Memory Warning-MapOverlay - ios

Question

I have question regarding memory usage of ios. I have implemented code as shown below and run it on the device about 10 min and it stopped and gave me warning "Received memory warning". I wonder why I am getting this warning.
NSArray *ants = [mapView overlays];
for(bb = 0; bb < [polygonArray count]; bb++){
int attr=[[idArray objectAtIndex:bb]floatValue];
coords = malloc(sizeof(CLLocationCoordinate2D) * [[polygonArray objectAtIndex:bb] count]);
for (int a = 0;a < [[polygonArray objectAtIndex:bb] count]; a++){
coords[a].latitude = [[[[polygonArray objectAtIndex:bb]objectAtIndex:a]objectAtIndex:0]doubleValue];
coords[a].longitude = [[[[polygonArray objectAtIndex:bb]objectAtIndex:a]objectAtIndex:1]doubleValue];
}
polygon = [[MKPolygon alloc]init];
polygon = [MKPolygon polygonWithCoordinates:coords count:[[polygonArray objectAtIndex:bb]count]];
//free(coords);
[previousPolygons addObject:polygon];
}
[mapView addOverlay:polygon];
}
}
[mapView removeOverlays:ants];

Answer 1

You seem to have more closing brackets that you have opening ones so there may be more at play than you've shown us, but I've shown what I think will improve your code below
NSArray *ants = [mapView overlays];
for(bb = 0; bb < [polygonArray count]; bb++){
int attr=[[idArray objectAtIndex:bb]floatValue];
coords = malloc(sizeof(CLLocationCoordinate2D) * [[polygonArray objectAtIndex:bb] count]);
for (int a = 0;a < [[polygonArray objectAtIndex:bb] count]; a++){
coords[a].latitude = [[[[polygonArray objectAtIndex:bb]objectAtIndex:a]objectAtIndex:0]doubleValue];
coords[a].longitude = [[[[polygonArray objectAtIndex:bb]objectAtIndex:a]objectAtIndex:1]doubleValue];
}
//Remove the next line because polygonWIthCoordinates creates one for you
//polygon = [[MKPolygon alloc]init];
polygon = [MKPolygon polygonWithCoordinates:coords count:[[polygonArray objectAtIndex:bb]count]];
//reinstate this line
free(coords);
[previousPolygons addObject:polygon];
}
//This is outside the for-loop so you'll only be adding the last polygon
[mapView addOverlay:polygon];
}
}
[mapView removeOverlays:ants];