自从上次在iOS上打开应用程序多久以来？

Question

How can I tell the time from the last time my app was open? Can this still be monitored even my app is not running in the background?

Thanks.

Answer 1

Put something like

[[NSUserDefaults standardUserDefaults] setObject:[NSDate date] forKey:@"kLastCloseDate"];

in both

- (void)applicationWillTerminate:(UIApplication *)application
- (void)applicationDidEnterBackground:(UIApplication *)application

Then check the difference at startup:

NSDate *lastDate = [[NSUserDefaults standardUserDefaults] objectForKey:@"kLastCloseDate"];
NSTimeInterval timeDiff = [[NSDate date] timeIntervalSinceDate:lastDate];
// your stuff

in both

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
- (void)applicationWillEnterForeground:(UIApplication *)application

Answer 2

In your application delegates - (void)applicationDidEnterBackground:(UIApplication *)application method, just write the current time to a file. Then, in either applicationWillEnterForeground: or applicationDidFinishLaunching , read this file and compare with the current time. The difference will tell you how long since your application was last foremost.