UIActivityMonitor Out of Sync - uitableview

Question

I have reviewed many different ways to get the activity indicator to start however I feel synchronising it correctly seems a bit challenging. Nothing is broken with the below code however the Activity monitor icon(throbber) doesn't show up until the last moment before transitioning to the next view.
When the user taps the one of the elements within the UITable it kicks off getting a JSON response then takes the user to the next View. Works perfectly. Except the ActivityIndicator is late to show up as stated before.
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
UIActivityIndicatorView *spinner = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
spinner.frame = CGRectMake(0, 0, 24, 24);
UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
cell.accessoryView = spinner;
[spinner startAnimating];
timer = [NSTimer scheduledTimerWithTimeInterval:3.0/1.0 target:self selector:#selector(loading) userInfo:nil repeats:YES];
//Go to the next view
if ([cell.textLabel.text isEqualToString:#"Vatsim Pilots"]) {
VatsimViewController *detail = [self.storyboard instantiateViewControllerWithIdentifier:#"newview"];
[self.navigationController pushViewController:detail animated:YES];
}
}
I have attempted to use the NSStimer function but clearly that doesn't work. I have seen others do this but not hitting a JSON service. I would have thought it wouldn't matter where the data is coming from and only cares when the data is ready.
Thanks in advance!

Answer 1

The problem is that the spinner doesn't start spinning until after the current CATransaction ends - after all your code has finished. But your code doesn't finish until the JSON response comes back, because (in code apparently not shown here) you do this interaction synchronously.
Don't. You should not be networking synchronously! You are blocking the main thread when you do that - and if you do that for too long, the WatchDog process will kill your app dead.
Thus the fact that the spinner doesn't start is actually symptomatic of something much deeper that you're doing wrong.
Having said that, the solution to your problem is to start the spinner spinning and then immediately get off the main thread, so that the CATransaction has a chance to end. The spinner will then actually start spinning! Then when your code re-enters you can start your time-consuming navigation, as in this code (from my book):
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
// ... start spinner here ...
// now get off main thread
double delayInSeconds = 0.1;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
// ... now do time-consuming stuff ...
// ... and finally, navigate:
UIViewController *detailViewController = [ViewController new];
[self.navigationController pushViewController:detailViewController animated:YES];
});
}