Specific part of code not being executed in iOS - ios

Question

I am retrieving data from Parse.com and try to add an image with this data to an array. However, some code is not being executed without any obvious reason. This is the code:
PFQuery *userQuery = [PFUser query];
[userQuery whereKey:#"objectId" containedIn:[self.event objectForKey:#"members"]];
[userQuery findObjectsInBackgroundWithBlock:^(NSArray *users, NSError *error) {
if (!error) {
self.membersArray = [NSMutableArray arrayWithArray:users];
[self.tableView reloadData];
for (PFUser *user in self.membersArray) {
[self.memberPhotosArray addObject:[NSNull null]];
NSInteger index = [self.memberPhotosArray indexOfObject:user];
PFFile *photoFile = [user objectForKey:#"profilePicture"];
[photoFile getDataInBackgroundWithBlock:^(NSData *result, NSError *error) {
if (!error) {
NSLog(#"Before creating image");
UIImage *image = [UIImage imageWithData:result];
[self.memberPhotosArray[index] addObject:image];
NSLog(#"After creating image");
[self.tableView reloadData];
}
}];
}
}
}];
The first log is being executed, everything after this line is not being called. Can someone explain why and provide a solution?

Answer 1

Looks like your code is running on a background thread. Run the code in the final callback block on the main thread.
if (!error) {
NSLog(#"Before creating image");
UIImage *image = [UIImage imageWithData:result];
dispatch_async(dispatch_get_main_queue(), ^{
[self.memberPhotosArray[index] addObject:image];
NSLog(#"After creating image");
[self.tableView reloadData];
});
}
UI related operations should only be performed on the main thread.