Question

Im developing an IOS 5 app which takes a feed from a url and displays the posts in a tableview. I have a View controller that loads the table cells with the posts in the feed. This all works perfectly.

However, i wanted to use the SVProgressHUD to show whilst the feed is being loaded in a separate thread.

So in my -(void)viewDidLoad method I have the following:

- (void)viewDidLoad
{
    [super viewDidLoad];
    [SVProgressHUD showInView:self.view status:@"loading.." networkIndicator:YES];
    dispatch_async(kBgQueue, ^{NSData* data = [NSData dataWithContentsOfURL: latestFeedURL];
    [self performSelectorOnMainThread:@selector(fetchedData:) withObject:data waitUntilDone:YES];});

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(foregroundRefresh:) name:UIApplicationWillEnterForegroundNotification object:nil];

    self.pull = [[PullToRefreshView alloc] initWithScrollView:(UIScrollView *) self.feedTableView];
    [self.pull setDelegate:self];
    [self.feedTableView addSubview:self.pull];

    self.title = @"Latest";
}

- (void)fetchedData:(NSData *)responseData {
    //parse out the json data
    NSError* error;
    NSDictionary* json = [NSJSONSerialization JSONObjectWithData:responseData options:kNilOptions error:&error];

    NSMutableArray* latestFeed = [json objectForKey:@"posts"]; //2

    self.feedUpLoads = latestFeed; 
    NSLog(@"objects: %@", latestFeed); //3
    [self.feedTableView reloadData];
    [SVProgressHUD dismiss];
}

This all works fine, im getting the data which is loaded in a background thread and my table is displaying the posts with all the detail required. The problem I have is that the SVProgressHUD is not showing at all. Even if I put the [SVProgressHUD showInView line in the fetchData method, it’s still not showing. (by the way i know the SVProgressHUD code works because I can actually make it show forexample in the viewWillAppear method.

Im guessing that it’s not working because at the point when I’m calling it the view does not yet fully exist? But if that’s the case where should I call it so that it shows whilst the feed is being called and where should I remove it?

Any help appreciated! thanks in advance!!

Answer 1

For anyone else having a similar problem, this can also happen because you have a long loop or a piece of code that takes a long time to execute. If this happens, your progress bar wont be shown until after the loop, which kind of defeats the purpose.

To solve this issue you need to you this:

• (void)performSelectorInBackground:(SEL)aSelector withObject:(id)arg

Basically your code would look something like this:

- (IBAction)submitPost:(id)sender {
    //now we show the loading bar and submit the comment
    [SVProgressHUD showWithStatus:@"Submitting post" maskType:SVProgressHUDMaskTypeGradient];
    SEL aSelector = @selector(submitDataOfPost);
    [self performSelectorInBackground:aSelector withObject:sender];
}

This will basically load the progress bar, and in a background thread, the method you want to execute will be called. This makes sure that the UI is updated (shows the progress hud) at the same time that your code is executed.