... 41 3■Opting out of the background state 41 421.3 Using fast app switching 41 4 Building a simple application for fast app switching 41 4Updating the user interface in the view controller 41 621 .4 ... controllers 144 7.7 Summary 145 8 Data: actions, preferences, and files 146 8.1 Accepting user actions 147 8.2 Maintaining user preferences 148 Creating your own preferences 149 ■Using the system ... audio playing in the background 43 7 Adding the UIBackgroundModes in Info.plist 43 7Handling the remote-control events 43 822 .4 Building the background audio application 43 922.5 Summary 44 1appendix...