Page View Controller: UILabel и UIImageview пустые на первой странице

Question

Я использую UIPageViewController для отображения элементов из файла JSON. Он отлично работает, за исключением первой страницы, которая ничего не отображает при загрузке, но если я вернусь, она будет работать.

код выглядит следующим образом:

#import "SJPagesViewController.h" 
#import "SJChildViewController.h" 

@interface SJPagesViewController() 

@end 

@implementation SJPagesViewController 
@synthesize urlToFollow, data,articlesArray; 

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil 
{ 
    ... 
} 

- (void)viewDidLoad 
{ 
    [super viewDidLoad]; 

    self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil]; 

    CGFloat window_height = ([self window_height]-30.0); 
    CGFloat window_width = [self window_width]; 
    CGRect pageFrame = CGRectMake(0.0f, 0.0f,window_width , window_height); 

    self.pageController.dataSource = self; 
    [[self.pageController view] setFrame:pageFrame]; 

    SJChildViewController *initialViewController = [self viewControllerAtIndex:0]; 

    NSArray *viewControllers = [NSArray arrayWithObject:initialViewController]; 

    [self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil]; 

    [self addChildViewController:self.pageController]; 
    [[self view] addSubview:[self.pageController view]]; 
    [self.pageController didMoveToParentViewController:self]; 


    //Download JSON 
    NSError *error=nil; 

    NSURL *url = [NSURL URLWithString:urlToFollow]; 

    data = [NSData dataWithContentsOfURL: url options:NSDataReadingMappedIfSafe error:&error]; 
    NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error]; 

    NSArray *response = [dictionary objectForKey:@"items"]; 

    articlesArray = [[NSArray alloc] initWithArray:response]; 
    //NSLog(@"articlesArray = %@", articlesArray); 


} 

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerBeforeViewController:(UIViewController *)viewController { 

    NSUInteger index = [(SJChildViewController *)viewController index]; 

    if (index == 0) { 
     return nil; 
    } 
    index--; 

    return [self viewControllerAtIndex:index]; 
} 

- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController { 

    NSUInteger index = [(SJChildViewController *)viewController index]; 
    index++; 

    if (index == articlesArray.count) { 
     return nil; 
    } 

    return [self viewControllerAtIndex:index]; 

} 

- (CGFloat) window_height { 
    return [UIScreen mainScreen].applicationFrame.size.height; 
} 

- (CGFloat) window_width { 
    return [UIScreen mainScreen].applicationFrame.size.width; 
} 

- (void)didReceiveMemoryWarning 
{ 
    [super didReceiveMemoryWarning]; 
    // Dispose of any resources that can be recreated. 
} 

- (SJChildViewController *)viewControllerAtIndex:(NSUInteger)index { 

    SJChildViewController *childViewController = [[SJChildViewController alloc] initWithNibName:@"SJChildViewController" bundle:nil]; 
    childViewController.index = index; 
    childViewController.arrayCount = self.articlesArray.count; 
    childViewController.model = [[self.articlesArray objectAtIndex:index]objectForKey:@"modelo"]; 
    childViewController.price = [[self.articlesArray objectAtIndex:index]objectForKey:@"precio"]; 
    childViewController.make = [[self.articlesArray objectAtIndex:index]objectForKey:@"marca"]; 
    childViewController.imageUrl = [[self.articlesArray objectAtIndex:index]objectForKey:@"photoUrl"]; 

    return childViewController; 

} 

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController { 
    // The number of items reflected in the page indicator. 
    if (articlesArray.count >5) { 
     return 5; 
    }else return [articlesArray count]; 
} 

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController { 
    // The selected item reflected in the page indicator. 
    return 0; 
} 

@end 

И ChildViewController для отображения элементов:

@implementation SJChildViewController 
@synthesize activityIndicator,imageUrl,price,model,make; 

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil 
{ 
    .... 
} 

- (void)viewDidLoad 

{ 
    [super viewDidLoad]; 

    //Activity indicator 
    activityIndicator = [[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray]; 
    activityIndicator.center = CGPointMake(self.view.frame.size.width/2.0, self.view.frame.size.height/2.0); 
    [self.view addSubview: activityIndicator]; 

    [activityIndicator startAnimating]; 

} 
-(void)viewDidAppear:(BOOL)animated{ 
    self.scrrenNumber.text = [NSString stringWithFormat:@"Artículo %ld de %ld", ((long)self.index+1), (long)self.arrayCount]; 

    self.lblMake.lineBreakMode = NSLineBreakByWordWrapping; 
    self.lblMake.text = [NSString stringWithFormat:@"%@",make]; 

    //Donload image 
    //Download image from url 
    NSURL *url_1= [NSURL URLWithString:imageUrl]; 
    NSURLRequest *request_1 = [NSURLRequest requestWithURL:url_1]; 
    [NSURLConnection sendAsynchronousRequest:request_1 
             queue:[NSOperationQueue currentQueue] 
          completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){ 
           UIImage *img = [UIImage imageWithData:data]; 
           [self.articleImage performSelectorOnMainThread:@selector(setImage:) withObject:img waitUntilDone:YES]; 
          }]; 
    //Activity indicator 

    self.lblPrice.text = [NSString stringWithFormat:@"%@",price]; 
    self.lblModel.lineBreakMode = NSLineBreakByWordWrapping; 
    self.lblModel.text = [NSString stringWithFormat:@"%@",model]; 
    [activityIndicator stopAnimating]; 
} 

Как я могу заставить его работать с первого момента?

Answer 1

Luis, у меня нет доступа к xcode прямо сейчас, но, похоже, ваша проблема в том, что вы создаете экземпляр childViewController, а articlesArray пуст.

В viewDidLoad вы загружаете свой json-файл и заселяете articlesArray после вызова вашего вспомогательного метода viewControllerAtIndex.

Попробуйте загрузить ваш json-файл и заполнить массив первым, как у вас здесь.

//Download JSON 
NSError *error=nil; 

NSURL *url = [NSURL URLWithString:urlToFollow]; 

data = [NSData dataWithContentsOfURL: url options:NSDataReadingMappedIfSafe error:&error]; 
NSDictionary *dictionary = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error]; 

NSArray *response = [dictionary objectForKey:@"items"]; 

articlesArray = [[NSArray alloc] initWithArray:response]; 

Затем создайте свой pageViewController и заполните его, как здесь.

self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil]; 

CGFloat window_height = ([self window_height]-30.0); 
CGFloat window_width = [self window_width]; 
CGRect pageFrame = CGRectMake(0.0f, 0.0f,window_width , window_height); 

self.pageController.dataSource = self; 
[[self.pageController view] setFrame:pageFrame]; 

SJChildViewController *initialViewController = [self viewControllerAtIndex:0]; 

NSArray *viewControllers = [NSArray arrayWithObject:initialViewController]; 

[self.pageController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil]; 

[self addChildViewController:self.pageController]; 
[[self view] addSubview:[self.pageController view]]; 
[self.pageController didMoveToParentViewController:self];