Navigating in UITableView Slow with JSON Issue - iphone

Question

I am loading 4 cities string in the table view which is working but when I select one of the cell and navigate to the other table it navigate too slow. I am using the same code below in the the other table with different link. Could you please tell me why it takes long time (~4 - 6 Sec) to get to the other view?
- (void)viewDidLoad
{
[super viewDidLoad];
NSURL * url = [NSURL URLWithString:#"http://kalkatawi.com/jsonTest.php"];
NSData * data = [NSData dataWithContentsOfURL:url];
NSError *e = nil;
jsonArray = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&e];
jsonArray1 = [[NSMutableArray alloc] init];
for(int i=0;i<[jsonArray count];i++)
{
NSString * city = [[jsonArray objectAtIndex:i] objectForKey:#"city"];
[jsonArray1 addObject:city];
}
-
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
NSString *tempString = [jsonArray1 objectAtIndex:indexPath.row];
cell.textLabel.text = tempString;
return cell;
}
-
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
SeconfViewController *second = [[SeconfViewController alloc] initWithNibName:#"SeconfViewController" bundle:nil];
UITableViewCell *selectedCell = [tableView cellForRowAtIndexPath:indexPath];
NSString *cellText = selectedCell.textLabel.text;
NSString *edit = [NSString stringWithFormat:#"http://kalkatawi.com/jsonTest.php?d=1&il=%#", cellText];
second.str2 = edit;
[self.navigationController pushViewController:second animated:YES];
}

Answer 1

It takes more time to navigate on the other screen because you are synchronously loading the data from the server. In iOS all the UI is done on the main thread, and by making your data call on the main thread you are blocking it. The best way I know to handle this is to use GCD (Grand Central Dispatch). It's an API in iOS that will spawn threads for you without a hassle. You just need to tell that you want to make the call to load data from the server on a background thread. When you do that, view should navigate instantaneously. You can use an Activity indicator while the data comes.
dispatch_async(dataQueue, ^{
// Load all your data here
dispatch_async(dispatch_get_main_queue(), ^{
// Update the UI
});
});

Answer 2

Maybe because you are downloading synchronous and you are blocking the main thread maybe that is the reason that your app freeze for 4-6 sec, try to download your json asynchronous
- (void)viewDidLoad
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
NSData *response = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:#"http://kalkatawi.com/jsonTest.php"]];
NSError *parseError = nil;
jsonArray = [NSJSONSerialization JSONObjectWithData:response options:NSJSONReadingAllowFragments error:&parseError];
jsonArray1 = [[NSMutableArray alloc] init]
for(int i=0;i<[jsonArray count];i++)
{
NSString * city = [[jsonArray objectAtIndex:i] objectForKey:#"city"];
[jsonArray1 addObject:city];
}
}
dispatch_sync(dispatch_get_main_queue(), ^{
[self.myTableView reloadData];
});
});
}