Asynchronous block in a loop

Question

How can I manage calling an asynchronous block in a loop?

My code to be called n-times:

- (void) convertToCountries:(NSString*)time longitude:(NSString*)lon latitude:(NSString*)lat {


CLLocation *myLocation = [[CLLocation alloc] initWithLatitude:[lat doubleValue] longitude:[lon doubleValue]];


[geocoder reverseGeocodeLocation:myLocation
               completionHandler:^(NSArray *placemarks, NSError *error) {
                   NSLog(@"reverseGeocodeLocation:completionHandler: Completion Handler called!");

                   if (error){
                       NSLog(@"Geocode failed with error: %@", error);
                       return;
                   }

                   if(placemarks && placemarks.count > 0)
                   {
                       //do something
                       CLPlacemark *topResult = [placemarks objectAtIndex:0];
                       NSString *addressTxt = [NSString stringWithFormat:@"%@, %@ %@,%@ %@", [topResult country],
                                               [topResult subThoroughfare],[topResult thoroughfare],
                                               [topResult locality], [topResult administrativeArea]];
                       NSLog(@"%@",addressTxt);

                       NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
                       [formatter setDateFormat:@"yyyy-MM-dd"];

                       //Optionally for time zone converstions
                       [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"..."]];


                       [DataOperations saveRecord:[topResult country] time:time];

                   }
               }];

}

I need to collect output data from these calls.

Any help will appreciated.

Since it is asynchronous call, it does not wait until the results are processed and then continue. The loop is done with just first parameters. — Vanya, Oct 10 '12 at 10:23
and what would you do instead? sequencing the calls (e.g., wait for one to complete, and use it results)? — sergio, Oct 10 '12 at 10:27
I am asking for the best approach regarding this situation. I have n records with latitude and longitude and those params are needed to be called with this function to get results for each record. I have done it recursively, but I do not like the solution. — Vanya, Oct 10 '12 at 10:30

score 1 · Accepted Answer · answered Oct 10 '12 at 12:29

Give your object a property, BOOL dunloadin.

Then, in the completion block, set self.dunloadin to YES.

Finally, your loop should look something like this:

for (int i=0; i<10; i++)
{
    self.dunloadin = NO;
    [self convertToCountries:…];

    while (!self.dunloadin)
    {
        [[NSRunLoop mainRunLoop] runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]];
    }
}

However, you might want to consider designing your app differently so that kludges like this aren't required.

Asynchronous block in a loop

1 Answers1