问JSON序列化"Thread 1: signal SIGABRT“错误

EN

#import "ViewController.h"

@interface ViewController ()

@property (weak, nonatomic) IBOutlet UIButton *affichermeteo;
@property (weak, nonatomic) IBOutlet UILabel *meteo;

@end



@implementation ViewController


- (void)viewDidLoad {
    [super viewDidLoad];


}

- (IBAction)affichermeteo:(id)sender {

NSData *allCoursesData = [[NSData alloc] initWithContentsOfURL:
                              [NSURL     URLWithString:@"http://api.wunderground.com/api/e5cdee14984e242b/conditions/q/CA/San_Francisco.json"]];

NSError *error;

NSDictionary *allCourses = [NSJSONSerialization
                            JSONObjectWithData:allCoursesData
                            options:NSJSONReadingMutableContainers
                            error:&error];



if( error )
{
    NSLog(@"%@", [error localizedDescription]);
}
else {
    NSArray *currentobservation = allCourses[@"estimated"];
    for ( NSDictionary *theCourse in currentobservation )
    {
        _meteo.text=theCourse[@"weather"];

    }
}



}



@end