I am just coding my first iOS app using a today widget (using Swift). I was wondering if there is a function that is called whenever my app comes back to the foreground after dismissing the notification center.
I know I can use an Observer to check for UIApplicationWillEnterForegroundNotification but my function does not get called when pulling down the notification center while using my app and dismissing it again.
My problem is simple:
It is quite unlikely users will pull down the notification center to manipulate data I am using in the app, but I still have to consider what happens if they do. The user is supposed to be able to save his current location by pressing the today widget button.
If that happens while using my app, the app won't check for new data.
I used the following code for determining if the notification center was opened during the application's run time:
#import "ViewController.h"
#interface ViewController ()
#end
#implementation ViewController
{
BOOL notificationCenterCurrentlyDisplayed;
}
- (void) viewDidLoad
{
[super viewDidLoad];
notificationCenterCurrentlyDisplayed = false;
NSNotificationCenter *defaultCenter = [NSNotificationCenter defaultCenter];
[defaultCenter addObserver:self selector:#selector(onNotificationCenterDisplayed) name:UIApplicationWillResignActiveNotification object:nil];
[defaultCenter addObserver:self selector:#selector(onNotificationCenterDismissed) name:UIApplicationDidBecomeActiveNotification object:nil];
}
- (void) onNotificationCenterDisplayed
{
notificationCenterCurrentlyDisplayed = true;
NSLog(#"Notification center has been displayed!");
}
- (void) onNotificationCenterDismissed
{
// Reason for this check is because once the app is launched the UIApplucationDidBecomeActiveNotification is called.
if (notificationCenterCurrentlyDisplayed)
{
notificationCenterCurrentlyDisplayed = false;
NSLog(#"Notification center has been dismissed!");
}
}
#end
Also the notification center was displayed method will also be called when the user decides to close the application into the background.
Related
I bult an iOS app and in -(void)viewDidLoad I parse data from web, and display it on load. But often when I open my app it displays old data(app loads fast) and I need to kill it and open it again, after that it parses data and shows new. Why is that happening?
It doesn't work that way because viewDidLoad is only called once, when the view is created. After backgrounding and returning, your view still exists.
If you want to reload your data whenever the app returns from the background, you need to either override applicationDidBecomeActive: in your UIApplicationDelegate implementation, or you need to listen for the appropriate notification:
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(applicationDidBecomeActive:)
name:UIApplicationDidBecomeActiveNotification
object:nil];
}
- (void)applicationDidBecomeActive:(NSNotification *)notification
{
// reload your data here.
}
Don't forget to remove yourself as an observer when you no longer need the notification.
I am creating an app with functionality like a stopwatch. When the app moves to the background, iOS takes a snapshot, and when it moves back into the foreground it uses that snapshot for the animation while switching back to the app.
This means that if the app was backgrounded for 10 seconds, the stopwatch will have the wrong time (by 10 seconds) displayed during the opening animation.
Is there some way to stop iOS taking this snapshot, or stop iOS from using it when the app moves back to the foreground?
You can not stop iOS from taking snapshot.
But you can display and hide a temporary view using below notifications :
UIApplicationDidEnterBackgroundNotification
UIApplicationWillEnterForegroundNotification
The temporary view will be then taken as the snapshot.
[[NSNotificationCenter defaultCenter]addObserver:self selector:#selector(displayTempView) name:UIApplicationDidEnterBackgroundNotification object:nil];
[[NSNotificationCenter defaultCenter]addObserver:self selector:#selector(hideTempView) name:UIApplicationWillEnterForegroundNotification object:nil];
- (void) displayTempView {
tempWebView.hidden = NO;
}
- (void) hideTempView {
tempWebView.hidden = YES;
}
Hope it helps.
I am using push notifications in my code and whenever a notification comes, I want to update the value of a label in another ViewController.
My code in AppDelegate is:
- (void)addMessageFromRemoteNotification:(NSDictionary*)userInfo updateUI:(BOOL)updateUI
{
NSLog(#"Notification arrived");
//[mydeals setCode1_id:mydeals.code1_id withString:#"123456"];
mydeals=[[MyDealsViewController alloc]init];
NSDictionary* codeDetails=[[NSDictionary alloc] initWithObjectsAndKeys:#"123456",#"Code_id", nil];
[[NSNotificationCenter defaultCenter] postNotificationName:#"CodeArrived" object:self userInfo:codeDetails];
}
then in my other view controller I have this code:
#implementation MyDealsViewController
-(id) init
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(receiveCode:)
name:#"CodeArrived"
object:nil];
return self;
}
-(void) receiveCode:(NSNotification*)notification
{
NSLog(#"received Code: %#",notification.userInfo);
self.code1_id.text=[NSString stringWithFormat:#"%#",[[notification userInfo] valueForKey:#"Code_id"]];
}
the log is printed correctly but when I manually go into that screen I see the default value, like the label is not updated at all. What should I do?
You have to make sure that when you "manually go" to MyDealsViewController, whatever how you do it, it got to be the same instance of MyDealsViewController wich has been called receiveCode. Otherwise it's going to init with it's default values.
You might also try calling [self.code1_id setNeedsLayout];
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];
}