view controller variables in ApplicationWillResignActive

Question

I'm trying to make my timer "run" in the background by saving the time to disk on entering background and retrieving it on entering foreground. Each view controller has a timer and a timeInterval specified by the user. The problem is, I don't know how to access the timeInterval variable. I think I can get the difference of time by using something like this (would this work?):

NSTimeInterval idleTime = [dateReturnedToForeground timeIntervalSinceDate:dateEnteredBackground];
NSTimeInterval elapsedTime = [[NSDate date] timeIntervalSinceDate:startDate];
elapsedTime -= idleTime;

Each view controller (and timer/time interval) is accessed like this:

-(void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    DetailViewController *detailVC;
    if (![self.detailViewsDictionary.allKeys containsObject:indexPath]){
        detailVC = [[DetailViewController alloc]initWithNibName:@"DetailViewController" bundle:nil];
        [self.detailViewsDictionary setObject:detailVC forKey:indexPath];
        detailVC.context = self.managedObjectContext;
    }else{
        detailVC = self.detailViewsDictionary[indexPath];
    }
        Tasks *task = [[self fetchedResultsController] objectAtIndexPath:indexPath];
        detailVC.testTask = task;
        [[self navigationController] pushViewController:detailVC animated:YES];
    NSLog(@"%@", self.detailViewsDictionary);
    [[NSNotificationCenter defaultCenter] addObserver:detailVC forKeyPath:self.detailViewsDictionary[indexPath] options:nil context:nil];
}

I am adding each view controller to the Notification Center so it can be accessed in the app delegate (i think this is right?). Problem is, I don't know how to combine the first code with the view controller code, because I can't access the view controller's properties in the app delegate. Any suggestions so that I can make my timer "run" in the background?

Answer 1

You are going about this all wrong. There is no need to do any of this in the app delegate.

Have each view controller listen for the UIApplicationWillResignActiveNotification notification. Then each view controller can do whatever it feels is appropriate to save its data when the notification is received.

Update:

In the view controller's init... method, register for the notification:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(resigningActive) name:UIApplicationWillResignActiveNotification object:nil];

In the view controller's dealloc method, unregister:

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillResignActiveNotification object:nil];
}

Then implement the resigningActive method:

- (void)resigningActive {
    // The app is resigning active - do whatever this view controller needs to do
}