TableViewController's Table View not displaying until the data is loaded

Question

I'm facing a strange issue. I have a method which populates an array with some data (fetchData) (quite a lot actually and it's a bit slow). I'm using the array to build the rows of the table.

I've tried calling fetchData in a number of places in my code, at various times in the construction of the view and I always seem to get the following: a black screen which is shown until the data from the array is loaded. I've called fetchData from the following:

• (void)viewDidLoad;
• (void)viewWillAppear:(BOOL)animated;
• (void)viewDidAppear:(BOOL)animated;

Since I'm using a navigation view controller, having the app appear to hang is pretty bad looking since it gets stuck on a black screen. What I was hoping my code would achieve was displaying an empty table, with a progress indicator until the data is loaded - then refresh. Unfortunately I'm not getting this far since the view isn't being loaded no matter where I call fetchData.

Help appreciated!

P.S. To get around this problem I even tried using a TTTableViewController, but the Loading view is never displayed. Typical. sigh

Answer 1

Your load method must be blocking the UI. You should move it to another thread and let the data load there. You can instantiate the thread in viewDidLoad.

This is a skeleton code for that you need to (using GCD)

dispatch_queue_t downloadQueue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(downloadQueue, ^{

    ... Move all the loading part here.

    dispatch_async(dispatch_get_main_queue(),^{
        ... Do all the UI updates, mostly, [tableView reloadData];
    })
})

Answer 2

It possible that you could add a timer to delay the call somewhere in your viewDidAppear method. For example:

- (void)viewDidAppear:(BOOL)animated {
    [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(fetchData) userInfo:nil repeats:NO];
}

This will give your app time to load the UI and start your loading screen, then start fetching the data later. You can also try fetching the data in a background thread if you would prefer to go that route

Answer 3

I was having the same issue with a table view not loading initially, but it worked n another .m file I had. Here is the one that worked:

add this to your viewDidLoad:

NSError *error = nil;
if (![[self fetchedResultsController] performFetch:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}

and this to the implementation block:

#pragma mark -
#pragma mark Fetched results controller

- (NSFetchedResultsController *)fetchedResultsController {

    if (fetchedResultsController == nil) {
        // Create the fetch request for the entity.
        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        // Edit the entity name as appropriate.
        NSEntityDescription *entity = [NSEntityDescription entityForName:@"OMFrackinG" inManagedObjectContext:managedObjectContext];
        [fetchRequest setEntity:entity];

// grouping and sorting optional

        //NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"country" ascending:YES];

        NSSortDescriptor *sortDescriptor1 = [[NSSortDescriptor alloc] initWithKey:@"state" ascending:YES];// was name

        NSSortDescriptor *sortDescriptor2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES];

        NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor1,sortDescriptor2, nil];

        [fetchRequest setSortDescriptors:sortDescriptors];
        propriate.

        NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:@"state" cacheName:nil];//@"state"
        aFetchedResultsController.delegate = self;
        self.fetchedResultsController = aFetchedResultsController;

        [aFetchedResultsController release];
        [fetchRequest release];
        [sortDescriptor1 release];
        [sortDescriptor2 release];
        [sortDescriptors release];
    }

    return fetchedResultsController;
}