Question

I´m working on an application in which, when it is pushed in background via the home button, a timer should start and when the application gets back to foreground and the timer has passed a certain amount of time, something should be executed.

My questions are

1. How do I handle the events when my app goes to
   background/foreground?
2. Is there a special method or an other technique?

Thanks a lot.

Answer 1

A possible implementation could look like:

#define YOUR_TIME_INTERVAL 60*60*5   //i.e. 5 hours

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    //... your oder code goes here

    NSNumber *timeAppClosed = [NSNumber numberWithDouble:[[NSDate date] timeIntervalSince1970]];
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults timeAppClosed forKey:@"time.app.closed"];
    [defaults synchronize];
}

and

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    NSNumber *timeAppClosed = [[NSUserDefaults standardUserDefaults] valueForKey:@"time.app.closed"];
    if(timeAppClosed == nil)
    {
        //No time was saved before so it is the first time the user
        //opens the app
    }
    else if([[NSDate date] timeIntervalSinceDate:[NSDate dateWithTimeIntervalSince1970:[timeAppClosed doubleValue]]] > YOUR_TIME_INTERVAL)
    {
        //Place your code here
    }
}