I noticed some bizarre behavior in my iPad app: when the app transitions to the background, my active view controller receives viewWillAppear/viewDidAppear messages.
From my investigation, it seems this is happening because when my app moves to the background, my UISplitViewController for some reason first transitions its display mode to .PrimaryHidden and then immediately back to what it was before (.AllVisible).
Is this expected behavior? If so, why does UISplitViewController need to change its display mode (twice) when the app suspends, and is there a way to prevent it from doing so?
Edit: I just verified this behavior with a simple test app, but I'm no closer to understanding why it happens or how to prevent it.
Related
My iOS app returns back to rootViewController when kept in background for longer time.
To demonstrate I have the below picture
I navigate all the way to ViewControllerC and keeps the app in background, when I returns to the app say after 30 mins, the app shows rootViewController i.e. ViewControllerA.
I want it to remain on ViewControllerC as it stays in Whatsapp. I know that my app (idle apps) will be removed from the memory when system falls short in memory, so when I open the app it will take me back to the initial View controller specified. But then why this doesn't happen with whatsapp?
Apple provides a solution to this situation: UIViewController, along with the App Delegate, has methods permitting you to save and restore state. When the app goes into the background, the current configuration (what view controller's view is showing) is saved. That way, even when the app quits, when it relaunches it can get back to that configuration before it appears to the user. Thus, coming back from background-and-quit looks just like coming back from mere backgrounding.
For full details, see Apple's documentation. This is a good place to start:
https://developer.apple.com/library/ios/featuredarticles/ViewControllerPGforiPhoneOS/PreservingandRestoringState.html
When a foreground app gets backgrounded (e.g. Home button gets pressed), how can I change elements on the topmost view controller prior to when iOS takes a snapshot of it and starts the animation to show the next screen?
I ask because I'm writing an app requiring HIPAA compliance, and I am concerned that the snapshot that the OS takes in order to do this animation sometimes contains sensitive data which should not be visible even for a split second when the app gets foregrounded later.
I'm aware that view controllers have lifecycle methods such as viewWillDisappear which might be usable, but I have a lot of controllers and I'd rather just have something in my App Delegate to handle this (e.g. by adding an opaque full-screen UIImageView overlay) rather than having to write custom code for this in every last controller.
I tried putting overlay-generating code in applicationWillResignActive, and I've been digging with Apple's docs and Google, but it's not working. I suspect the screenshot gets taken before the app has a chance to update the screen.
Thanks!
Not sure about HIPAA's requirements about backgrounding and possibly leaving the user logged in for someone else to resume, but the safest sounds like it would be to add a key UIApplicationExitsOnSuspend with a boolean value of YES to info.plist.
That will prevent the app from backgrounding entirely, and restarts it (possibly triggering a login procedure) every time you go back to it.
Most (if not all) mobile banking applications I've tested do this for safety reasons.
I believe the answer is to not concern oneself with changing what's on the screen before the backgrounding animation begins, but to simply modify what's displayed on the screen once the app enters the background (i.e. inside of applicationDidEnterBackground: in your App Delegate.) This solved my problem.
My UIImageView overlay idea worked here, although I decided just to pop to the root view controller instead. Simpler that way. My root view doesn't have any sensitive info.
Here's what it looks like:
-(void)applicationDidEnterBackground:(UIApplication *)application {
UINavigationController *navigationController =
(UINavigationController *)self.window.rootViewController;
[navigationController popToRootViewControllerAnimated:NO];
...
}
During an active VOIP call, my app is put into the background when an incoming cellular call is received and answered. If, while on the cellular call, I bring my app back to the foreground the app view appears but is unresponsive. The "Touch to return to call" banner appears at the top of the view in green but the app view appears as if there is a darker transparent window overlaid on top of it preventing the view from receiving input. If I put my app into the background, bring another app to the foreground and then bring my app back to the foreground everything works as expected so the problem seems to be specific to active cell calls and/or the green banner only? In Settings->Notifications->Phone I tried turning Notification Center OFF and Alert Style NONE in the hopes of removing the banner to see if the problem still exists but these settings do not effect that banner. In addtion to the App window appearing to have a transparent window overlaid on it, if I touch the window I'm able to drag the entire app window (or view) in all directions (up down side to side) and it has a bounce effect (like tableview vertical scroll) when I release it.
If I dont know the problem I cannot fix it (:
Thanks..
Are you sure there's no view being added on top your view which might be intercepting all your events? My second guess would've been that your app received a memory warning and unloaded a bunch of views. However, that's not very likely since you still see all the views.
I don't know what you really mean to "bring your app back to the foreground",but I can tell you for sure that you cannot call in the same thread the UI and the incoming call, so for situations like this when you want to render some view during a call you can try something like this:
public void InvokeGUIThread(Action action)
{
Dispatcher.Invoke(action);
}
For example if you want to set a text in a textblock do something like this:
InvokeGUIThread(() =>
{
textBlockSome.Text = e.Item.ToString();
});
I just set the 'Application does not run in background' parameter of my ios app to NO and I added the relevant refreshes in applicationDidBecomeActive: in my application delegate then it works pretty well. But when I switch back to my app, the splash screen still appear during one second. How to remove it and display directly the app ?
I though it was impossible, but it remembered me this topic : Prevent Splash Screen from showing after returning from background
It seems to include an answer to your question...
Also, don't forget to try on the device, sometimes the simulator does weird things.
I'm currently working on a change request for our iPad app that requires that I handle the resuming of the app in two different ways depending on whether the app returned from multitasking (the user was active in another app or on the homescreen and came back to the app) and standby (the iPad was switched to standby either through the standby button on top or by closing the Smart Cover)
In both cases the following methods are called in my AppDelegate:
applicationWillResignActive followed by applicationDidEnterBackground when I hit the homebutton to get tot he home screen or close the Smart Cover
applicationWillEnterForeground and applicationDidBecomeActive when I come back.
As the same methods are called I am a bit lost on how to detect where I come from on resume. All four methods have a single parameter passing in the UIApplication. I looked at its interface, but didn't find any useful clues.
Is there a way to differentiate between resuming from multitasking or standby?
There is no public api method to define why application did become active