iPad: new 4/5 finger multitasking gestures - when is the app's screenshot taken?

Question

When my app resigns activation it covers the current view with a black view to prevent iOS from taking a screenshot of the potentially sensitive document being shown.

When pushing the app to background this works fine. The screenshot is taken AFTER didEnterBackground. Using multitasking gestures to switch back shows the black view.

However with the new 4/5 finger gestures if you swipe left or right, first "resign activation" is triggered and then "did enter background" but the screenshot seems to be taken BEFORE these events. How to prevent it in that case?

Answer 1

If I understand correctly, you're trying to avoid this problem:

http://software-security.sans.org/blog/2011/01/14/whats-in-your-ios-image-cache-backgrounding-snapshot/

And the issue is that the behavior doesn't match what Apple documents here:

http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/CoreApplication/CoreApplication.html#//apple_ref/doc/uid/TP40007072-CH3-SW21

If that's true, then this definitely sounds like a bug -- but you do realize the gesture you mentioned is apparently a developer feature that's not available to the public (and under NDA)?

I'd do the following:

1. Sumbit a bug report - http://bugreport.apple.com/

2. Ask on the Apple Developer Forums (and include the bug number). People can speak freely there, and it's possible that an Apple developer will respond or at least notice your post (and hopefully prioritize the bug).

3. Finally, if you really want a response from Apple, then problems like this are a perfect use for your technical support incidents. You get 2 of these per year included with your ADC membership: http://developer.apple.com/support/resources/technical-support.html