iOS: Refresh Data When App is Brought to Foreground

Question

I'm getting data off the server via JSON and displaying it on Labels. I've added that method in viewDidLoad.

I want to refresh the data when the user opens the app again. Currently, even if I kill the app in the simulator and start the app again, it doesn't refresh.

I tried the viewDidAppear method, but it isn't being executed for some reason.

-(void)viewDidAppear{
        NSLog(@"Called viewDidAppear");
}

This is never called. I tried to minimize the app but it didn't work.

Answer 1

I followed this tutorial - http://leejon.es/notifying-a-viewcontroller-with-uiapplicationdidbecomeactivenotification/

First, attach to the notification in the viewWillAppear method of the target view controller:

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    [[NSNotificationCenter defaultCenter] addObserver: self
                                             selector: @selector( appActivated: )
                                                 name: UIApplicationDidBecomeActiveNotification
                                               object: nil];

}


- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self ];
}


- (void)appActivated:(NSNotification *)note
{
    [self update];
}

Answer 2

You can listen for notifications and respond appropriately. Try using these and decide what works for your intended workflow.

UIApplicationDidBecomeActiveNotification
UIApplicationWillEnterForegroundNotification

You can use respond to the notification like this.

[[NSNotificationCenter defaultCenter] addObserverForName: UIApplicationDidBecomeActiveNotification object: nil queue: [NSOperationQueue mainQueue] usingBlock:^(NSNotification *note) {
    // LOAD JSON
}];

Answer 3

The viewDidAppear: method takes a bool parameter wether the view was displayed with an animation which you are missing. Also you have to call the implementation of the superclass:

- (void)viewDidAppear:(BOOL)animated
{
   [super viewDidAppear: animated];
   NSLog(@"Called viewDidAppear");
}

Answer 4

In your app delegate implementation, there is a method called:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions;

This method is called each time the app is launched, so I think it fits your needs. If you place your code here, it should work.

Also, be aware you should not perform a synchronous call here, because you will delay the app launch.

EDIT: This method will be only called when the app launches. You could place your code inside a method, and call it from application didFinishLaunchingWithOptions, and then also call it from the method:

- (void)applicationWillEnterForeground:(UIApplication *)application;

This method will be called when the application enters the foreground, but not after the first launch, so beware.

I also think you should check the UIApplicationDelegate methods from apple developer page: http://developer.apple.com/library/ios/#documentation/uikit/reference/UIApplicationDelegate_Protocol/Reference/Reference.html Also, check out the application state changes: http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html