后台打开应用时不调用ViewDidAppear
后台打开应用时不调用ViewDidAppear
提问于 2013-04-07 23:52:36
我有一个视图控制器，其中我的值是0(标签)，当我从另一个ViewController打开这个视图控制器时，我已经将viewDidAppear设置为标签上的值20。它工作得很好，但当我关闭我的应用程序，然后再次打开我的应用程序，但值不会改变，因为viewDidLoad，viewDidAppear和viewWillAppear什么都不会被调用。当我打开我的应用程序时，我如何呼叫。我需要从applicationDidBecomeActive做些什么吗？
回答 6
Stack Overflow用户
回答已采纳
发布于 2013-04-08 00:32:50
出于对事件的确切顺序的好奇，我检测了一个应用程序，如下所示：(@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进入背景，然后重新进入前台：
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 notificationStack Overflow用户
发布于 2017-07-13 03:54:15
Swift 3.0 ++版本
在您的viewDidLoad中，在通知中心注册以收听从后台打开的操作
NotificationCenter.default.addObserver(self, selector:#selector(doSomething), name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)然后添加此函数并执行所需的操作
func doSomething(){
//...
}最后，添加此函数，以便在视图控制器被销毁时清理通知观察者。
deinit {
NotificationCenter.default.removeObserver(self)
}Stack Overflow用户
发布于 2018-11-26 22:36:55
Swift 4.2。版本
在viewDidLoad中注册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，您可以移除观察者。这仅在iOS9和macOS 10.11版本中是必需的
deinit {
NotificationCenter.default.removeObserver(self)
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/15864364
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