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Multitasking (iOS)

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On iOS, multitasking is a feature available in iOS 4 or later that allows multiple applications to run and perform tasks at the same time.

Multitasking for iOS was first released in June 2010 along with the release of iOS 4.0.[1][2] Only certain devices—iPhone 4, iPhone 3GS, and iPod Touch 3rd generation—were able to use multitasking.[3] The iPad did not get multitasking until the release of iOS 4.2.1 in November 2010.[4] Currently, multitasking is supported on iPhone 3GS or newer, iPod Touch 3rd generation or newer, and all iPad models.[5]

Implementation of multitasking in iOS has been criticized for its approach, that limits the work that applications in the background can perform to a limited function set, and for requiring application developers to add explicit support for it.[3][6]

Features

Background APIs

File:IOS 7 Multitasking Switcher.jpg|thumb|Multitasking on iOS 7]]

Before iOS 4, multitasking was limited to a selection of the applications Apple included on the device. Users could, however "jailbreak" their device in order to unofficially multitask.[7] Starting with iOS 4, on third-generation and newer iOS devices, multitasking is supported through seven background APIs:[8]

  1. Background audio – application continues to run in the background as long as it is playing audio or video content[9]
  2. Voice over IP – application is suspended when a phone call is not in progress[10]
  3. Background location – application is notified of location changes[10]
  4. Push notifications
  5. Local notifications – application schedules local notifications to be delivered at a predetermined time[10]
  6. Task completion – application asks the system for extra time to complete a given task[10]
  7. Fast app switching – application does not execute any code and may be removed from memory at any time[10]

In iOS 5, three new background APIs were introduced:

  1. Newsstand – application can download content in the background to be ready for the user[10]
  2. External Accessory – application communicates with an external accessory and shares data at regular intervals[10]
  3. Bluetooth Accessory – application communicates with a bluetooth accessory and shares data at regular intervals[10]

In iOS 7, Apple introduced a new multitasking feature, providing all apps with the ability to perform background updates. This feature prefers to update the user's most frequently used apps and prefers to use WiFi networks over a cellular network, without markedly reducing the device's battery life.

Fast app switching

Fast app switching allows apps to pause and resume themselves quickly and easily change to other apps.[11] An app that is on the screen is considered "running", while an app that is not on screen but is still in memory is considered "suspended".[12] All apps that are built with iOS 4 SDK support fast app switching if running on iOS 4 and a compatible device.[10] Users can utilize fast app switching by activating the multitasking bar, which can be displayed by double-tapping the home button.[3][12]

Task completion

Task completion allows apps to continue a certain task after the app has been suspended.[13][14] As of iOS 4.0, apps can request up to ten minutes to complete a task in the background.[15]

See also

References

  1. ^ "iOS 4 iPhone Update RELEASED: A Guide To iOS 4". The Huffington Post. June 21, 2010. Retrieved April 13, 2013.
  2. ^ Albanesius, Chloe (June 21, 2010). "Apple iPhone iOS 4 Software Update Expected Monday". PC Magazine. Retrieved April 14, 2013.
  3. ^ a b c Cheng, Jacqui (June 21, 2010). "Ars reviews iOS 4: what's new, notable, and what needs work". Ars Technica. Retrieved April 14, 2013.
  4. ^ Ray, Bill (November 22, 2010). "iOS 4.2 multi-tasking comes to the iPad". The Register. Retrieved April 14, 2013.
  5. ^ "iOS: Understanding multitasking". Apple. Retrieved 2013-09-14.
  6. ^ Newman, Jared (June 22, 2010). "Multitasking With iOS 4 is Horrible: Apple Blew It". PC World. Retrieved April 14, 2013.
  7. ^ Ritchie, Rene (2010-06-14). "iOS 4 walkthrough". iMore. Retrieved 2013-09-14.
  8. ^ Ritchie, Rene (2010-04-08). "Apple announces multitasking for iPhone OS 4 (iPhone 3GS/iPod touch G3 only)". iMore. Retrieved 2013-09-14.
  9. ^ "iOS App Programming Guide: App States and Multitasking". Apple Developer. Retrieved 2013-09-14.
  10. ^ a b c d e f g h i "What's New in iOS: iOS 4.0". Apple Developer. Retrieved 2013-09-14.
  11. ^ Shimpi, Anand (June 22, 2010). "Apple's iOS 4 Explored". AnandTech. Retrieved April 14, 2013.
  12. ^ a b Perenson, Melissa (June 8, 2010). "Multitasking on Apple's iPhone 4: How Does It Work?". PC World. Retrieved April 14, 2013.
  13. ^ Snell, Jason (April 8, 2010). "Inside iPhone 4.0's multitasking". Macworld. Retrieved April 14, 2013.
  14. ^ "Apple iPhone 4". CNET. June 23, 2010. Retrieved April 14, 2013.
  15. ^ Hollington, Jesse (June 21, 2010). "Instant Expert: Secrets & Features of iOS 4". iLounge. Retrieved April 14, 2013.
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