Data not loading in UITableView after parsing in background

Question

I'm trying to implement an activity indicator when I parse my XML data.

I found this Activity indicator (spinner) with UIActivityIndicatorView and have it working. However, because I'm using performSelectorInBackground when it finishes parsing none of the data shows up in my tableview.

I have tried [self.tableview reloadData] and I've tried [self.view setNeedsDisplay] however, nothing seems to work.

If I leave the view and come back to it, all the data appears in the tableview cells.

Any ideas?

What have you tried? How are you adding the data to the table view? Can you show all related code? — KerrM, Dec 08 '14 at 15:51
@KerrM All my parsing and retrieving the RSS Feed occur in a file that I import into my view controller. In my view controller, I do this: `self.rssNews = [[ParseRSSNews alloc] initWithUrl:self.url];` In initWithUrl method in the parser file, I did this: `[self performSelectorInBackground:@selector(parseXMLFileAtURL:) withObject:url];` Once it is done parsing, I did: `[self performSelectorOnMainThread:@selector(doneParsing) withObject:nil waitUntilDone:NO];` when I print out how many items are in my self.rssNews (in view controller), that it shows 0. So, it's not returning the data. — Sandy D., Dec 08 '14 at 16:02
As mentioned, you need to call reloadData on the *main thread*. — emma ray, Dec 08 '14 at 16:43

Boris Charpentier · Accepted Answer · 2014-12-08T16:28:45.717

1

You should call

[self.tableview reloadData]

in the main thread (you can check in wich thread you'r in with [NSThread isMainThread])

you can do

[UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
//create background queue
dispatch_queue_t backgroundQueue = dispatch_queue_create("com.mycompany.myqueue", 0);
//dispatch in background
dispatch_async(backgroundQueue, ^{
        //execute long operation in background thread
        self.rssNews = [[ParseRSSNews alloc] initWithUrl:self.url];
    //dispatch in main thread after long operation is finish
    dispatch_async(dispatch_get_main_queue(), ^{  [self.tableView reloadData]; });
});

edited Dec 08 '14 at 16:28

answered Dec 08 '14 at 15:53

Boris Charpentier

3,515
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28

Since my parsing and retrieving the RSS feed occur in a separate file, I don't have access to self.tableview. I was able to do this in my view controller: `[UIApplication sharedApplication].networkActivityIndicatorVisible = YES; dispatch_async(dispatch_get_main_queue(), ^{ self.rssNews = [[ParseRSSNews alloc] initWithUrl:self.url]; [self.tableView reloadData]; });` However, the network indicator doesn't go while it's parsing. – Sandy D. Dec 08 '14 at 16:22
Thank you Boris!! This helped a LOT!!! I also added to turn off the networkActivityIndicatorVisible within the second dispatch_async(). Again, Appreciate all of your help!!! =) – Sandy D. Dec 08 '14 at 18:05
I'm guessing I would need to release the dispatch queue? I tried doing this in dealloc, `dispatch_release(backgroundQueue);` but Xcode says ARC forbids explicit message send of release -- so I guess ARC will handle releasing the dispatch queue and I shouldn't have to do anything for that? – Sandy D. Dec 08 '14 at 18:17
1

Found the answer: `If your deployment target is iOS 6.0 or Mac OS X 10.8 or later ARC will manage your queue for you. You do not need to (and cannot) use dispatch_retain or dispatch_release if ARC is enabled.` Reference: http://stackoverflow.com/questions/8618632/does-arc-support-dispatch-queues – Sandy D. Dec 08 '14 at 18:22

Data not loading in UITableView after parsing in background

1 Answers1