iOS: Terminating app in background after a certain period of time - objective-c

Question

I'm trying to implement a passcode lock feature in my app that lets the user choose how much time must go by before the passcode is required for reentry (similar to the passcode functionality of the OS). So for example the user may be able to select that they want the passcode to be required 5, 10, 20 minutes after exiting the app into the background.
I've tried to deal with presenting a passcode view in different ways, but it is often difficult to figure out the best way to present it, and so I had the idea that perhaps it is best to terminate the app after the time is up, and therefore I would only have to present the passcode screen when the app is launched.
Is this possible to do? I had two thoughts about ways to approach this.
1) Have an NSTimer within the app delegate, start it when the app goes into the background, and then when/if the timer reaches the set number of minutes, then terminate the app? I could see a number of things going wrong with this, for example if the OS terminated the app to free up memory sooner than the timer finished. Although that wouldn't be a huge issue.
2) Set an instance of NSDate when the app goes into the background. Then when the app is being launched, see if this date is more than x minutes ago, and present the passcode entry screen depending on that.
I feel like both of these are a little off. I'm inexperienced with Timers, RunLoops, etc, so any advice is appreciated.

Answer 1

Option 2 seems to be a good solution that we have used with success.

Answer 2

Option 2. Use the ApplicationDelegate Lifecycle methods to drive it.
application:didFinishLaunchingWithOptions:
applicationDidBecomeActive:
applicationWillResignActive:
applicationDidEnterBackground:
applicationWillEnterForeground:
applicationWillTerminate:
applicationDidFinishLaunching:
In the applicationWillResignActive method persist the current timestamp to your UserDefaults, and in the applicationWillEnterForeground check this against the current time and if the passcode interval has passed, present your passcode.
(probably best to clear the timestamp when you are active to minimise the chance of false triggering on receiving calls and SMS etc)
Depending on sensitivity you may want to prepare your views before entering foreground to obscure sensitive data, so they do not return in the unlocked state.

Answer 3

you can follow both for better result. for example use option 2 when app active from didFinishLaunchingWithOptions: and option 1 when application enable from
- (void)applicationDidBecomeActive:(UIApplication *)application or - (void)applicationWillEnterForeground:(UIApplication *)application
option 1-Easiest way is to schedule a NSTimer on the background run-loop. I suggest that the following code is implemented on your application delegate, and that you call setupTimer from applicationWillResignActive:.
- (void)applicationWillResignActive:(UIApplication *)application
{
[self performSelectorInBackground:#selector(setupTimerThread) withObject:nil];
}
-(void)setupTimerThread;
{
  NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
  NSTimer* timer = [NSTimer timerWithTimeInterval:10 * 60 target:self selector:#selector(triggerTimer:) userInfo:nil repeats:YES];
  NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
  [runLoop addTimer:timer forModes:NSRunLoopCommonModes];
  [runLoop run];
  [pool release];
}
-(void)triggerTimer:(NSTimer*)timer;
{
  // Do your stuff
}
in appDelegate .h
UIBackgroundTaskIdentifier bgTask;
in appDelegate .m
- (void)applicationDidEnterBackground:(UIApplication *)application
{
UIApplication* app = [UIApplication sharedApplication];
// Request permission to run in the background. Provide an
// expiration handler in case the task runs long.
NSAssert(bgTask == UIBackgroundTaskInvalid, nil);
bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
// Synchronize the cleanup call on the main thread in case
// the task actually finishes at around the same time.
dispatch_async(dispatch_get_main_queue(), ^{
if (bgTask != UIBackgroundTaskInvalid)
{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}
});
}];
// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
// Do the work associated with the task.
// Synchronize the cleanup call on the main thread in case
// the expiration handler is fired at the same time.
dispatch_async(dispatch_get_main_queue(), ^{
if (bgTask != UIBackgroundTaskInvalid)
{
[app endBackgroundTask:bgTask];
bgTask = UIBackgroundTaskInvalid;
}
});
});
NSLog(#"app entering background");
/*
Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
*/
}
OR you could run the NSTimer on a background thread by with something like this (I am intentionally leaking the thread object):
-(void)startTimerThread;
{
  NSThread* thread = [[NSThread alloc] initWithTarget:self selector:#selector(setupTimerThread) withObject:nil];
  [thread start];
}
try with this above code. we use both options its works fine for us. good luck