applicationDidEnterBackground
applicationWillEnterForeground

这些所有在app app delegate中调用

These all called in the app delegate

所有细节都可以在这里找到： http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html

All details can be found here: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html