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How does multi-tasking work on the iPhone 4 (iOS4) Wednesday, 23/06/2010 by nik
iPhone multi-tasking is not "true" multi-tasking. You might be surprised to learn this, as I was. But Apple has a system that mimics multitasking as a way of preserving battery power. Clever stuff. This article describes how it's done.
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So how is Apple making this magic happen? Here's a breakdown of just exactly what multitasking really means (and feels like) on the new iPhone (and the 3GS):
- Fast app switching: You know how you can leave off in Mail halfway through writing a response and go back to exactly where you were? Well that happens everywhere now. When you leave the app, you go back in exactly the same place. And it happens quickly. Fast app switching is essentially like toggling between "paused" applications. This combined with Apple's new app switcher (double tap the home button to bring up your most recently used apps) destroys that annoying iPhone feeling of going in and out and in and out. It just doesn't exist anymore, provided all your apps are up to date, which is going to take some time. It's amazing how much this single feature counts -- it's definitely one of the prime movers here, and it's so simple it's stupid. We would have liked to see options for "favorite" apps or some way to prioritize what you're switching to, but once you get used to this system -- which just puts whatever you've used most recently to the far left -- it makes some sense.
- Task completion: Basically, task completion lets an app do its thing even if you leave it. So if you're uploading or downloading a picture in Evernote or Dropbox, or saving an article in theNew York Times app, even if you navigate away, the job is done when you get back to the app. This accounts for a lot of what we think of as multitasking. Most of your apps are just idling -- it's only when you interact with them that it counts. We don't know the boundaries for this API, though it seems to leave a lot of room for creative use. We know it's not just big jobs, it's little ones too -- Colloquy uses this feature to keep you connected to your IRC host. To be honest, that kind of behavior is one thing we thought we wouldn't see in iOS 4, and here it is. Hopefully Twitter app devs and other instant messaging clients will utilize the API in a similar manner.
- Background audio and VoIP: These two are straightforward. The first allows for music playing apps to keep their stream running in the background (and even gives them little widget controls in the app switcher), and the second allows VoIP connections to stay active. That means you can stay on a Skype call and go check your mail, but it also means that the VoIP connection will be aware of incoming calls when you're not actively using an app. Additionally, this API can be used to allow for recording even if you exit an app, as demonstrated effectively in the new version of Evernote.
- Background GPS: Basically, GPS apps can keep running in the background... for obvious reasons. This one will drain your battery if you're not docked -- but who's using a GPS app and not plugging that thing in? Okay, we might be a little guilty of that. Regardless, this will keep your navigation software afloat if you have to take a call, and apparently will let GPS-centric apps like FourSquare check in even if you're not running it in the foreground.
Apple combines these heavy hitters with more familiar tricks, like push notifications, to excellent effect. [source engadget]
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