First of all Check This to understand what i am doing
I did not get my answer in above question & still waiting for it.
Now new porblem is that when i click on back button using following code, methods of last ViewController are still running. It will use memory & keep processing untill it gets response(that`s what i want to do but if user press back then i want to stop all methods)
[self.navigationController popViewControllerAnimated:YES];
How do i stop it?
You need to do [getTryAgainTask cancel] (assuming getTryAgainTask is of type NSURLSessionDownloadTask) before you pop this controller. The download task is asynchronous and runs irrespective of the controller (that fired it) being deallocated. This might cause retain loops, leading the app to eventually crash. The code as of now, will go into an infinite loop. A better solution would be to keep a tab on the number of retries (say 3 times) and then prompt the user about the problem, asking if he/she would like to try again.
Related
First of all I'd like to say sorry in case my question is dummy, I'm really new to iOS and what to understand how thing are going on. Imagine such a situation - user taps on home button and the app starts to collapse, but immediately after taping on home button user taped on some UI element. So, I'm wondering how the iOS will handle this? I tried to do some tests using breakpoints, but since it just test I can't be 100% sure. It seems that if the UI interaction event will happen before the system will call willResignActive then the event will be fully processed and if the system will call willResignActive first, then the even will be discarded and won't be handled at all. Is this correct, or I missed something? Thanks
First, why do you want to use this in your app? If a user presses a button exactly in this time, it's okay that the action is not handled.
The only thing you have to keep track of is that whenever the button gets pressed and let's say you store a file without a completion handler it could be that you present an alert which is saying that everything went well but you actually not saved the file because the user left the app in this time.
But since you're never doing critical actions without completion handlers, in my opinion, there's no need to make sure that this doesn't happen.
If I got you wrong, just comment!
I'm doing an alarm application with repeat interval. My problem is that even if the user clicks the local notification, returns to the app, and then goes back to the home screen of the phone the UILocalNotification stills fire every minute. I'm aware of [[UIApplication sharedApplication] cancelAllLocalNotifications]; and I put it in the my viewDidLoad method. Any advice how I can fix this?
Putting it in viewDidLoad is good for some circumstances just not yours. Think about when viewDidLoad is called:
Called after the controller's view is loaded into memory.
So in other words, the next time it gets called is after your little ARC friend deallocates it from memory. So, yes, eventually cancelAllLocalNotifications will get called again, just not when a user puts the app in the background and then returns it to foreground, because its still has a home in memory; it will be called next time that particular view gets loaded into the memory.
Additionally, that probably is not good logic, because that will happen for every user, even if they didn't want to cancel the repeats.
Ultimately, you will have to create additional logic to decipher which users have, say, hit 'snooze' or 'cancel' with whatever resource works for you and your project. Personally, I would guide you towards using a category based notification, that way you cancel it as needed, instead of 'just in case'. See here how to set those up.
I've come across a strange error while programming my iPhone application. Basically when I leave my application in the background and then access it after a long time (i.e. the entire night while I'm sleeping), the viewDidLoad method seems to be called again even though I did not exit the app (I only double tapped the Home button or I tapped the Home button once) but still left the app in the background. However, if I leave the app on for a short period of time (anytime between a few minutes to a few hours), the viewDidLoad method is not called again and everything is as it should be. After doing some research, I found that it is because the viewDidUnload method is called (after the OS finds that the app is suspended for a long time), which calls viewDidLoad again when we bring the app back up. I found this out through this link: view seems to reload itself but it doesn't seem that there's a way to prevent viewDidLoad from being called when the viewDidUnload is called. Is there any way to prevent this viewDidUnload method from being called again? The thing is I want my app to be running for a long time in the background (i.e. a few days in the background) to collect data. Or, is there no way around this? Any help would be appreciated. Thanks!
EDIT: I have realized that after iOS 5, viewDidUnload is deprecated but this phenomenon still occurs. Any ideas on how to fix it? Thanks!
If you want to do stuff in the background you should look into background tasks.
I'm slowly working on my first simple timer app, which is starting to slowly come to life. At the moment I've done no saving of data for when my app enters the background, for the moment whilst writing my app it is always staying loaded during my testing, even if its in the background for a small time. All this is being done on the simulator.
My problem is that I have a Table View Controller with an NSInteger index property
#property NSInteger index;
that I use to manage the slow iteration step by step over an NSArray over time, by calling a doWork method.
Initial setup of my TVC and this property is performed as the view is prepared for segue from another view. More work is done on this property and other properties whenever my app receives local notifications or upon observing UIApplicationWillEnterForegroundNotifications.
All accessing of this property I've added debug logging around and I'm just confused with what I'm seeing
PrepareForSegue
# 19:38:29:058 - calls a method doWork which increments my property from -1 to 0, and sets a local notification. Logs show self=0x10bb661f0
I press the home button to put my app in the background for ~10 secs
The local notification fires and I tap the banner to bring my app back to the focus
My TVC's awakeFromNib function sets up a notification observer
as follows
NSOperationQueue *mainQueue = [NSOperationQueue mainQueue];
[[NSNotificationCenter defaultCenter] addObserverForName:UIApplicationWillEnterForegroundNotification
object:nil
queue:mainQueue
usingBlock:^(NSNotification *note) {
[self doWork];
}];
This notification fires twice! (for some reason?) each time causing my doWork method to be called
# 19:38:45:832 - doWork immediately shows my property is now back to -1 not the 0 it was set to before being backgrounded, it is incremented again to 0. Also it shows self as different at self=0x10974bbd0, a value it remains at now whilst the app is foregrounded.
# 19:38:45:836 - doWork is called again from this 2nd notification call, my property is correctly now still 0 from the last call, it is incremented again to 1.
after that my app delegate also gets it's didReceiveLocalNotification method called, which will also end up calling the same doWork method via another block in a Notification Center observer setup the same as the one detailed above.
# 19:38:45:857 - doWork is called and again the property has gone from the 1 that was set, back to 0... and is again incremented back to 1.
I just can't understand what's going on. Most of the properties in my TVC are still presumably fine as the rest of my logic showing the TVC contents continues to work fine. Why is my NSInteger getting mangled so?
I thought perhaps there could be some issues with threading and the local notification handling occurring perhaps simultaneously, I hoped that adding the mainQueue would help with this, I'd previously got this set to nil. Sadly it didn't make any difference.
I wonder why self changes after being backgrounded for only a short amount of time. Naively I presumed that as everything seemed to be working on coming back to the foreground (the view still displayed, with all its data seemingly intact aside from this NSInteger property) that the self ptr and object would be the same. It's not too much to imagine that perhaps its been relocated by the OS somehow, but still this shouldn't have caused the property to change.
I'm using cocoa lumberjack for logging, and I've turned off ASYNC logging as follows
#define LOG_ASYNC_ENABLED NO
Which should at least mean that log calls block till they've logged. I could appreciate that if i did have some threading issues perhaps the logging order would be slightly in doubt. But for the initial corruption of the property described above after the app enters the background there is ~10 seconds from when I write 0 to the property, and later read -1 back out of it. This is clearly not a threading timing issue at that point.
Why am I notified about entering the foreground twice? If my properties were left where I set them it wouldn't matter much, but still strikes me as a little odd.
Is there a problem with my using self within this block, I've seen that sometimes you may want to use a weak self pointers for these blocks, but I've seen examples where self is used directly as well.
Any help on understanding and hopefully fixing this would be really appreciated. I'm a little stuck and can't see what I've done wrong!
Cheers
So the answer to my problem as figured out by Woofbeans and Phillip Mills is that my awakeFromNib was being called each time i entered this TVC, and also I was failing to removeObserver on these notifications causing the stale undisplayed TVCs to stay around indefinitely. I'd not realised this key part of my repro of the problem.
Go into the TVC, come out, go back in and then you would have a duplicate of alerts in the app being caused by the fact that the original TVC was still around, being held onto by the strong reference to self within my own blocks.
I'm going to refactor this doWork functionality into my model so that it can persist and be handled better, independently of whatever view happens to be being displayed.
I also changed my block code to use a weakself pointer within the block, to hopefully stop that block from causing any object to persist purely because of the block being left behind.
Cheers everyone!
I'm developing a small app on top of core data. At startup, I need to launch a maintenance task - fast but important -. To run this task, the app delegate must open a UIManagedDocument, and perform various checks on it. The app views must not start until the checks are completed. Because opening a UIMD is asynchronous, the app delegate isn't done when the first UIview tries to access the doc. The application then crashes due to a race condition because the app delegate and the view are trying to open the doc at the same time, while the doc state isn't yet finalised.
I'm using a storyboard, so segues are pretty much in control of the OS... Next time, I'll do it all manually..
What would be your recommendations ?
Note:
1)I can not perform the task when the app. goes into background state, because if it is brought back up again, avoiding inconsistent states between the underlying database and what's displayed in the view will be very tedious.
2)For the same reasons, performing the maintenance task during normal execution is not easily done.
3) All views access the UIMD via a singleton, according to the code proposed here
Setting a mutex lock in the UIView isn't my preferred route, because the screen remains black - no data -, while displaying the tab bars, until it is released by the app delegate.
Is there a way to have the app delegate wait for a signal before it hands the control over to the UIViews ? In this case, are there any gotchas ? I suspect this is probably not the recommended way to do, and iOS might kill the app if the delegate stays too long waiting for the maintenance task to complete. What would be "too long" in this case?
You could do it more elegant way. The first view the user will see must be some kind of SplashView - just an image with progress indicator. It should stay on top while your task is going on. It's not too important how you're showing this view. You can set it as the first in your storyboard or just create it manually in applicationDidFinishLaunching message.
Then in your task send a NSNotification when it's about to finish and in the observer in your AppDelegate just hide your SplashView and present your first view with valuable content.
You can even add some visual effects for transition between those views and your app will look really great! :)