製作pageViewController NSURLSession完成後

Question

我是一個新手，在編碼objective-c。

我目前正在做一個練習應用程序，我需要從一個NSURLSession的API中獲取一些json數據並將日期發送到一個PageViewController。

因此，目前我在getWeer方法中獲取我的json數據，在調用pageViewController（在viewDidLoad中）之前調用該方法。但是因爲NSURLSession運行異步，我認爲並不完整，當我嘗試在我的pageViewController中訪問它時，json-data始終爲空。

如何在NSURLSession完成後製作pageViewController？

@interface SecondViewController()<CLLocationManagerDelegate> 
@property (nonatomic, strong) CLLocationManager *locationManager; 
@property (nonatomic, strong) NSString *AppId; 
@property (nonatomic, weak) NSDictionary *json; 
@end 

@implementation SecondViewController 

- (void)viewDidLoad { 
    [super viewDidLoad]; 
    self.AppId = @"feda1f13263bb730deeb89fb3936a76e"; 
    self.locationManager = [[CLLocationManager alloc] init]; 
    self.locationManager.delegate = self; 
    self.locationManager.desiredAccuracy = kCLLocationAccuracyBest; 

    [[self locationManager] requestWhenInUseAuthorization]; 
    [[self locationManager] startUpdatingLocation]; 

    [self getWeer]; 


    // Create page view controller 
    self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PageViewController"]; 
    self.pageViewController.dataSource = self; 

    PageContentViewController *startingViewController = [self viewControllerAtIndex:0]; 
    NSArray *viewControllers = @[startingViewController]; 
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil]; 

    // Change the size of page view controller 
    self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 30); 

    [self addChildViewController:_pageViewController]; 
    [self.view addSubview:_pageViewController.view]; 
    [self.pageViewController didMoveToParentViewController:self]; 


} 

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

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

    // Create a new view controller and pass suitable data. 
    PageContentViewController *pageContentViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PageContentViewController"]; 

    pageContentViewController.pageIndex = index; 
    NSLog(@"%@",self.json); 
    pageContentViewController.json = self.json; 

    return pageContentViewController; 
} 

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

    NSUInteger index = ((PageContentViewController*) viewController).pageIndex; 

    if ((index == 0) || (index == NSNotFound)) { 
     return nil; 
    } 

    index--; 
    return [self viewControllerAtIndex:index]; 
} 

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

    NSUInteger index = ((PageContentViewController*) viewController).pageIndex; 

    if (index == NSNotFound) { 
     return nil; 
    } 

    index++; 
    if (index == 3) { 
     return nil; 
    } 
    return [self viewControllerAtIndex:index]; 
} 

- (NSInteger)presentationCountForPageViewController:(UIPageViewController *)pageViewController{ 
    return 3; 
} 

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController{ 
    return 0; 
} 

-(void)getWeer{ 
    NSString *dataUrl = [NSString stringWithFormat:@"http://api.openweathermap.org/data/2.5/forecast/daily?lat=%f&lon=%f&cnt=4&&APPID=%@&units=metric&lang=nl", self.locationManager.location.coordinate.latitude, self.locationManager.location.coordinate.longitude, self.AppId]; 

    NSLog(@"%f",self.locationManager.location.coordinate.latitude); 
    NSLog(@"%f",self.locationManager.location.coordinate.longitude); 
    NSURL *url = [NSURL URLWithString:dataUrl]; 

    NSURLSession *session = [NSURLSession sharedSession]; 
    NSURLSessionDataTask *dataTask = [session dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) { 
     dispatch_async(dispatch_get_main_queue(), ^{ 
      self.json = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil]; 
     }); 
    }]; 
    [dataTask resume]; 
} 

@end 

Answer 1

異步完成後調用此方法。

// Create page view controller 
-(void)setupPageViewController { 
     self.pageViewController = [self.storyboard instantiateViewControllerWithIdentifier:@"PageViewController"]; 
     self.pageViewController.dataSource = self; 

    PageContentViewController *startingViewController = [self viewControllerAtIndex:0]; 
    NSArray *viewControllers = @[startingViewController]; 
    [self.pageViewController setViewControllers:viewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil]; 

    // Change the size of page view controller 
    self.pageViewController.view.frame = CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height - 30); 

    [self addChildViewController:_pageViewController]; 
    [self.view addSubview:_pageViewController.view]; 
    [self.pageViewController didMoveToParentViewController:self]; 
}