I can add observer twice (by accident) to the notification center and I will get notifications twice.
Is it possible to get only one notification? Do you know more elegant solutions?
I show you this example because this may lead to bugs.
- (void)viewDidLoad
{
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardDidShow:)
name:UIKeyboardDidShowNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardDidShow:)
name:UIKeyboardDidShowNotification
object:nil];
}
- (void)keyboardDidShow:(NSNotification *)ntf
{
}
If you're not sure if you added the observer somewhere else, you can use the following code everytime you're adding an Observer
[[NSNotificationCenter defaultCenter] removeObserver:self name:aName object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:aSelector name:aName object:nil];
This way you are removing the old one (if it existed) and adding a new one.
It's not 100% fail proof but it's a start. This could fail in Multi-Threaded apps where the calls are being made async or other unique situations.
You can also set an object to nil and then later use that object as if was still valid.
Not everything can be made fail safe.
Related
In my application I am loading some webpages embedded with Photos and Videos. Also I am using the following notifications to manage the player,
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(embeddedVideoStarted:) name:#"UIMoviePlayerControllerDidEnterFullscreenNotification" object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(embeddedVideoEnded:) name:#"UIMoviePlayerControllerWillExitFullscreenNotification" object:nil];
This is working fine in iOS7, but in iOS8 its not working. Any workarounds? Thanks in advance.
This is one option, I have found.. The problem is that is not Will is DID become hidden..
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(embeddedVideoStarted:)
name:UIWindowDidBecomeVisibleNotification
object:self.view.window];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(embeddedVideoEnded:)
name:UIWindowDidBecomeHiddenNotification
object:self.view.window];
If, I find a fix for the second notification I will posted it.. :)
I wanted to run a instance method from my BPGameController class called "pauseGame" in my app delegate when my application enters background mode and when it resigns, and a instance method called "resumeGame" when the application becomes active again, I've tried a few different things but none have worked for me so far
In BPGameController's viewDidLoad method sign up for the notifications as follows:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(pauseGame)
name:UIApplicationDidEnterBackgroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(resumeGame)
name:UIApplicationDidBecomeActiveNotification object:nil];
When you are done remove yourself from observing.
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidBecomeActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil];
Currently I'm only calling one method when application will enter foreground. How do I call various methods in #selector?
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(displayHappyFace)
name:UIApplicationWillEnterForegroundNotification
object:nil];
Just create a separate function for all your other function.
[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(AllFunction)
name:UIApplicationWillEnterForegroundNotification
object:nil];
All functions.
-(void) AllFunction
{
[self displayHappyFace];
[self otherFunction];
}
Add another observer to UIApplicationWillEnterForegroundNotification if you wish to keep the methods' logic separate:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(displayHappyFace)
name:UIApplicationWillEnterForegroundNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(callOtherMethod)
name:UIApplicationWillEnterForegroundNotification
object:nil];
#selector supports only one method. Remember to remove self as the observer before releasing its memory, to avoid messages being passed to a nil object.
You can only put one selector there.
Best practice is to create a new method called handleNotificationName: for each notification.
Example:
- (void)handleUIApplicationWillEnterForegroundNotification:(NSNotification *)aUIApplicationWillEnterForegroundNotification { }
This makes it really easy to figure out where your app handles each notification and makes code maintenance easy.
Inside the handler method you can call whatever methods you need to. You can have conditional logic also based on state you have or based the userInfo dictionary of the Notification ( if it has one ).
Don't forget to remove your notification observer in you object's dealloc method (at least, if not somewhere else because you might not want to always receive the notification depending on the use case)
I'm adding a view controller as an observer for UIKeyboardWillShowNotification notification.
I have this code in my viewDidLoad:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardWillShow:)
name:UIKeyboardWillShowNotification
object:nil];
And in my dealloc:
[[NSNotificationCenter defaultCenter] removeObserver:self];
The observer is not being removed even though dealloc is called when the view controller is closed. So when I open it for the second time, NSNotificationCenter will attempt to notify the old object, which is released, and the app crashes.
I have seen several questions here on StackOverflow about this particular problem, but non of the answers works for me.
I've tried removing the observer in viewWillDisappear and viewDidDisappear but the same problem happens.
I'm using ARC.
Have you tried this exact chunk of code in viewWillDisappear?
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
[[NSNotificationCenter defaultCenter] removeObserver:self];
}
From your explanation I don't think the problem is with the removal of the observer.
Try to trigger the Observer from another viewcontroller. If it's not triggered you'll know the removal is successful and the problem occurs when you are adding the observer the second time.
Maybe try by specifying the parameter name that you have set before like this :
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
Looks like the observer is getting set multiple times. Is your controller inherited from a class which also registers for same notification? That could lead to controller instance getting registered as observer more than once. As a workaround try this, in your controller class where you add the observer,
// Remove as observer first
[[NSNotificationCenter defaultCenter] removeObserver:self];
name:UIKeyboardWillShowNotification
object:nil];
// Then add
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(keyboardWillShow:)
name:UIKeyboardWillShowNotification
object:nil];
This will ensure that the observer is getting added only once.
Hope that helps!
[[NSNotificationCenter defaultCenter] removeObserver:self name:#"name" object:nil];
it works fine with me
Say if I have several:
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(notificationReceived:)
name:NotificationA
object:self.player];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:#selector(notificationReceived:)
name:NotificationB
object:self.player];
The objects are all self.player but for different notifications, in the end I do:
[[NSNotificationCenter defaultCenter] removeObserver:self];
Is this fine or do I have to use the full method to remove observer for each notification? Currently I'm having issue when the view controller is unloaded but player is still playing in background.
Thanks
The docs say: "removeObserver: Removes all the entries specifying a given observer from the receiver’s dispatch table." So your method call is enough.