Long story short, I'm trying to change my iOS app's rootViewController on applicationWillEnterForeground:, like so:
- (void)applicationWillEnterForeground:(UIApplication *)application
{
MyViewController *controller = [[MyViewController alloc] init];
self.window.rootViewController = controller;
}
However, when iOS performs the "zoom in" animation that is performed when an app is moved from the background to the foreground, it still shows the previous rootViewController's view. Then, as soon as the animation is complete, the app blasts the new rootViewController's view onto the screen.
One way to solve this is to simply move that code to - (void)applicationDidEnterBackground:, but the problem with this solution is that, in my app, there is no way to tell if a new rootViewController will be assigned until - (void)applicationWillEnterForeground:(UIApplication *)application (it is based on time passed since leaving the app).
How can I force the app to redraw before iOS performs the animation taking the app from the background to the foreground?
I believe this is not possible. The screen that iOS shows of your app when it comes into the foreground is actually a screenshot the system took when the app went into the background. There is no way to manipulate or replace that image at the time the app comes back into the foreground.
This behavior is partly documented in the Moving to the Background section of the iOS Application Programming Guide:
Apps can use their applicationDidEnterBackground: method to prepare for moving to the background state. When moving to the background, all apps should do the following:
Prepare to have their picture taken. When the applicationDidEnterBackground: method returns, the system takes a picture of your app’s user interface and uses the resulting image for transition animations. If any views in your interface contain sensitive information, you should hide or modify those views before the applicationDidEnterBackground: method returns.
Apple does not explicitly document that you cannot modify or replace this screenshot at a later time but neither do they say the opposite anywhere I know of.
Related
I am trying to set time for the launchscreen.xib to make it last longer, for example 5 sec,since by default it disappears too quick i searched the web but found nothing useful, can it be done ?
Thanks
The apple documentation mentions this:
A launch file or image provides a simple placeholder image that iOS displays when your app starts up. The placeholder image gives users the impression that your app is fast and responsive because it appears instantly and is quickly replaced by the first screen of your app.
So essentially the launch screen cannot be made last longer because its only displayed when the app is starting up.
Still if you want you can
create a custom UIView with the launch image
make it the Initial View Controller by dropping the arrow in storyboard to your custom UIView
present your main View Controller on top of the launch image view after x seconds using dispatch_after
You can add this in your app delegate:
float delay =5.0;
- (void)applicationDidFinishLaunching:(UIApplication *)application {
[NSThread sleepForTimeInterval:delay];
}
If you use a viewController, you can present it again in - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
making it the UIWindow's rootViewController, or presenting it modally from your application in the same method. This way, you can customize its dismissal. You can also add some animation to this viewController
So it may be another viewController than your launchScreen.
What exactly happens with an app when the user presses the home button? Does iOS make a snapshot of current app's state?
If I'm right, how to "slip in" another snapshot? I need it for showing the main iOS screen after user presses home button twice.
In order to achieve that, you could add a subview (i.e. ImageView with an image of your main screen) to your window in - (void)applicationDidEnterBackground:(UIApplication *)application.
When coming back (in - (void)applicationWillEnterForeground:(UIApplication *)application) you have to remove the subview.
However, Apple recommends to always show the latest state of the app (best user experience).
Example of AppDelegate implementation:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
/* other code */
self.overlayView = [[UIImageView alloc] initWithFrame:self.window.bounds];
self.overlayView.image = [UIImage imageNamed:#"mainscreen_screenshot.png"];
/* other code */
}
- (void)applicationDidEnterBackground:(UIApplication *)application
{
[self.window addSubview:self.overlayView];
}
- (void)applicationWillEnterForeground:(UIApplication *)application
{
[self.overlayView removeFromSuperview];
}
iOS takes screenshot before your application goes to background.
I got it from Apple's official documentation.
Remove sensitive information from views before moving to the background: When an app transitions to the background, the system takes a snapshot of the app’s main window, which it then presents briefly when transitioning your app back to the foreground. Before returning from your applicationDidEnterBackground: method, you should hide or obscure passwords and other sensitive personal information that might be captured as part of the snapshot.
So, Here We can hide our "sensitive personal information" and the system takes a snapshot of the app’s main window and we are not able to change its feature.
# sensitive personal information
Set a blurry screen overlay before the app goes in the background and once the app becomes active remove this overlay (check #cweinberger's answer).
If it is iOS 7 or later you can use the function ignoreSnapshotOnNextApplicationLaunch
Also, allowScreenShot flag can be explored in Restrictions Payload.
For deeply read about it Then this is the best documentation.
My app checks the GPS while my app is not the active app and I use AVAudioplayer too in background.
It works fine and stays in the background doing its thing, but ios7 displays this red top banner with my app name flashing on it when it is not the active app.
How can I disable this banner, it is annoying to use other apps that are squished down 1 line?
I know this can be done as I have other GPS based background apps that don't display this flashing banner.
EDIT - So we found the answer quickly but the solution evades me:
If I stop OpenEars pocketsphinxController from listening with a button that calls this method while the program is active, the banner disappears when the app loses focus:
-(void) mystopListening{
NSLog(#"Tried to stop listening");
[pocketsphinxController stopListening];
}
BUT if I call the same method from my app delegate with (I had to import my view controller.h file in my app delegate.h and add -(void) nystopListening; in my view controller.h to make the below execute properly):
- (void)applicationWillResignActive:(UIApplication *)application{
myViewController * vc = [[myViewController alloc]init];
[vc mystopListening];
}
The banner persists! It is a little like ios7 has decided I am a recording culprit before I even have a chance to turn it off. OR, am I even turning it off?
How do I do this effectively and in what event?
EDIT - So it turns out I am not really turning pocketsphinxController off when 'mystopListening' is called from the app delegate. I know this because it DOES log the 'Tried to stop listening' when called from app delegate but the pocketsphinxController does not respond with its 'pocketsphinxDidStopListening' method. PocketsphinxController does call its 'pocketsphinxDidStopListening' method when I call 'mystopListening' from a button while the app is active.
Why won't the pocketsphinxController respond when called from from the app delegate, I must be doing it wrong?
Thanks,Carmen
Turns out I was not really calling the original pockectsphinxcontroller instance from my app delegate.
As a workaround to the problem I did this:
My app always has a timer running, so in my app delegate where I get notice of when app goes to inactive and comes back active, I just set global flags so my timer can know app active status. Then my timer just uses pockecsphinxcontroller methods to stop and start listening and voila, the banner is no more while app not active.
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];
...
}
In my application, When the application goes to background I am calling a Passcode page (Passcode Page which does authentication).
My requirement is when the user launch the app from the foreground he will see the passcode page. If he enters the correct passcode then only he can see the rest pages.
In delegate.m file
- (void)applicationDidEnterBackground:(UIApplication *)application
{
PasscodeViewController *passcodeController = [[PasscodeViewController alloc] initWithNibName:#"PasscodeViewController" bundle:nil];
[navController pushViewController:passcodeController animated:YES];
}
When I am launching the application from the background then It is showing me the previous page( from which page I came to background ) for a fraction of second and after that Passcode page comes.
But I want to hide my confidential information from others (who doesn't know the passcode) that are shown in the previous page.
It is correctly working in Simulator but in Device it is not working properly.
Can you please guide me in that ?
OR
Is it the normal behavior of the iOS device ? What ever the page transition it will do, it will perform while the application is running in foreground.
I am not sure about that. Please tell me where I went wrong.
Thank you.
Every app I've used with a similar feature has operated as you describe, with the fractional-second flash before the lock view appears.
I think it's a matter of when UIKit thinks it needs to re-render... We had a similar case with a splash screen, but using applicationDidEnterBackground for adding the splash helped.
My idea is to avoid the animating, using
[navController pushViewController:passcodeController animated:NO];
Whenever your app goes background add a UIView with white background.
Whenever your app comes up push your PasscodeViewController view on top
Please add observers for UIApplicationDidEnterBackgroundNotification and UIApplicationWillEnterForegroundNotification to do the above functionality
Also be sure to remove the Observers when your view disappears
When user enters correct passcode remove the UIView.
Try applicationWillResignActive:
- (void)applicationWillResignActive:(UIApplication *)application
{
PasscodeViewController* passcodeController = [[PasscodeViewController alloc] initWithNibName:#"PasscodeViewController" bundle:nil];
[navController pushViewController:passcodeController animated:YES];
}
When Application goes to background push the passcode viewcontroller to navigationcontroller in the delegate applicationDidEnterBackground because there will be that fractional flash almost all time u can have the passcodecontroller pushed before entering background.