I'm getting data off the server via JSON and displaying it on Labels.
I've added that method in viewDidLoad.
I want to refresh the data when the user opens the app again. Currently, even if I kill the app in the simulator and start the app again, it doesn't refresh.
I tried the viewDidAppear method, but it isn't being executed for some reason.
-(void)viewDidAppear{
NSLog(#"Called viewDidAppear");
}
This is never called. I tried to minimize the app but it didn't work.
You can listen for notifications and respond appropriately. Try using these and decide what works for your intended workflow.
UIApplicationDidBecomeActiveNotification
UIApplicationWillEnterForegroundNotification
You can use respond to the notification like this.
[[NSNotificationCenter defaultCenter] addObserverForName: UIApplicationDidBecomeActiveNotification object: nil queue: [NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
// LOAD JSON
}];
I followed this tutorial - http://leejon.es/notifying-a-viewcontroller-with-uiapplicationdidbecomeactivenotification/
First, attach to the notification in the viewWillAppear method of the target view controller:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[[NSNotificationCenter defaultCenter] addObserver: self
selector: #selector( appActivated: )
name: UIApplicationDidBecomeActiveNotification
object: nil];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[[NSNotificationCenter defaultCenter] removeObserver:self ];
}
- (void)appActivated:(NSNotification *)note
{
[self update];
}
The viewDidAppear: method takes a bool parameter wether the view was displayed with an animation which you are missing. Also you have to call the implementation of the superclass:
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear: animated];
NSLog(#"Called viewDidAppear");
}
In your app delegate implementation, there is a method called:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;
This method is called each time the app is launched, so I think it fits your needs. If you place your code here, it should work.
Also, be aware you should not perform a synchronous call here, because you will delay the app launch.
EDIT:
This method will be only called when the app launches. You could place your code inside a method, and call it from application didFinishLaunchingWithOptions, and then also call it from the method:
- (void)applicationWillEnterForeground:(UIApplication *)application;
This method will be called when the application enters the foreground, but not after the first launch, so beware.
I also think you should check the UIApplicationDelegate methods from apple developer page: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html
Also, check out the application state changes:
http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html
Related
App delegate:
- (void)applicationDidBecomeActive:(UIApplication *)application {
[[NSNotificationCenter defaultCenter] postNotificationName:APP_REFRESH_NOTIFICATION object:nil];
}
In my view controller:
- (void)viewDidLoad {
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(doStuff) postNotificationName:APP_REFRESH_NOTIFICATION object:self];
}
- (void)doStuff never gets called. Why?
I assume that you've typed your question incorrectly and you'd meant to write addObserver:selector:name:object:, instead of addObserver:selector: postNotificationName:object: (such method doesn't exist).
In the documentation of - (void)addObserver:(id)notificationObserver selector:(SEL)notificationSelector name:(NSString *)notificationName object:(id)notificationSender
we can read:
notificationSender
The object whose notifications the observer wants
to receive; that is, only notifications sent by this sender are
delivered to the observer. If you pass nil, the notification center
doesn’t use a notification’s sender to decide whether to deliver it to
the observer.
So in your case, as you're passing object:nil in postNotificationName:object:, you also have to set object:nil in addObserver:selector:name:object:.
According to the documentation you also should replace the method doStuff with:
- (void)doStuff:(NSNotification *)notification
and use #selector(doStuff:) in addObserver:selector:name:object:.
You're passing self as the object parameter to addObserver:selector:name:object:, but doStuff doesn't accept any parameters, so the method call fails (silently). Your viewDidLoad should look like this:
- (void)viewDidLoad {
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(doStuff)
name:APP_REFRESH_NOTIFICATION
object:nil];
}
You're app delegate is posting a notification when the app becomes active, but your view controller isn't subscribing to that until its view gets loaded. If your app delegate is creating your view controller and loading it (which is probable) then your controller doesn't even exist at the time the notification is posted, which is why it isn't receiving it. If you use a storyboard, and that controller is the entry point in the storyboard, AND you use the info.plist for your app to set that storyboard as the main interface, then it will have already instantiated the controller and loaded its view by the time -applicationDidBecomeActive: is called, solving your problem.
I have a View Controller in which my value is 0 (label) and when I open that View Controller from another ViewController I have set viewDidAppear to set value 20 on label. It works fine but when I close my app and than again I open my app but the value doesn't change because viewDidLoad, viewDidAppear and viewWillAppear nothing get called. How can I call when I open my app. Do I have to do anything from applicationDidBecomeActive?
Curious about the exact sequence of events, I instrumented an app as follows: (#Zohaib, you can use the NSNotificationCenter code below to answer your question).
// 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");
}
At launch, the output looks like this:
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
Enter the background then reenter the foreground:
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
Using Objective-C
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()
NotificationCenter.default.addObserver(self, selector: "doYourStuff", name: UIApplication.willEnterForegroundNotification, object: nil)
}
func doYourStuff(){
// your code
}
To remove observer you can use deinit function of swift.
deinit {
NotificationCenter.default.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.
I want to show a full page image Ad every time a UIViewController is shown.
I think I have to call the method inside a viewDidAppear or ViewWillAppear, but they are being called once.
- (void) viewDidAppear:(BOOL)animated{
[self showAds];
}
- (void) showAds{
//Do Something
}
What should I do to call a method every time a uiviewcontroller is shown( even if its already created)?
ViewWillAppear will be called every time a UIViewController is shown，but won't be called when the app is back to foreground.
you can use Notification to achieve your goal by following code,
This scenario is specially when your app is in background and user press HOME button to active it.
Register for Notifcation when your application enterForground in viewDidLoad only.
[[NSNotificationCenter defaultCenter] addObserver: self
selector: #selector(handleEnteredBackground)
name: UIApplicationDidBecomeActiveNotification
object: nil];
write a method to invoke when application enterForground
-(void)handleEnteredBackground
{
NSLog(#"%s",__FUNCTION__);
// Your stuff here
}
Dont forget to Remove Observer in viewDidUnload method
[[NSNotificationCenter defaultCenter] removeObserver:self];
Post New Notification everytime your application enterForground
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[[NSNotificationCenter defaultCenter] postNotificationName:UIApplicationDidBecomeActiveNotification object:nil];
}
ViewWillAppear should be called every time. Use:
- (void) viewWillAppear:(BOOL)animated{
[self showAds];
}
I'm developing an iOS app with latest SDK.
It's a fullscreen app.
I have a method on viewWillAppear method that has to be called every time the apps comes from background.
- (void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self setUpVideo];
}
On setUpVideo I set up AVCaptureVideoPreviewLayer because I lose the video when the apps come back from background.
As I have read, viewWillAppear isn't called when the apps come back from background and now, I don't know where to put that code.
On this question, occulus suggest to use [[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(doMyLayoutStuff:) name:UIApplicationDidChangeStatusBarFrameNotification object:nil]; but it doesn't work for me.
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(setUpVideo:) name:UIApplicationDidChangeStatusBarFrameNotification object:nil];
}
Any advice?
Observe UIApplicationWillEnterForegroundNotification instead.
- (void)viewDidAppear {
[super viewDidAppear];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(enterForeground:)
name:UIApplicationWillEnterForegroundNotification
object:nil];
// ...
}
- (void)enterForeground:(NSNotification *)notification {
// do stuff
}
Don't call viewWillAppear: directly from the enterForeground: method. Instead move all required code to a separate method and call that from both viewWillAppear: and enterForeground:.
applicationWillEnterForeground will trigger when app comes from background
- (void)applicationWillEnterForeground:(UIApplication *)application
{
// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
}
Additionally, you can use UIApplicationDidBecomeActiveNotification for firing some method
[[NSNotificationCenter defaultCenter] addObserver: self
selector: #selector(handleMethod:)
name: UIApplicationDidBecomeActiveNotification
object: [UIApplication sharedApplication]];
Try posting this notification from
- (void)applicationDidBecomeActive:(UIApplication *)application of AppDelegate(or observe corresponding notification which is better)
I add this function to post a notification when the app enter foreground:
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[[NSNotificationCenter defaultCenter] postNotificationName: #"UIApplicationWillEnterForegroundNotification" object: nil];
}
In my own class:
- (void) handleEnterForeground: (NSNotification*) sender
{
[self reloadTableData];
}
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver: self
selector: #selector(handleEnterForeground:)
name: #"UIApplicationWillEnterForegroundNotification"
object: nil];
}
but the handleEnterForeground: function will called twice, I don't know why. The
reloadTableData: function will call remote webService , so when the app enter
foreground, it will stuck for a while.
The system will call that event automatically. The reason it fires twice is because you manually fire it again.
P.S. It's better to use the variable name UIApplicationWillEnterForeground, instead of a NSString literal.
EDIT: I realize now the confusion is coming from the fact that you didn't know that this even name was already taken. As a note to other people who run into this kind of problem, it is a good practice to prefix your event names with your project prefix (i.e. XYZEventNotification) to avoid collisions.