'NSInternalInconsistencyException', reason: 'Only run on the main thread!' error

Question

So I know the reason for this error, but I'm not really sure how to get around it.

I have a TextField that I want to not be editable, but with scrolling enabled inside a view.

This is how I set up that view:

    - (void)tableView:(UITableView *) tableView
didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
    NSDictionary *component = self.resultsTuples[indexPath.row];
    NSString* serverUrl = @"http://staging.toovia.com";
    NSString* pageLink = component[@"$element"][@"ContactCard"][@"PageLink"];
    NSString* recUrl =[NSString stringWithFormat:@"%@%@&format=json&fields=summary&fields=session_info", serverUrl,pageLink];

    [AJAXUtils getAsyncJsonWithUrl:(NSURL *)[NSURL URLWithString:recUrl]  callback:^(NSDictionary *returnjson){
        if (returnjson != nil){
            NSLog(@"RETURN JSON : %@", returnjson);
            NSString *userPageLink = returnjson[@"Node"][@"SessionInfo"][@"PostingAs"][@"Key"];
            self.detailController.userPageLink = userPageLink;
            self.detailController.nodePage = returnjson[@"Node"][@"Key"];
            NSString *selectedCard = component[@"$element"][@"Title"];
         //   [self.detailController setDescription:component[@"element"][@"ContactCard"][@"Description"]];
            [self.detailController setPageTitle:selectedCard];
            NSString* photoUrl = component[@"$element"][@"ContactCard"][@"Cover"][@"Medium"][@"Link"];
            [self.detailController setRestaurantImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:photoUrl]]]];



            self.detailController.title = selectedCard;

            NSString* rating = component[@"$element"][@"Summary"][@"AverageRating"];
            self.detailController.rating =(NSInteger)rating;
            [self.navigationController pushViewController:self.detailController animated:YES];
        }
    }];

This is the viewWillAppear code for the view:

-(void)viewWillAppear:(BOOL)animated{
    [super viewWillAppear: animated];
    self.rateView.notSelectedStar =[UIImage imageNamed:@"star-off.png"];
    self.rateView.fullSelectedStar = [UIImage imageNamed:@"star-on.png"];
    self.rateView.rating = self.rating;
    self.rateView.editable = YES;
    self.rateView.maxRating = 5;
    self.rateView.delegate = self;
    _pageTitleLabel.text = _pageTitle;
    _pageScoreLabel.text = _pageScore;
    _trendingImageView.image = [UIImage imageNamed:@"trending.png"];
    _restaurantImageView.image = _restaurantImage;

}

The full error is -

    2013-12-16 01:22:50.362 ReviewApp[7332:441f] *** Assertion failure in void _UIPerformResizeOfTextViewForTextContainer(NSLayoutManager *, UIView<NSTextContainerView> *, NSTextContainer *, NSUInteger)(), /SourceCache/UIFoundation_Sim/UIFoundation-258.1/UIFoundation/TextSystem/NSLayoutManager_Private.m:1510
2013-12-16 01:22:50.365 ReviewApp[7332:441f] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Only run on the main thread!'

So I guess it's happening because the resizing of the text field (when content is set) has to happen on the main thread. How do I force this to happen/suppress this error? I'm not in control of the text field resizing am I?

Thanks

Answer 1

I'm guessing that the callback from AJAXUtils happens on a background thread. I don't know if that is your code or not but you should do all UI operations (like setting text in a label, setting an image in an image view, pushing a view controller) on the main thread.

dispatch_sync(dispatch_get_main_queue(), ^{
    /* Do UI work here */
});

Answer 2

Swift 3.0 version

DispatchQueue.main.async(execute: {
    /* Do UI work here */
})

Answer 3

You must always perform UI code on the main thread. You are not, hence the error. Try this:

[AJAXUtils getAsyncJsonWithUrl:(NSURL *)[NSURL URLWithString:recUrl]  callback:^(NSDictionary *returnjson){
    if (returnjson != nil){
        NSLog(@"RETURN JSON : %@", returnjson);
        NSString *userPageLink = returnjson[@"Node"][@"SessionInfo"][@"PostingAs"][@"Key"];
        self.detailController.userPageLink = userPageLink;
        self.detailController.nodePage = returnjson[@"Node"][@"Key"];
        NSString *selectedCard = component[@"$element"][@"Title"];
     //   [self.detailController setDescription:component[@"element"][@"ContactCard"][@"Description"]];
        [self.detailController setPageTitle:selectedCard];
        NSString* photoUrl = component[@"$element"][@"ContactCard"][@"Cover"][@"Medium"][@"Link"];
        [self.detailController setRestaurantImage:[UIImage imageWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:photoUrl]]]];

        self.detailController.title = selectedCard;

        NSString* rating = component[@"$element"][@"Summary"][@"AverageRating"];
        self.detailController.rating =(NSInteger)rating;
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.navigationController pushViewController:self.detailController animated:YES];
        });
    }
}];

This ensures the display of the view controller is on the main thread. You may actually need to put a bit more of the code inside the call to dispatch_async.

Answer 4

Swift version

dispatch_async(dispatch_get_main_queue()){
      /* Do UI work here */
}

Answer 5

Also, it's not a very good way of doing things in didSelectRow. You should have a network layer, separate the network code from view controllers otherwise you will end up with huge view controller, code won't be testable.