iOS monitor app resumes from background to foreground

1. the agent method in the Appdelegate can monitor the status of the switch before and after the program

- (void) Applicationdidenterbackground: (UIApplication *) application{NSLog (@"---applicationdidenterbackground----")    //Go Backstage}- (void) Applicationdidbecomeactive: (UIApplication *) application{NSLog (@"---applicationdidbecomeactive----")    //Access to reception}- (void) Applicationdidenterbackground: (UIApplication *) application{NSLog (@"---applicationdidenterbackground----")    //Go Backstage}- (void) Applicationdidbecomeactive: (UIApplication *) application{NSLog (@"---applicationdidbecomeactive----")    //Access to reception}

2. Single Viewcontroller listen by registering filter notifications in viewdidload to remove notifications in Dealloc

[[Nsnotificationcenter defaultcenter] addobserver:self                                          selector: @selector (someMethod1:)                                                Object

iOS monitor app resumes from background to foreground