백그라운드에서 앱을 열 때 ViewDidAppear가 호출되지 않습니다

백그라운드에서 앱을 열 때 ViewDidAppear가 호출되지 않습니다

---

나는 나의 값이 0 (라벨) 때 내가보기 컨트롤러가 서로 개폐되는 뷰 컨트롤러가 ViewController내가 설정 한 viewDidAppear라벨에 설정 값 (20)을. 그것은 잘 작동하지만 난 내 응용 프로그램을 종료하지 않고 다시 내 응용 프로그램을 열보다하지만 값이 있기 때문에 변경하지 않을 때 viewDidLoad, viewDidAppear그리고 viewWillAppear아무것도 전화를받을. 앱을 열 때 어떻게 전화를 걸 수 있습니까? 내가해야 할 일이 applicationDidBecomeActive있습니까?

---

정확한 이벤트 순서에 대해 궁금한 점은 다음과 같이 앱을 계측 한 것입니다. (@Zohaib, 아래 NSNotificationCenter 코드를 사용하여 질문에 답변 할 수 있습니다).

// 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");
}

시작시 출력은 다음과 같습니다.

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

배경을 입력 한 다음 전경을 다시 입력하십시오.

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

---

Objective-C 사용

You should register a UIApplicationWillEnterForegroundNotification in your ViewController's viewDidLoad method and whenever app comes back from background you can do whatever you want to do in the method registered for notification. ViewController's viewWillAppear or viewDidAppear won't be called when app comes back from background to foreground.

-(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.
}

Don't forget to unregister the notification you are registered for.

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

Note if you register your viewController for UIApplicationDidBecomeActiveNotification then your method would be called every time your app becomes active, It is not recommended to register viewController for this notification .

Using Swift

For adding observer you can use the following code

 override func viewDidLoad() {
    super.viewDidLoad()

     NSNotificationCenter.defaultCenter().addObserver(self, selector:"doYourStuff", name:
     UIApplicationWillEnterForegroundNotification, object: nil)
 }

 func doYourStuff(){
     // your code
 }

To remove observer you can use deinit function of swift.

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

---

Swift 3.0 ++ version

In your viewDidLoad, register at notification center to listen to this opened from background action

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

Then add this function and perform needed action

func doSomething(){
    //...
}

Finally add this function to clean up the notification observer when your view controller is destroyed.

deinit {
    NotificationCenter.default.removeObserver(self)
}

---

Swift 4.2. version

Register with the NotificationCenter in viewDidLoad to be notified when the app returns from background

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

Implement the method that should be called.

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

You can remove the observer once the ViewController is destroyed. This is only required below iOS9 and macOS 10.11

deinit {
    NotificationCenter.default.removeObserver(self)
}

---

Just have your view controller register for the UIApplicationWillEnterForegroundNotification notification and react accordingly.

---

I think registering for the UIApplicationWillEnterForegroundNotification is risky as you may end up with more than one controller reacting to that notification. Nothing garanties that these controllers are still visible when the notification is received.

Here is what I do: I force call viewDidAppear on the active controller directly from the App's delegate didBecomeActive method:

Add the code below to - (void)applicationDidBecomeActive:(UIApplication *)application

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

---

try adding this in AppDelegate applicationWillEnterForeground.

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

---

As per Apple's documentation:

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

Description:
Tells a child controller its appearance is about to change. If you are implementing a custom container controller, use this method to tell the child that its views are about to appear or disappear. Do not invoke viewWillAppear:, viewWillDisappear:, viewDidAppear:, or viewDidDisappear: directly.

(void)endAppearanceTransition;

Description:

Tells a child controller its appearance has changed. If you are implementing a custom container controller, use this method to tell the child that the view transition is complete.

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

}

Question: How I fixed?

Ans: I found this piece of lines in application. This lines made my app not recieving any ViewWillAppear notification's. When I commented these lines it's working fine.

참고URL : https://stackoverflow.com/questions/15864364/viewdidappear-is-not-called-when-opening-app-from-background