NSURLConnection sendSynchronousRequest - background to foreground

UIImage *image = [self.imgCache objectForKey:urlString];
if(!image){
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:urlString] cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:60.0];


    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        NSURLResponse *response = nil;
        NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil];
        NSLog(@"%@",response);
        UIImage *img = [UIImage imageWithData:data];
        //

        if(img)
        {
            dispatch_sync(dispatch_get_main_queue(), ^{
                [self.imgCache setObject:img forKey:urlString];
                completionBlock(img);
            });
        }
    });

}
else{
    completionBlock(image);
}

callback method

MainView Controller:

.h file

#import "callbackcontroller.h"

@interface EventListViewController : UIViewController <EventCallbackDelegate>

.m file

CreateEventViewController * next = [[CreateEventViewController alloc]init];

next.delegate = self;

[self presentViewController: next animated:YES completion:nil];

//Callback Method Function

-(void)refreshviewevent{

NSLog(@"Do your code");

}

CallBack ViewController

.h file

@protocol EventCallbackDelegate <NSObject>

-(void)refreshviewevent;

@end

@interface CreateEventViewController : UIViewController

@property (strong,nonatomic) id <EventCallbackDelegate> delegate;

@end

.m file

//put callback place

[self.delegate refreshviewevent];

NSMutableArray convert into Json data

NSMutableArray *allObjectArray = [[NSMutableArray alloc]init];

 [allObjectArray addObject:@"any value"];

 NSError *error;

 NSData *json_Data = [NSJSONSerialization dataWithJSONObject:allObjectArray

                                                                           options:NSJSONWritingPrettyPrinted

                                                                             error:&error];

  id jsonObject = [NSJSONSerialization JSONObjectWithData:json_Data options:NSJSONReadingMutableContainers error:nil];