Objective c, how to wait until block finishes?

Question

Objective-C

There is a function that should return an array either from a file or download from the server and put it in this file. I ask this function to return an array, it returns an empty one, and after that it executes a request to the server, how to return data after downloading from the server?
Roughly what I have:

-(NSArray*)getData{
  __block NSArray *returnData = nil;
  if([self internetConnect]){
     [self reloadData:^(NSArray* loadData){
       returnData = loadData;
     }];
  }else{
     //тут проблем нет
  }
  return returnData;
}

The reload data method also has a block that loads data, in general, I think like this block with a block that all in a compartment load data and put it in an array, return from this getData method after everything has loaded.
Thanks in advance for your help.

Answer 1

You want the current thread to wait for the asynchronous request to complete.

-(NSArray*)getData{
    __block NSArray *returnData = nil;
    if([self internetConnect]){
        dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^(void){
            [self reloadData:^(NSArray* loadData){
                returnData = loadData;
            }];
        });
    }else{
        
    }
    return returnData;
}

You can also create your own competitive queue

+(dispatch_queue_t)sharedConcurrentQueue {
    static dispatch_queue_t queue = nil;
    static dispatch_once_t onceToken = 0;
    
    dispatch_once(&onceToken, ^{
        queue = dispatch_queue_create("MyQueueName", DISPATCH_QUEUE_CONCURRENT);
    });

    return queue;
}

And put any tasks in it in this way

-(void)testFunc {
    dispatch_async([MyClass sharedConcurrentQueue], ^(void){
        // Все, что хотим запустить и идти дальше, не дожидаясь
    });
    
    dispatch_sync([MyClass sharedConcurrentQueue], ^(void){
        // Все, что хотим запустить и подождать завершения
    });
}

You can read about it here .
Or google "Grand Central Dispatch".