Switching the view after applicationDidBecomeActive - ios

Question

I am currently developing an app that will need to return to another view after running in the background for more than five minutes. In order to do this, I will have to have a timer running in the background after the the Home button has been pressed or in case of an interruptions such as an SMS or a telephone call, then, after five minutes the app will need to go to another view. I know that the applicationDidBecomeActive method will have to be used, but how? I also know that a view can be refreshed in applicationDidBecomeActive but how is that done? ( I am not using storyboards.)

Answer 1

Actually, you should do this with the applicationDidEnterBackground applicationWillEnterForeground delegate methods of UIAppDelegate or by registering to the appropriate system notifications (didBecomeActive is called on other occasions too, such as when a UIAlertView is dismissed from screen).
This should be something in the lines of (may include syntax problems, I'm textbox-coding here):
In the viewDidLoad method of your view controller, register to the notifications:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(willEnterForeground:) name:UIApplicationWillEnterForegroundNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(didEnterBackground:) name:UIApplicationDidEnterBackgroundNotification object:nil];
Implement the willEnterForeground: and didEnterBackground: methods. In willEnterForeground: sample the current time using CACurrentMediaTime() or [NSDate date]. In didEnterBackground: sample the time again and calculate the time difference. Since this method is implemented inside the view controller, you can manipulate the subviews of your self.view as you wish.
Do not forget to remove the observers on your dealloc method (viewDidUnload is deprecated since iOS 6.0, so beware):
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationDidEnterBackgroundNotification object:nil]
[[NSNotificationCenter defaultCenter] removeObserver:self name:UIApplicationWillEnterForegroundNotification object:nil]

Answer 2

Here's how you can do it. I just made a test app and I confirm that it works beautifully. Code:
#import "AppDelegate.h"
#import "ViewController.h"
#import "theView.h"
NSTimer *theTimer;
UIViewController *theViewController;
BOOL theTimerFired = NO;
#implementation AppDelegate
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.viewController = [[ViewController alloc] initWithNibName:#"ViewController" bundle:nil];
self.window.rootViewController = self.viewController;
[self.window makeKeyAndVisible];
return YES;
}
- (void)applicationWillResignActive:(UIApplication *)application
{
// Set a 5 minute timer (300 seconds)
theTimer = [NSTimer scheduledTimerWithTimeInterval:300.0 target:self selector:#selector(presentVC) userInfo:nil repeats:NO];
}
- (void)presentVC
{
// Set a boolean to indicate the timer did fire
theTimerFired = YES;
}
- (void)applicationDidBecomeActive:(UIApplication *)application
{
// Check to see if the timer did fire using the previous boolean we created
if (theTimerFired == YES)
{
theViewController = [[UIViewController alloc]initWithNibName:#"theView" bundle:nil];
[self.viewController presentViewController:theViewController animated:YES completion:NULL];
[theTimer invalidate];
}
}
#end