Question

I am back again and this will be my second question of the day.

Anyways, I am using NSJSONSerialization to parse a data from my website. The data is in array format so I am using NSMutableArray. The problem is, I can’t access the data stored in NSMutableArray from different view controllers.

FirstView.h

#import <UIKit/UIKit.h>

@interface FirstViewController : UIViewController

@property (nonatomic, strong) NSMutableArray *firstViewControllerArray;

@end

FirstView.m

- (void)ViewDidLoad
{
    [super viewDidLoad];

    NSURL *url = [NSURL URLWithString:@"http://j4hm.t15.org/ios/jsonnews.php"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    NSOperationQueue *queue = [[NSOperationQueue alloc]init];

    [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
            self.firstViewControllerArray = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];
    }];

    [self loadArray];
}

- (void)loadArray
{
    NSMutableArray *array = [NSMutableArray arrayWithArray:[self firstViewControllerArray]];

    //I also tried codes below, but it still won't work.
    //[[NSMutableArray alloc] initWithArray:[self firstViewControllerArray]];
    //[NSMutableArray arrayWithArray:[self.firstViewControllerArray mutableCopy]];

    NSLog(@"First: %@",array);

    SecondViewController *secondViewController = [[SecondViewController alloc] init];
    [secondViewController setSecondViewControllerArray:array];
    [[self navigationController] pushViewController:secondViewController animated:YES];
}

Second.h

#import <UIKit/UIKit.h>

@interface SecondViewController : UIViewController

@property (nonatomic, strong) NSMutableArray *secondViewControllerArray;

@end

Second.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSLog(@"Second: %@", [self secondViewControllerArray]);
}

Output

The NSLog(@"First: %@",array); will output the array hence it won’t be passing the SecondViewController a (null) value of the array.

However, NSLog(@"Second: %@", [self secondViewControllerArray]); will output (null). Am I missing something?

Answer 1

I don’t believe your download is completing before you push your new view controller onto the stack, and also set that view controller’s array property. Right now, you’re calling -loadArray right after you tell NSURLConnection to download data asynchronously. This download is going to finish long after you try to access the array property.

Try move the call to -loadArray within the asynchronous completion block (as seen below). Since this block is called when the download completes, you should have your data when you push the second view controller.

[NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
        self.firstViewControllerArray = [NSJSONSerialization JSONObjectWithData:data options:0 error:&error];

        dispatch_async(dispatch_get_main_queue(), ^{

            [self loadArray];

        });
}];