parent: UIViewController?) {&nbsp; &nbsp; super.willMove(toParent: parent)&nbsp; &nbsp; if parent == nil {&nbsp; &nbsp; &nbsp; &nbsp; // The back button was pressed or interactive gesture used&nbsp; &nbsp; }}换出willMove了didMove和检查self.parent做工作后视图控制器被驳回。停止解雇请注意，如果需要执行某种异步保存，则检查父级不允许您“暂停”过渡。为此，您可以实现以下内容。唯一的缺点是，您失去了精美的iOS样式/动画后退按钮。在此处也要小心使用交互式滑动手势。使用以下内容处理这种情况。var backButton : UIBarButtonItem!override func viewDidLoad() {&nbsp; &nbsp; super.viewDidLoad()&nbsp; &nbsp; &nbsp;// Disable the swipe to make sure you get your chance to save&nbsp; &nbsp; &nbsp;self.navigationController?.interactivePopGestureRecognizer.enabled = false&nbsp; &nbsp; &nbsp;// Replace the default back button&nbsp; &nbsp; self.navigationItem.setHidesBackButton(true, animated: false)&nbsp; &nbsp; self.backButton = UIBarButtonItem(title: "Back", style: UIBarButtonItemStyle.Plain, target: self, action: "goBack")&nbsp; &nbsp; self.navigationItem.leftBarButtonItem = backButton}// Then handle the button selectionfunc goBack() {&nbsp; &nbsp; // Here we just remove the back button, you could also disabled it or better yet show an activityIndicator&nbsp; &nbsp; self.navigationItem.leftBarButtonItem = nil&nbsp; &nbsp; someData.saveInBackground { (success, error) -> Void in&nbsp; &nbsp; &nbsp; &nbsp; if success {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self.navigationController?.popViewControllerAnimated(true)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Don't forget to re-enable the interactive gesture&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self.navigationController?.interactivePopGestureRecognizer.enabled = true&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; self.navigationItem.leftBarButtonItem = self.backButton&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; // Handle the error&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }}将显示更多视图如果您没有遇到viewWillAppear viewDidDisappear问题，我们来看一个例子。假设您有三个视图控制器：ListVC：事物的表视图DetailVC：关于事物的详细信息SettingsVC：某些选项detailVC当您从listVC转到settingsVC并返回到时，可以跟踪上的呼叫listVC列表>详细信息（按下detailVC）Detail.viewDidAppear<-出现详细信息>设置（按下settingsVC）Detail.viewDidDisappear<-消失然后回头...设置>详细信息（弹出设置 VC）<- Detail.viewDidAppear出现详细信息>列表（弹出详细信息 VC）Detail.viewDidDisappear<-消失请注意，viewDidDisappear不仅在返回时，而且在前进时，都会多次调用它。对于可能需要的快速操作，但是对于更复杂的操作（例如要保存的网络呼叫），可能不需要。

Answer 3

第一种方法- (void)didMoveToParentViewController:(UIViewController *)parent{&nbsp; &nbsp; if (![parent isEqual:self.parentViewController]) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;NSLog(@"Back pressed");&nbsp; &nbsp; }}第二种方法-(void) viewWillDisappear:(BOOL)animated {&nbsp; &nbsp; if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound) {&nbsp; &nbsp; &nbsp; &nbsp;// back button was pressed.&nbsp; We know this is true because self is no longer&nbsp; &nbsp; &nbsp; &nbsp;// in the navigation stack.&nbsp;&nbsp;&nbsp; &nbsp; }&nbsp; &nbsp; [super viewWillDisappear:animated];}