Detect when app finishes loading after opening from background

Question

When my app is first opened there is a long loading time so I can display a loading screen. When the user exits the app by clicking the home button then re-opens it (the viewDidLoad/viewDidAppear methods aren't called again) the app has another loading period, I guess while it's "waking up".

What method can I use to detect the user hitting the home button to send the app into the background and what method can I use to detect that the app has been revived from the background?

This should be sufficient enough to provide my loading screen properly but just in-case. Is there also a method for detecting when the loading has finished after a "revival"?

Answer 1

You can register a notification for UIApplicationWillEnterForegroundNotification. There you can do your stuff.

- (void)viewDidLoad
{
[super viewDidLoad];

// Register for the notifcation 
[[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(refreshView) name:UIApplicationWillEnterForegroundNotification object:nil];  

}  

-(void)refreshView
{
/* 
 Invoked when application enters foreground. Do your stuff

 */   

 }  

To remove observer

-(void)dealloc
{
  [[NSNotificationCenter defaultCenter] removeObserver:self];
  [super  dealloc];
}