I have 2 observers registered. One of them is in appDelegate and the other is in myViewController. When I am in myViewController, I just expect to get two notifications, one from appDelegate which executes some method globally, the other one from myViewController which executes some other method. But, only the one in appDelegate gets called. If I remove the observer in appDelegate, the observer in myViewController gets called. Actually, I can just use the observer method in appDelegate and find out the current view controller and execute the code of the method in myViewController. But, I just don't wanna mess appDelegate. The same code for both of them but I remove the observer in myViewController when viewWillDisappear() method gets called. Any ideas? Thanks.
appDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(someMethod:)
name:#"someName"
object:nil];
}
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo
{
[[NSNotificationCenter defaultCenter] postNotificationName:#"someName"
object:nil
userInfo:someUserInfo];
}
- (void)someMethod:(NSNotification *)notification
{
// gets called
}
myViewController
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(someMethod:)
name:#"someName"
object:nil];
}
- (void)viewWillDisappear:(BOOL)animated
{
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"someName"
object:nil];
[super viewWillDisappear:animated];
}
- (void)someMethod:(NSNotification *)notification
{
// not called
}
In the code below you're posting before observing
(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[[NSNotificationCenter defaultCenter] postNotificationName:#"someName"
object:nil
userInfo:someUserInfo];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(someMethod:)
name:#"someName"
object:nil];
}
* Original *
Plenty of possible issues here:
one the notification Name could be spelt wrong = #"someName" - If this is going to be observe red from other classes, think about creating an
in a .h (that both classes import)
include
extern NSString * const XXXSomeNameForSomeNotification;
in the corresponding .m
NSString * const XXXSomeNameForSomeNotification = #"someName";
That's one way to ensure they're all observing/posting the right notification
If that's not your issue then try adding observing the notification from the viewDidLoad or another method that's called prior to viewDidAppear as it could be that it's not observing you notification when it's actually posted. Add break points to observe this.
Looks like, Your notification is posted before view is loaded. See adding some logs.
OR try this -
double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
[[NSNotificationCenter defaultCenter] postNotificationName:#"someName"
object:nil
userInfo:someUserInfo];
});
I think as per you posted code the reason is
- (void)viewWillDisappear:(BOOL)animated
{
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"someName"
object:nil];
[super viewWillDisappear:animated];
}
The method above will remove the notification observing if the current view is not on screen.
Also you may want to move the
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"someName"
object:nil];
to
- (void) dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"someName"
object:nil];
}
that way you only stop observing the notification when you remove the view controller form memory. You may want to check in the method that's called if you're on screen.
Related
This is my code.
Here create the observer to Notification called Example into ViewController
- (void)addObserverExample
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(example:)
name:#"Example"
object:nil];
}
- (void)example:(NSNotification *)notification{
NSLog(#"Example!!!");
}
From viewDidLoad register my observer
- (void)viewDidLoad
{
[self addObserverExample];
}
In my second ViewController. When tapped a button excute this code:
[[NSNotificationCenter defaultCenter] postNotificationName:#"Example" object:self.dictKeys userInfo:nil];
The problem I have is that the notification is never executed.
Any idea.
Have created demo for NSNotificationCenter as per your question and it's working fine for me. Here it is the link of that code: NSNotificationCenter Demo
- (void)viewDidLoad {
[super viewDidLoad];
[self addObserverExample];
}
- (void)addObserverExample
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(example:)
name:#"Example"
object:nil];
}
- (void)example:(NSNotification *)notification{
NSLog(#"Example!!!");
NSLog(#"%#",notification.userInfo);
}
- (IBAction)btnFireNotification:(id)sender {
[[NSNotificationCenter defaultCenter] postNotificationName:#"Example" object:nil userInfo:#{#"key" : #"value"}];
}
I believe the problem you're having may be related to the fact that in your second view controller, you're passing self.dictKeys in the object parameter.
If you want to pass data via the NSNotificationCenter, you should use the userInfo parameter instead.
Darshan's example does this the correct way.
I am facing an issue with NSNotificationCenter.
I am not able to send message and receive message using NSNotificationCenter in latest ios 8.4 (XCode 6.4)
Please check the following code:
1) I want to send data using first view controller to another view.
so i have written the following code in first viewcontroller:
When user btn clicked method as following :
- (IBAction)btnClicked:(id)sender
{
[self postNotification];
[self performSegueWithIdentifier:#"asGo" sender:self];
}
-(void)postNotification{
[[NSNotificationCenter defaultCenter] postNotificationName:#"MyNotification" object:self];
}
2) In Second view controller i have added observer in ViewWillApper as following :
-(void) viewWillAppear:(BOOL)animated
{
[super viewWillAppear:YES];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(eventListenerDidReceiveNotification:)
name:#"MyNotification"
object:nil];
}
-(void)eventListenerDidReceiveNotification:(NSNotification*)txt
{
NSLog(#"i got notfication:");
}
so eventListenerDidReceiveNotification is not called while come on view.
But i am not getting above log while i come on second vc with navigation
As others have noted, NSNotificationCenter doesn't work like a post office. It only delivers notifications if someone actually listens to them at the moment they arrived. This is the reason your eventListenerDidReceiveNotification method is not being called: you add an observer in viewWillAppear, which is called after the segue (I assume that you're using segues because of the performSegueWithIdentifier method in your code) is finished, so it's definitely called after postNotification has been called.
So, in order to pass data via NSNotificationCenter you have to add an observer before you post a notification.
The following code is completely useless and unnecessarily overcomplicated, you shouldn't do anything like that, but since you keep insisting on using a scheme like this, here you go:
//Didn't test this code. Didn't even compile it, to be honest, but it should be enough to get the idea.
NSString * const SOUselessNotificationName = #"MyUselessNotification";
#pragma mark - FIRST VC
#interface SOFirstVC : UIViewController
#end
#implementation SOFirstVC
NSString * const SOasGoSegueIdentifer = #"asGo";
- (IBAction)btnClicked:(id)sender {
[self performSegueWithIdentifier:SOasGoSegueIdentifer sender:self];
}
-(void)postNotification {
[[NSNotificationCenter defaultCenter] postNotificationName:SOUselessNotificationName object:self];
}
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
if ([segue.identifer isEqualToString:SOasGoSegueIdentifer]) {
SOSecondVC *destinationVC = (SOSecondVC *)segue.destinationViewController;
[destinationVC registerToReceiveNotificationsFromObject:self];
[self postNotification];
}
}
#end
#pragma mark - SECOND VC
#interface SOSecondVC : UIViewController
-(void)registerToReceiveNotificationsFromObject:(id)object;
#end
#implementation SOSecondVC
-(void)registerToReceiveNotificationsFromObject:(id)object {
[[NSNotificationCenter defaultCenter] addObserver:self selector:(eventListenerDidReceiveUselessNotification:) name:SOUselessNotificationName object:object];
}
-(void)eventListenerDidReceiveUselessNotification:(NSNotification*)uselessNotification {
NSLog(#"I got a useless notfication! Yay!");
}
-(void)dealloc {
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
#end
NSNotificationCenter basically has 3 steps
Adding Observer like [[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(open:) name:#"OpenDetail" object:nil];
Posting Notification [[NSNotificationCenter defaultCenter] postNotificationName:#"OpenDetail" object:self];
Removing Observer [[NSNotificationCenter defaultCenter] removeObserver:self name:#"OpenDetail" object:nil];
I think you are posting your notification and then later adding observer while it's vie versa. You have to add observer first then post notification.
HTH
First you have to setup the data you want to send
NSDictionary *userInfo = [NSDictionary dictionaryWithObject:myObject forKey:#"aKey"];
Then you post it with the data like so:
[[NSNotificationCenter defaultCenter] postNotificationName: #"MyNotification" object:nil userInfo:userInfo];
And finally you read the data off the notification:
-(void)eventListenerDidReceiveNotification:(NSNotification*)notification
{
NSLog(#"i got notification:");
NSDictionary *userInfo = notification.userInfo;
NSString *myObject = [userInfo objectForKey:#"aKey"];
}
I have a simple application as RSS-reader.
How do I better organize to update feed when receiving Push Notification?
1) Call FirstViewController from didReceiveRemoteNotification and update feed?
2) Send value from didReceiveRemoteNotification to FirstViewController, and in FirstViewController update feed?
I'm posting NSNotification from AppDelegate
- (void)application:(UIApplication *)application
didReceiveRemoteNotification:(NSDictionary *)userInfo
{
[[NSNotificationCenter defaultCenter]
postNotificationName:#"appDidReceiveRemoteNotification"
object:self
userInfo:userInfo];
}
And listening to that notification in my ViewControllers, like this
- (void)remoteNotificationReceived:(NSNotification *)aNotification
{
NSDictionary *userInfo = aNotification.userInfo;
// Update your views here
}
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(remoteNotificationReceived:)
name:#"appDidReceiveRemoteNotification"
object:nil];
}
- (void)dealloc
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
I have the following code within AppDelegate. The purpose being to create a couple of observers, and then call some code. Once that code completes it then posts a notification, and the observer should then remove both observers and call the completion handler.
My issue is that it appears that the observers are not being removed as I expected. The notification is posted, and the NSLog entry is written to console, so I know that the observer is working. However, on the second time of calling, the NSLog is called twice, third time three times etc.
My thoughts are that this is to do with the removal being within the block of code that is running from the observer, however, I am unsure how I can resolve this (if indeed this is what the issue is).
Could someone be so kind as to explain how I can achieve this?
Thanks.
-(void) application:(UIApplication *)application performFetchWithCompletionHandler:
(void (^)(UIBackgroundFetchResult))completionHandler {
[[NSNotificationCenter defaultCenter] addObserverForName:#"fetchDidCompleteNewData" object:nil
queue:nil usingBlock:^(NSNotification *completed) {
//Remove Observers
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"fetchDidCompleteNewData"
object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"fetchDidCompleteNoData"
object:nil];
// Post completion
completionHandler(UIBackgroundFetchResultNewData);
NSLog(#"Background fetch completed... New Data");
}];
[[NSNotificationCenter defaultCenter] addObserverForName:#"fetchDidCompleteNoData" object:nil
queue:nil usingBlock:^(NSNotification *completed) {
//Remove Observers
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"fetchDidCompleteNoData"
object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self
name:#"fetchDidCompleteNewData"
object:nil];
//post completion
completionHandler(UIBackgroundFetchResultNoData);
NSLog(#"Background fetch completed... No New Data");
}];
GetDetails *getDetails = [[GetDetails alloc] init];
[getDetails backgroundRefresh];
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:UIApplicationBackgroundFetchIntervalMinimum];
return YES;
}
You are not registering self as an object. Moreover, when the block is pushed onto the stack by addObserverForName: the method has not yet returned so the notification is nil.
Make a global object using block, eg
__block __weak id notification;
then,
notification = [[NSNotificationCenter defaultCenter] addObserverForName:#"fetchDidCompleteNewData" object:nil queue:nil usingBlock:^(NSNotification *completed) {
//Remove Observers
[[NSNotificationCenter defaultCenter] removeObserver:notification];
}];
My thoughts are that this is to do with the removal being within the
block of code that is running from the observer, however, I am unsure
how I can resolve this (if indeed this is what the issue is).
Could someone be so kind as to explain how I can achieve this?
Certainly.
You can easily test your theory by not using the addObserverForName:object:queue:usingBlock: method and instead using the addObserver:selector:name:object: method, where the selector is the name of a function you call instead of using a block.
Simply use the API guide for NSNotificationCenter for details about these methods, or in general, since you question was about what other method you could use that does not require a block statement, consulting the API is the first place to check for alternative tools within the class.
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)