8 回答

• 121

  Using Objective-C

  您应该在 ViewController 的 viewDidLoad 方法中注册 UIApplicationWillEnterForegroundNotification ，每当应用程序从后台返回时，您可以在注册通知的方法中执行任何操作 . 当应用程序从后台返回到前台时，将不会调用 ViewController 的 viewWillAppear 或 viewDidAppear .

  -(void)viewDidLoad{
  
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(doYourStuff)
  
    name:UIApplicationWillEnterForegroundNotification object:nil];
  }
  
  -(void)doYourStuff{
  
     // do whatever you want to do when app comes back from background.
  }
  

  不要忘记取消注册您注册的通知 .

  -(void)dealloc {
      [[NSNotificationCenter defaultCenter] removeObserver:self];
  }
  

  Note 如果您为 UIApplicationDidBecomeActiveNotification 注册 viewController ，则每次应用程序生效时都会调用您的方法，不建议为此通知注册 viewController .

  Using Swift

  要添加观察者，您可以使用以下代码

  override func viewDidLoad() {
      super.viewDidLoad()
  
       NSNotificationCenter.defaultCenter().addObserver(self, selector:"doYourStuff", name:
       UIApplicationWillEnterForegroundNotification, object: nil)
   }
  
   func doYourStuff(){
       // your code
   }
  

  要删除观察者，您可以使用swift的deinit函数 .

  deinit {
      NSNotificationCenter.defaultCenter().removeObserver(self)
  }
  

  回复于 2024-04-30T05:09:41+08:00
• 2

  Swift 4.2 . 版

  在 viewDidLoad 注册NotificationCenter，以便在应用程序从后台返回时收到通知

  NotificationCenter.default.addObserver(self, selector: #selector(doSomething), name: UIApplication.willEnterForegroundNotification, object: nil)
  

  实现应该调用的方法 .

  @objc private func doSomething() {
      // Do whatever you want, for example update your view.
  }
  

  一旦 ViewController 被销毁，您可以删除观察者 . 这仅在iOS9和macOS 10.11下方需要

  deinit {
      NotificationCenter.default.removeObserver(self)
  }
  

  回复于 2024-04-30T05:09:41+08:00
• 1

  尝试在AppDelegate applicationWillEnterForeground中添加它 .

  func applicationWillEnterForeground(_ application: UIApplication) {        
      // makes viewWillAppear run
      self.window?.rootViewController?.beginAppearanceTransition(true, animated: false)
      self.window?.rootViewController?.endAppearanceTransition()
  }
  

  回复于 2024-04-30T05:09:41+08:00
• 289

  根据Apple的文档：

  (void)beginAppearanceTransition:(BOOL)isAppearing animated:(BOOL)animated;
  

  Description:
  告诉儿童控制器它的外观即将改变 . 如果要实现自定义容器控制器，请使用此方法告诉子项其视图即将为 appear or disappear . Do not invoke viewWillAppear:, viewWillDisappear:, viewDidAppear:, or viewDidDisappear: directly .

  (void)endAppearanceTransition;
  

  Description:

  告诉儿童控制器它的外观已经改变 . 如果要实现自定义容器控制器，请使用此方法告诉子项视图转换已完成 .

  Sample code:

  (void)applicationDidEnterBackground:(UIApplication *)application
  {
  
      [self.window.rootViewController beginAppearanceTransition: NO animated: NO];  // I commented this line
  
      [self.window.rootViewController endAppearanceTransition]; // I commented this line
  
  }
  

  问题： How I fixed?

  Ans ：我在申请中发现了这条线 . 这条线使我的应用程序无法收到任何ViewWillAppear通知 . When I commented these lines it's working fine .

  回复于 2024-04-30T05:09:41+08:00
• 0

  Swift 3.0版

  在 viewDidLoad 中，在通知中心注册以收听从后台操作打开的内容

  NotificationCenter.default.addObserver(self, selector:#selector(doSomething), name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
  

  然后添加此功能并执行所需的操作

  func doSomething(){
      //...
  }
  

  最后添加此函数以在视图控制器被销毁时清理通知观察器 .

  deinit {
      NotificationCenter.default.removeObserver(self)
  }
  

  回复于 2024-04-30T05:09:41+08:00
• 36

  对事件的确切顺序感到好奇，我按如下方式对应用程序进行了检测：（@ Zohaib，您可以使用下面的NSNotificationCenter代码来回答您的问题） .

  // AppDelegate.m
  
  - (void)applicationWillEnterForeground:(UIApplication *)application
  {
      NSLog(@"app will enter foreground");
  }
  
  - (void)applicationDidBecomeActive:(UIApplication *)application
  {
      NSLog(@"app did become active");
  }
  
  // ViewController.m
  
  - (void)viewDidLoad
  {
      [super viewDidLoad];
      NSLog(@"view did load");
  
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
      [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForeground:) name:UIApplicationWillEnterForegroundNotification object:nil];
  }
  
  - (void)appDidBecomeActive:(NSNotification *)notification {
      NSLog(@"did become active notification");
  }
  
  - (void)appWillEnterForeground:(NSNotification *)notification {
      NSLog(@"will enter foreground notification");
  }
  
  - (void)viewWillAppear:(BOOL)animated {
      [super viewWillAppear:animated];
      NSLog(@"view will appear");
  }
  
  - (void)viewDidAppear:(BOOL)animated {
      [super viewDidAppear:animated];
      NSLog(@"view did appear");
  }
  

  在启动时，输出如下所示：

  2013-04-07 09:31:06.505 myapp[15459:11303] view did load
  2013-04-07 09:31:06.507 myapp[15459:11303] view will appear
  2013-04-07 09:31:06.511 myapp[15459:11303] app did become active
  2013-04-07 09:31:06.512 myapp[15459:11303] did become active notification
  2013-04-07 09:31:06.517 myapp[15459:11303] view did appear
  

  输入背景然后重新进入前景：

  2013-04-07 09:32:05.923 myapp[15459:11303] app will enter foreground
  2013-04-07 09:32:05.924 myapp[15459:11303] will enter foreground notification
  2013-04-07 09:32:05.925 myapp[15459:11303] app did become active
  2013-04-07 09:32:05.926 myapp[15459:11303] did become active notification
  

  回复于 2024-04-30T05:09:41+08:00
• 3

  我认为注册UIApplicationWillEnterForegroundNotification是有风险的，因为你最终可能会有多个控制器对该通知作出反应 . 收到通知后，这些控制器仍然可见，这些都没有任何保证 .

  这是我的工作：我直接从App的委托didBecomeActive方法强制在活动控制器上调用viewDidAppear：

  将以下代码添加到 - (void)applicationDidBecomeActive:(UIApplication *)application

  UIViewController *activeController = window.rootViewController;
  if ([activeController isKindOfClass:[UINavigationController class]]) {
      activeController = [(UINavigationController*)window.rootViewController topViewController];
  }
  [activeController viewDidAppear:NO];
  

  回复于 2024-04-30T05:09:41+08:00
• 4

  只需让您的视图控制器注册 UIApplicationWillEnterForegroundNotification 通知并做出相应的反应 .

  回复于 2024-04-30T05:09:41+08:00