I am using the UIApplicationDidBecomeActiveNotification to refresh my tableview when the app becomes active. My problem is that in my ViewWillAppear, I am also calling a method to refresh this table's data.
This is causing the table to be refreshed twice upon application launch. How can I get one of them not to fire when the app is initially launched? Refreshing the table has some intensive processing of network and local data.. so I would really like o only perform this action once.
Thanks.
You need to use UIApplicationWillEnterForegroundNotification instead of UIApplicationDidBecomeActiveNotification.
The latter is posted every time your app becomes active (initial launch, back to app after call/sms interruption, etc.). But the former is posted only in case of wake up from background. Note that in this case viewWillAppear is not called (as it should seems to be at the first sight).
One way to do it would be with a flag, that you can set up in didFinishLaunching, since that is only executed once per launch.
Related
If I stop using my app for a long time then go back to it, it seems like the viewDidLoad method is being called again, even though I never "exited" the app (by pressing the home key twice and tapping the X) nor did I reboot the iPhone. If I just go to the home screen and then open the app again after a short time this does not happen. What is going on?
This has to do with the way that the operating system manages memory and how it deals with having many different apps open at one time. In a short summary, if your app is in the background for a long period of time, eventually, the OS will decide that it is inactive, and the memory associated with its view will be marked for reuse somewhere else where it is more needed. This is the viewDidUnload method in your view controller. Any time the viewDidUnload method is called, the viewDidLoad method will be called again so that you get a chance to reload your view before the user sees it.
Edit:
You cannot rely on this phenomenon happening every x minutes. It will only happen as the OS requires more memory for active apps. If you want to make sure the user always gets updated information when he or she resumes usage of your app, use NSNotificationCenter and register for the UIApplicationDidBecomeActive notification.
You can try to monitor the memory waring. Most of situation like this is memory warning get trigger and viewDidUnload get called after that if the view is not the top most. So when you back to that view, viewDidLoad will get called again.
You can try to override this method in UIViewController and see if memory warning get called. It maybe triggered by some other component in your application.
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
}
I use UIApplicationDidBecomeActiveNotification/UIApplicationWillResignActiveNotification pair to compute app running time. in callback of UIApplicationDidBecomeActiveNotification, I record the startTime, and in callback of UIApplicationWillResignActiveNotification, I record endTime.
in most case, I find the running time is correct. but there are some special case in server's log, I find the running time is strange. like the end time is less than start time, or the end time is much more than the start time. so I suspect the UIApplicationDidBecomeActiveNotification is not called in some times. if some one meet such kind of case, and give me some suggestion.
If you are listening for UIApplicationDidBecomeActiveNotification in a view controller, then viewDidLoad is not called until after UIApplicationDidBecomeActiveNotification is posted. So if you register for the notification in viewDidLoad, you'll miss the first notification, which happened before the view gets loaded. So every time your application launches, you'll miss one such notification. All subsequent notifications will be caught though, including returning from background etc.
UIApplicationDidBecomeActiveNotification will be called everytime your application is coming from background to forgnound.means everytime your application is becoming active from a nonactive state.I think that is the reason for the changing time.
I'm doing an app that uses a TabBarController and each Tab uses its own navigation controller.
The app has dynamic content and I use viewDidDisappear viewDidAppear methods to create or destroy the objects that I need each time I enter or exit into the ViewController.
My problem is when I start to sail very fast and I don't give time to load the Threads that I use for uploading content such as XML peta app or destroy objects when I leave the ViewController.
How I could control the tabs of the navigationbar or tabbarviewcontroller for not respond until the viewcontroller has loaded all contents?
Excuse me if I'm not well expressed. Thanks!
No matter you use synchronous request or asynchronous request, just show an UIAlertView while loading the data. This will both serve as a notification to the user that something is being loaded, and the it will block the interactions with all the other views on the screen.
As others have suggested in comments, I believe that what you want to do is rearrange the order in which things are triggered. Perhaps something like this:
On viewWillAppear:, clear (or disable or whatever is appropriate) your objects that are no longer valid and begin the load-new-content thread. Perhaps display a UIActivityIndicator or similar.
On viewWillDisappear:, tell the load-new-content thread that it can stop, its results are no longer needed. If you put up an activity indicator, take it down.
At the end of the load-new-content thread, take down any activity indicator, update the UI with the new contents and activate.
I don't really see any way around this -- if the UI is not valid until the new content is loaded, then you have to wait for it.
Another solution might be to cache the contents from the previous fetch, and always display those on viewDidLoad. Then, at the end of your new-content-thread, cache the new contents, and update the UI.
I'm trying to get my views to update when the user returns to the app while it is running in the background. My problem is this, I call the method that updates the view and a couple of UILabels but they dont update. The strange thing is, is that I have an NSLog in the method to ensure it is being fired. So I load the app, I hit the home button to return to the home screen, I open the app, I DO get an Log reading that the method I need fired IS indeed fired but the view sint updated. Help. Please.
Use applicationDidBecomeActive for this purpose.
Template implementation has the following comment:
Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
I have an app (a game) which saves data: game state, high scores, achievements, etc. Currently the app delegate does this on applicationWillTerminate:. After playing around with iPhone 4 for a bit, it seems that applications pretty much never terminate: they just run in the background forever, unless the user goes out of their way to quit them, or restart the phone.
So my question is, should I find another place to save my data, and if so, when?
To minimize the amount of time spent in the delegate method call, you should find a place that makes sense to save during the game (level completion, checkpoints, etc). You can also add a new delegate method to your application delegate which will be called when your application transitions to the background where you can duplicate some of the things you may have done previously in applicationWillTerminate:. The new delegate method to implement is -applicationDidEnterBackground:.
You will also receive a notification that the user switched back to your app as applicationWillEnterForeground:.
you can do so in the views diddisappear delegate method
-(void)viewDidDisappear:(BOOL)animated
{
//CODE FOR SAVING
}
There are 2 App delegate methods you can use
applicationDidResignActive: //pausing the app, used when a msg comes up. if multitasking this wont help
applicationDidEnterBackground: // called in iOS 4 for when the app is in the background
you can see when it loads into the foreground using
applicationWillEnterForeground:
check out the reference for more info
You should save in applicationDidEnterBackground. Make sure to wrap your saving code with – beginBackgroundTaskWithExpirationHandler: and endBackgroundTask, since without that, you have less than a second (or something like that) before execution suspends.