I've read a lot of suggestions for the right place to call .removeObserver for NSNotificationCenter since viewDidUnload is not an option.
I was just wondering if the new deinit() in Swift would be a good choice?
-nick
It really depends on the role of the class where you subscribe to NSNotificationCenter notifications. If you are subscribing in:
UIView
Then you should unsubscribe as soon as view gets invisible to the user. To save CPU cycles and not consume resources while user does not see the view.
UIViewController
Here it also depends on kind of action that you are going to perform in response to notification. If it is just a UI adjustment that you should unsubscribe as soon as view controller disappears from the screen.
You App Service layer
Here it is OK to have .removeObserver inside deinit(). however even here I tend to suggest you to be more explicit about when you subscribe and unsubscribe from NSNotificationCenternotifications and put them in start and stop methods of your service.
If you were previously calling removeObserver in viewDidUnload/dealloc/deinit, then starting with iOS 9.0 and macOS 10.11, you don't need to call it anymore:
If your app targets iOS 9.0 and later or macOS 10.11 and later, you don't need to unregister an observer in its dealloc method.
source: https://developer.apple.com/documentation/foundation/notificationcenter/1413994-removeobserver
I want to call a method in background to check for new notifications and mentions for Facebook and Twitter. How can I do this ? Currently I am calling methods on view will appear of main view only. If any notifications will be there then I have to show badge count also.Shall I use NSThread For this purpose . I am not very much aware about NSThreads.
Please help
Thanks..
You can use NSOperationQueue for your requirment. Which executes set of NSOperation objects concurrently. And Implement a delegate method to update badge.
http://developer.apple.com/library/ios/#documentation/General/Conceptual/ConcurrencyProgrammingGuide/OperationObjects/OperationObjects.html#//apple_ref/doc/uid/TP40008091-CH101-SW1
My app delegate method applicationDidBecomeActive: is getting called twice for the first time launch of the application. I have some portion of code which I want to execute only once & that I have put into applicationDidBecomeActive:
What should I do?
I got the issue. I am using Location Services. When launching for the first time after I tap on "OK" on the location services alert, my applicationDidBecomeActive gets called one more time which is the normal iOS behavior.
If you want to call your code only once when app becomes active, try calling it from two methods.
didFinishLaunchingWithOptions
applicationWillEnterForeground
instead of calling it only from applicationDidBecomeActive.
This is because of location or push notification alert.
After the native location/push notification has been dismissed, applicationDidBecomeActive will be called.
I don't know if this will help, but I just had the same issue with a totally simple app that doesn't use Location Services, and I found out it's an illusion. Look at the logging messages I got:
2012-12-22 10:47:45.329 Bizarro[10416:907] start applicationDidBecomeActive:
2012-12-22 10:47:45.333 Bizarro[10416:907] end applicationDidBecomeActive:
2012-12-22 10:47:45.329 Bizarro[10416:907] start applicationDidBecomeActive:
2012-12-22 10:47:45.333 Bizarro[10416:907] end applicationDidBecomeActive:
Look closely. Look at the times. The first and third messages have the same time. The second and fourth messages have the same time. They are the same messages! It's an Xcode bug; it has nothing to do with my code. Xcode is reporting the same log messages twice.
In my case, I was able to prevent this by turning off all Behaviors for Running -> Generates Output.
What about:
Increment on applicationDidBecomeActive
Decrement on callback events of permissions requests or other alerts that trigger another applicationDidBecomeActive when closed.
With Xcode 6 there's a new reason this can happen: when you launch an app in a resizable simulator, applicationDidBecomeActive: will get called twice.
It launches the app with the default size class, and then applies the size you were last using—even if you were using the defaults. Any time a change in size class is applied, applicationDidBecomeActive: gets called.
When app launches first time
it calls sequentially,
didFinishLaunchingWithOptions
applicationDidBecomeActive (Twice)
When we open the Control Center it calls only,
applicationDidBecomeActive
When app come from background to foreground it calls sequentially
applicationWillEnterForeground
applicationDidBecomeActive
I'm currently seeing double notifications.
It's happening because my AppDelegate's init code is being called twice.
It's being called once when the main() does [[NSBundle mainBundle] loadNibNamed:#"MainMenu" owner:application topLevelObjects:&tl] (ie, when the .XIB file is loaded), becaues the .XIB file is setting up FirstResponder to my custom AppDelegate, and then it's being called again when main() calls [[myAppDelegate alloc] init].
The init code is what does the addObserver calls, so two observers are being set up for each notification I care about, which is why my notifications get called twice.
I'm a newbie OS X programmer, so I'm not yet sure of the best way to resolve these two, but wanted to post it here in case it's of help to others, another place to look.
Have you possibly created an instance of your class in Interface Builder AND in your AppDelegate code, perhaps?
If you have code you want called only once when the app starts up, then use
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
instead.
Otherwise, applicationDidBecomeActive will be called whenever your app becomes active again, so that doesn't just mean twice as in your case, but every time the user switches back to your app after switching to another.
If you use RxSwift, then you can just throttle the application event, so it doesn't call twice in the same second:
NotificationCenter.default.rx.notification(Notification.Name.UIApplicationDidBecomeActive)
.throttle(1, scheduler: MainScheduler.instance)
.subscribe { (event) in
self.appEnteredFromBackground()
}.disposed(by: disposeBag)
private func appEnteredFromBackground() {
Analytics.trackPageView(withScreen: .home)
dataStore.checkIfAllowingRides()
}
I put this code in my actual view controller where the logic is supposed to happen on ApplicationDidBecomeActive.
I just check at top of applicationDidBecomeActive: if the request was really sent (I made a function for this, checking status), if so I return already.
The second time in applicationDidBecomeActive:, the function reads the status as Deny or Allowed, because this is after the User answered the Alert.
I setup a network call in appdelegator class to get some infomation back, and I want to show it in the frist UIView. How to pass the data to that UIView?
I mean the UIView may be visible or may be destroyed and replaced by other one, if it was visible, how to pass that value to it?
is there any publish/subscribe events mechanism in iphone sdk?
You can do this a few different ways, including using key-value observing or NSNotifications.
The basic idea is that when you load your UIView, you want to register it as an observer of a key path/posted notification of the app delegate. When you deallocate your view, you should unregister it as an observer.
I am developing an iPhone application with multiviews (Nav controller), but i like to receive an event if user touches in any view of the view. I understand it can be done by subclassing application delegate? If that's true how can i do it? My requirement is, i like to receive an event as soon as user touches any where in any view within my application.
Thanks for your help and time.
Your reference to subclassing UIApplication will work. Read down through the comments and it covers a somewhat quirky IMO way to implement it (by having the AppDelegate be a subclass of UIApplication). Myself, I would create a separate class to be the UIApplication subclass, rather than having the app delegate do both jobs, but I see the merit of either way.
That said, this is a very large and unusual stick and may suggest a design failure. What problem are you solving with this?
A way to do it is to use a Singleton class (which acts as an observer/mediator), which the application is an example of, in which you have viewControllers subscribe to when they are intersted in the touch events of a certain view. When the touch occurs the Singleton class is informed of the event as a result it informs all subscribers to the event of the event.
Here is an example
#interface MyEventClass
{
-(void)TouchEventDidOccur;
-(void)subscribeToTouchEvent:(id)delegate selector(selector):sel
}
Above is the singleton class
now this is an example of what the view touchesBegan method might look like
-(void)touchesBegan...
{
[[MyEventClass sharedInstance] TouchEventDidOccur];
}
and how one would subscribe to the event
[[MyEventClass sharedInstance] subscribeToTouchEvent:self selector:#selector(receiveTouchEvent:)]
hope this helps
What's wrong with using notifications? If you have disconnected classes across your application, it's trivial to have them listen for a particular notification, then have your views or view controllers post that notification when a touch event happens. All of the observers will take action on the notification.