在锁定iOS设备的同时保持应用程序运行？

Question

I have an app that makes heavy use of video out. In a typical use-case, I'll have an iPad connected to an external monitor. I just want the external monitor on; the iPad display does not need to stay on.

The ideal case would be for someone to connect to an external monitor, then lock their iPad. But that pauses my app. (Currently, I'm calling setIdleTimerDisabled to keep the iPad from locking up and pausing my app.)

I'd like to give the user the option of locking the iPad, but still having my app running and sending images to video out. (Note: I'm not talking about keeping my app running when it's not in the foreground. I just want to keep it running while it's in the foreground, but the device is locked.)

Is this possible?

Answer 1

I would say no, it is not possible. Here's why:

The docs read:

Pressing the Sleep/Wake button is another type of interruption that causes your app to be deactivated temporarily. When the user presses this button, the system disables touch events, moves the app to the background but sets the value of the app's applicationState property to UIApplicationStateInactive (as opposed to UIApplicationStateBackground ), and finally locks the screen.

Something interesting to note in the docs above is that a bit further down under "What to do when an interruption occurs" Apple recommends that you stop doing certain tasks.

In response to this change, your app should do the following in its applicationWillResignActive: method:

• Stop timers and other periodic tasks.
• Stop any running metadata queries.
• Do not initiate any new tasks.
• Pause movie playback (except when playing back over AirPlay).
• Enter into a pause state if your app is a game.
• Throttle back OpenGL ES frame rates.
• Suspend any dispatch queues or operation queues executing non-critical code. (You can continue processing network requests and other time-sensitive background tasks while inactive.)

This tells me that Apple doesn't want or expect your app to be doing much of anything in this state, other than preparing to be fully backgrounded.

On a related note here's a thread that shows how to determine whether you've hit the Sleep/Wake button or not:

Is it possible to distinguish between locking the device and sending an app to background?