iPhone OS 4.0
The curtain has been pulled back on iPhone 4, and the list of new features is massive: There's multitasking (finally!), a refreshed interface, and literally hundreds of other changes, all coming this summer. Here's the full rundown.
The new OS will ship in June (Fall for iPad, and a developer preview is available today, so we can expect to have plenty of apps updated and ready for launch.
New Features: Multitasking, App Folders and More
Multitasking
• Multitasking: It's here, finally.
It's handled with a simple task switcher: double click your home button, and you get a list of running apps. Select, switch, done. Multitasking is limited to audio streaming, VoIP and GPS apps, as well as a few other allowances: they can finish specific, important tasks in the background, for example. As far as non-music/nav/VoIP apps, those can be suspended in the background, but not left running. (See below.) Full details here.
• Fast app switching: With iPhone 4's multitasking, most apps aren't actually running in the background—just certain functions of the app, like an audio stream or a GPS lock. But! All apps can now be frozen, in full, so that when you reopen them, they're restored to exactly the state they were in when they were closed.
• Local notifications: Notifications can be sent between apps on the phone, not just from remote servers. In other words, if something important happens in an app you've opened and moved away from, a notification will pop up in whatever app you're using at the time, effectively saying "switch back to me!" It's a fairly clever way to keep track of multiple apps without the need for a start bar or dock-type interface. From Apple's dev guidelines:
The advantage of local notifications is that they are independent of your application. Once a notification is scheduled, the system manages the delivery of it. Your application does not even have to be running when the notification is delivered.
Apple's official line:
_[iPhone OS](http://gizmodo.com/tag/iphoneos4/>iPhone OS 4's new multitasking offers users a new way to quickly move between apps, and provides developers seven new multitasking services to easily add multitasking features to their apps. These services include background audio, so apps like Pandora can play music in the background, and VoIP, so VoIP apps can receive a VoIP call even when the iPhone is asleep or the user is running other apps.