I am creating a simple application which perform some task on main thread. I am printing process in NSLog so I can understand that my process is running or not.
Now when I press home button without starting the process (Process will be start when I tap on a button) application enters in background and my both of methods applicationDidEnterBackground & applicationWillResignActive are being called.
But when I first tap on my button and process starts on main thread after that if I press home button none of these two method being called. So my application can't know that app entered in background or not.
Even after that when I again active the app it shows me a black screen with status bar only.
Why this is happening?
Why app not entering in background?
Why apple's methods not being called?
Is there a way to solve it?
UPDATE
Here is my appdelegate class code
- (void)applicationWillResignActive:(UIApplication *)application
{
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
}
All methods have no implementation.
Thanks in advance.
I am creating a simple application which perform some task on main thread.
Don't perform long-running operations on the main thread.
The delegate callbacks happen on the main thread. If the main thread is busy, then the callbacks won't happen until you return to the "run loop".
When foregrounding your app, the OS actually displays a screenshot if available, falling back to the launch image (Default.png). The screenshot is taken after -applicationDidEnterBackground: returns, which allows you to customize what gets saved (you might want to do this for security reasons, or to hide UI elements which might not make sense to show when relaunching e.g. a countdown timer).
The black screen is probably because your app has no launch image. If your app takes more than about 10 seconds to enter the background (and it does, since the main thread is blocked), it gets killed. Except the debugger is attached and catches SIGKILL, so it's easy to miss unless you're watching Xcode.
there are some cases
if UIApplicationExitsOnSuspend key set to true in your app's Info.plist, the applicationWillResignActive method is not called when the user hits the home button. and may b some thing other. check keys here Apple keys and see if something new you added to plist. and there is no other case that you say your delegate method not calling. it may also some time due to project in appropriate behavior. try cleaning your project and rebuild.
this is going to sound strange but for those it helps. I had the same issue and cleaned my project and then it started working again.
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.
In my app from applicationDidEnterBackground i want to ask the application for more time to
create a UIWebView and load request with UIBackgroundTaskIdentifier, then in the delegate
method of UIWebView (webViewDidFinishLoad) i want to do a stuff there and show an alert or
notification while the
application is still reining in the background .
so how i can do that?.
Apple's documentation for UIApplication class for beginBackgroundTaskWithExpirationHandler: method says:
You can call this method at any point in your application’s execution.
You may also call this method multiple times to mark the beginning of
several background tasks that run in parallel. However, each task must
be ended separately. You identify a given task using the value
returned by this method.
This method can be safely called on a non-main thread.
So, once web view finish loading in background you can trigger another operation from webViewDidFinishLoad to show alert.
When you receive applicationDidEneterBackground your app is already effectively in the background. At that moment all your networking should be closed and you really shouldn't try to show any alerts or notifications.
I have an NSOperation running not in the main thread. It is spawned from a UITableViewController. When the operation is complete, I'd like to reload the tableview since some data has changed. I've set a delegate for the background to notify on completion. When done, I call a wrapper around reloadData specifically on the main thread using performSelectorOnMainThread.
For the most part, this works well, however, there is a non-0 chance that the original (edit)tableViewController (/edit) gets released and I get zombie calls.
So the question is in 2 parts:
Is it possible to have a delegate from the background thread without retaining the object?
Is this just a bad design? Should I be using NSNotifications instead? Would that be the preferred method of notifying in this case?
Thanks in advance.
A delegate should be retained if there is a possibility that it might be released before any operation on the delegate is invoked. You can set up a state in tableViewController to handle the case when the delegate callback is invoked and the tableViewController is not to be used (Basically make the callbacks act as no-op). Once your operation is done, just release the delegate object.
It is not a bad design but you just need to handle these conditions.
I have a Iphone app with 2 threads. One is listening to the server, and the other is doing UIKit, OpenGl stuff.
I need to run a method that updates a view from the secondary thread thats listening to a server on the main thread that handles the views so I used
performSelectorOnMainThread:#selector"createGuessingView" withObject:nil waitUntilDone:YES
but for some reason, the method never gets executed. Putting a breakpoint or a printf at the beginning of the method shows that its never invoked. Im really stumped here. Ive used performselectoronmainthread in the same program to update text fields and it worked flawlessly.
edit:
Figured it out :)
The problem was that the object that I was using performSelectorOnMainThread was set by this thread before the object was initialized (even allocated) in the main thread. Therefore, the reference was pointing to null, and the selector was not getting recognized.
Thanks for the help
Shouldn't that be:
#selector(createGuessingView)
with no quotes.
--
EDIT (in response to comment)
What the signature for your method? If it's:
- (void)createGuessingView:(id)something
then you should remember the colon, as in #selector(createGuessingView:)