Can an app keep running while the screen is locked, on a jailbroken iphone?

Question

I have an idea for an app that I'd like to develop, but before I invest a lot of time learning objective C and the iOS APIs, I'd like to make sure that what I want to do is feasible.

The app I want to make is a purely auditory (sound-only) version of Google Glass. I'm visually impaired, so spending a lot of money on something visual, even though it can read content to you, would not be worth it. But if I could use an iPhone to give many of the same options as Google Glass, that would be great.

Many times, I've wanted a piece of information while walking down the street, where I couldn't easily get to my iPhone, because I have my cane in one hand, and something else in the other. In such cases, it'd be awesome if I could say a command, and get a voice response.

I'd use the microphone built into the Apple earphones for audio input, but I'm not sure if it's possible to listen for audio input while the screen is locked. I'm certain it's not possible with a non-jailbroken iPhone.

Can anyone can tell me if this is possible?

Answer 1

Yes, you can do this.

In order to keep your app running all the time, even when the iPhone is locked, you could build a Launch Daemon. A launch daemon can start when the phone does, and is not subject to the restrictions that iOS puts on sandboxed apps, installed to /var/mobile/Applications/.

You do need to have a jailbroken device to take advantage of Launch Daemons. Here is a good tutorial on building one.

Launch Daemons are also a normal part of OS X, so if you need more information, you might try consulting the OS X docs online. Most aspects of Launch Daemons work the same way on a jailbroken iPhone.

You'll also want to be able to detect certain events, to activate your app. You certainly don't want to be processing an audio stream at all times (maybe you only activate the app when you start walking with your cane). To detect events, like a home button press (or however you want to activate your code), I would take a look at RPetrich's libactivator library.