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POhow can I let UIPageViewController know when my async download is complete?
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copied!<p>I currently have a UIPageViewController set up in my project almost exactly like the default page-based application template. </p> <p>However, in the init method for my ModelController I am using NSURLConnection to async download data into an array (of images) that is supposed to be displayed on the PageViewController. </p> <p>That means when my root view controller goes and inits a starting view controller the resources might not be downloaded yet and then the model controller is fetching things from an empty array which crashes the app.</p> <p>How can I implement a safe way to show the images in a PageView? I was thinking of using an empty view controller with an activity indicator as the starting view controller but I don't know how I'd then let the model controller know when the download is completed so I can then update the views with the images.</p> <p><strong>my root view controller (this is the uipageviewcontroller delegate)</strong></p> <pre><code>@interface CSAPromoViewController () @property (readonly, strong, nonatomic) CSAPromoModelController *modelController; @end @implementation CSAPromoViewController @synthesize modelController = _modelController; - (void)viewDidLoad { [super viewDidLoad]; self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil]; self.pageViewController.delegate = self; CSAPageDataViewController *startingViewController = [self.modelController viewControllerAtIndex:0 storyboard:self.storyboard]; NSArray *viewControllers = @[startingViewController]; [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil]; self.pageViewController.dataSource = self.modelController; [self addChildViewController:self.pageViewController]; [self.view addSubview:self.pageViewController.view]; //set page view controller's bounds CGRect pageViewRect = self.view.bounds; self.pageViewController.view.frame = pageViewRect; [self.pageViewController didMoveToParentViewController:self]; self.view.gestureRecognizers = self.pageViewController.gestureRecognizers; } </code></pre> <p><strong>my model controller (this is the data source)</strong></p> <pre><code>@interface CSAPromoModelController() @property (readonly, strong, nonatomic) NSArray *promosArray; @end @implementation CSAPromoModelController -(id)init { self = [super init]; if (self) { NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://blah.com"] cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:60.0]; [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) { _promosArray = [self parseJSON:data]; }]; } return self; } - (CSAPageDataViewController *)viewControllerAtIndex:(NSUInteger)index storyboard:(UIStoryboard *)storyboard { // Return the data view controller for the given index. if (([self.promosArray count] == 0) || (index >= [self.promosArray count] / 2)) { return nil; } // Create a new view controller and pass suitable data. CSAPageDataViewController *dataViewController = [storyboard instantiateViewControllerWithIdentifier:@"CSAPageDataViewController"]; dataViewController.promoOne = [self.promosArray objectAtIndex:index * 2]; dataViewController.promoTwo = [self.promosArray objectAtIndex:(index * 2) + 1]; return dataViewController; } </code></pre> <p><strong>the data view controller</strong></p> <pre><code>@implementation CSAPageDataViewController - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view. self.promoLabelTop.text = [self.promoOne name]; self.promoImageTop.image = [self.promoOne image]; self.promoLabelBottom.text = [self.promoTwo name]; self.promoImageBottom.image = [self.promoTwo image]; } </code></pre>

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