View added in applicationDidEnterBackground not visible until app returns from background

Question

I add an imageView to my app's main window in applicationDidEnterBackground:

- (void)applicationDidEnterBackground:(UIApplication *)application
{
        UIImageView *splash = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"splashimage.png"]];
        splash.frame = self.window.bounds;
        [self.window addSubview:splash];
}

I expect that when I put the app into the background by pressing the device's home button, then viewing the task manager by double tapping the home button, I will see the splashimage.png displayed. But it seems that the screenshot that is taken when the app goes into the background does not include this overlay imageView. I thought that it would, since I added the imageView with no animation.

Why might this might be happening?

UPDATE: Even if I hide my window in applicationDidEnterBackground, I can still see the full window, unhidden, in the task manager after the app is put into the background state. The window only becomes hidden a moment after the app returns from the background, when I press the home button.

- (void)applicationDidEnterBackground:(UIApplication *)application
{
        //this does not work either!
        self.window.hidden = YES;
}

UPDATE: I do understand, by the way, that applicationDidEnterBackground has 5 seconds to complete. I am now testing this with only

self.window.hidden = YES;

in applicationDidEnterBackground and nothing in applicationWillResignActive, and the window still is not hidden when the app goes into the background; only when it returns to the foreground. So this is telling me that there must be something else, somewhere in my app, that is not allowing this to happen in applicationDidEnterBackground. By the way, if I move the

self.window.hidden = YES;

to applicationWillResignActive, the window IS hidden when the app goes into the background. But I am trying to figure out what will inhibit an app from completing this single, simple, non-animated task in applicationDidEnterBackground. Any thoughts appreciated.

UPDATE: This particular issue has something to do with using a BannerViewController (iAd). I am using it in a UITabBarController. Not sure yet what exactly the issue is or if it is also related to its use within UITabBarController.

UPDATE: I think the issue is not related to the UITabBarController, but in general the BannerViewController (iAd). Now to understand why...

UPDATE: This line in BannerViewController.m is causing the issue:

[self.view addSubview:bannerView]

in this method:

- (void)viewDidLayoutSubviews
{
    CGRect contentFrame = self.view.bounds, bannerFrame = CGRectZero;
    ADBannerView *bannerView = [BannerViewManager sharedInstance].bannerView;
#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0
    NSString *contentSizeIdentifier;
    // If configured to support iOS <6.0, then we need to set the currentContentSizeIdentifier in order to resize the banner properly.
    // This continues to work on iOS 6.0, so we won't need to do anything further to resize the banner.
    if (contentFrame.size.width < contentFrame.size.height) {
        contentSizeIdentifier = ADBannerContentSizeIdentifierPortrait;
    } else {
        contentSizeIdentifier = ADBannerContentSizeIdentifierLandscape;
    }
    bannerFrame.size = [ADBannerView sizeFromBannerContentSizeIdentifier:contentSizeIdentifier];
#else
    // If configured to support iOS >= 6.0 only, then we want to avoid currentContentSizeIdentifier as it is deprecated.
    // Fortunately all we need to do is ask the banner for a size that fits into the layout area we are using.
    // At this point in this method contentFrame=self.view.bounds, so we'll use that size for the layout.
    bannerFrame.size = [_bannerView sizeThatFits:contentFrame.size];
#endif

    if (bannerView.bannerLoaded) {
        contentFrame.size.height -= bannerFrame.size.height;
        bannerFrame.origin.y = contentFrame.size.height;
    } else {
        bannerFrame.origin.y = contentFrame.size.height;
    }
    _contentController.view.frame = contentFrame;
    // We only want to modify the banner view itself if this view controller is actually visible to the user.
    // This prevents us from modifying it while it is being displayed elsewhere.
    if (self.isViewLoaded && (self.view.window != nil)) {
        [self.view addSubview:bannerView];
        bannerView.frame = bannerFrame;
#if __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_6_0
        bannerView.currentContentSizeIdentifier = contentSizeIdentifier;
#endif
    }
}

Not exactly sure why or what, if anything can be done to fix it if I still want to use BannerViewController.

UPDATE: from to the accepted answer below, here is what solved this problem for me (bannerVC is a reference to the BannerViewController).

- (void)applicationWillResignActive:(UIApplication *)application {

    [bannerVC.view snapshotViewAfterScreenUpdates:YES];
}

UPDATE: I realize that this code really should be in applicationDidEnterBackground. But, it seems with AdBannerView that there is no way to stop the animations in time so that this can happen. So for now, in my understanding, applicationWillResignActive is all that is left, but it leaves the user with a 'less-than' experience. I would appreciate any suggestions on how to stop the AdBannerView animations so that the snapshot can be shown in applicationDidEnterBackground and not only when returning from the background.

UPDATE: To replicate the issue:

1. Download iAdSuite
2. Open TabbedBanner example.
3. Add the code below to AppDelegate:
4. Run the app. (frames are messed up because it hasn't been updated but this example will still show the problem)
5. Tap the home button once to put the app into the background.
6. Double-tap the home button to see the app in the task manager.

If you have left the code in applicationWillResignActive commented and the code in applicationDidEnterBackground uncommented, you will not see a blue splash screen in the task manager. But if you have commented the code in applicationDidEnterBackground and uncomment the code in applicationWillResignActive, you should see the blue splash screen in the task manager. This is not desirable however. The issue is how to display the splash screen in the applicationDidEnterBackground method.

- (void)applicationWillResignActive:(UIApplication *)application {

    //works - but undesirable
    //[self addDummyView];
    //[_tabBarController.view snapshotViewAfterScreenUpdates:YES];
}

- (void)applicationDidEnterBackground:(UIApplication *)application {

    //does not work - needs to work to show dummyview only when application actually goes into the background
    [self addDummyView];
    [_tabBarController.view snapshotViewAfterScreenUpdates:YES];
}

- (void)addDummyView {

    UIView *topView = _tabBarController.view;
    UIView *colorView = [[UIView alloc] initWithFrame:topView.frame];
    [colorView setBackgroundColor:[UIColor blueColor]];
    [topView addSubview:colorView];
    [topView bringSubviewToFront:colorView];
}

Answer 1

You can get you answer here: Show splash screen when application enters background.

Keep your code in applicationWillResignActive.

Answer 2

When the applicationDidEnterBackground method returns, a snapshot of the current view of the app is taken to be used for the multitasking view. The reason that you are not seeing the update is because the snapshot is taken before the drawing cycle. Even if you call setNeedsDisplay the snapshot still is taken before.

To wait until the view updates (after you have added your subview) call this:

[self.view snapshotViewAfterScreenUpdates:YES];

with a value of YES. This forces your changes to render first. You can read more about handling stuff like this in apple docs here: https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgrammingGuide/StrategiesforHandlingAppStateTransitions/StrategiesforHandlingAppStateTransitions.html#//apple_ref/doc/uid/TP40007072-CH8-SW27

Answer 3

Your code is fine. You should know that applicationDidEnterBackground is not called when you double tap the home button. It is called when you switch to another app or go to springboard.

So, you should press the home button only once, then double tap it and the screenshot of your app should have the image view. I replicated your use case in a test project and it works for me.

If it still does not work, you should see if the image of the image view is not nil. Oh, and please don't hide the app window.