Views not updating when wanted

[sleaver]

I'm working on an RSS reader and I want to show a transparent modal view while the feed is updating before the next view containing all the feed items and here is the code:

PHP Code:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    // Load the transparent loading modal view
    loadingView = [LoadingView loadingViewInView:[self.view.window.subviews objectAtIndex:0]];
    
    // Navigation logic may go here. Create and push another view controller.
    FeedInfo *feed = (FeedInfo *)[eventsArray objectAtIndex:indexPath.row];    
    [self showFeed:feed animated:YES];
    [feed release];
} 


PHP Code:

- (void)showFeed:(FeedInfo *)feed animated:(BOOL)animated {
    // Create a detail view controller, set the recipe, then push it.
    FeedDetailListTableViewController *feedDetailViewController = [[FeedDetailListTableViewController alloc] initWithNibName:@"FeedDetailListTableView" bundle:nil];
    feedDetailViewController.feed = feed;
    
    // Get feed items
    [UIApplication sharedApplication].networkActivityIndicatorVisible = YES;
    FeedHandler *fh = [[FeedHandler alloc] init];
    fh.feed = feed;
    [fh RefreshFeed:feed.link];
    [fh release];
    
    // Remove the loading view
    [loadingView performSelector:@selector(removeView) withObject:nil];
    
    // Display view controller
    [self.navigationController pushViewController:feedDetailViewController animated:animated];
    [feedDetailViewController release];
} 


The problem is that the loadingView does not display until the feedDetailViewController is pushed. I know this because if I comment out the line removing the window it will display as soon as the feedDetailViewController view is pushed. The loadingView doesn't need pushing as it's not done in the example I got this from and it wouldn't show when the remove line is commented out.

I have also ran into this problem with my custom UITableViewCell, I can add/change/remove items in the cell

PHP Code:

if (selected) { } 


using

PHP Code:

- (void)setSelected:(BOOL)selected animated:(BOOL)animated 


But the changes can't be seen until the next view controller is pushed on to the UINavigationController. You can imaging they pretty much disappear as soon as they are shown.

So, do you know why this may be happening? If so I would appreciate any ideas on how this can be solved!

Thanks

[Duncan C]

Originally Posted by sleaver

I'm working on an RSS reader and I want to show a transparent modal view while the feed is updating before the next view containing all the feed items.
<snip>
The problem is that the loadingView does not display until the feedDetailViewController is pushed. I know this because if I comment out the line removing the window it will display as soon as the feedDetailViewController view is pushed. The loadingView doesn't need pushing as it's not done in the example I got this from and it wouldn't show when the remove line is commented out.

I have also ran into this problem with my custom UITableViewCell, I can add/change/remove items in the cell

PHP Code:

if (selected) { } 


using

PHP Code:

- (void)setSelected:(BOOL)selected animated:(BOOL)animated 


But the changes can't be seen until the next view controller is pushed on to the UINavigationController. You can imaging they pretty much disappear as soon as they are shown.

So, do you know why this may be happening? If so I would appreciate any ideas on how this can be solved!

Thanks

I don't completely follow your sample code, but bet I know what the issue is anyway.

In iOS (and Mac OS) UI changes don't take place until you revisit the event loop. If you add a view, change a highlight flag, or whatever, you have to return from your method and let the system trigger a draw event before you see the results on the screen.

If you do a bunch of stuff, then push a view controller, THEN return, you won't get a chance to see the changes, because you haven't returned until after you push the view controller.

If you need the UI to update, you can use a method

performSelector:withObject:afterDelay:

You might do something like this:


//set a table view cell to selected (or whatever UI change)
[self performSelector: pushNewView withObject: nil afterDelay: 0];


You would then write a function pushNewView that actually pushed the new view controller. That method would get called after the system re-visited the main event loop and handled the drawing you requested.

performSelector:withObject:afterDelay: allows the system to return to the main event loop even if the delay value is zero.

[sleaver]

Originally Posted by Duncan C

I don't completely follow your sample code, but bet I know what the issue is anyway.

In iOS (and Mac OS) UI changes don't take place until you revisit the event loop. If you add a view, change a highlight flag, or whatever, you have to return from your method and let the system trigger a draw event before you see the results on the screen.

If you do a bunch of stuff, then push a view controller, THEN return, you won't get a chance to see the changes, because you haven't returned until after you push the view controller.

If you need the UI to update, you can use a method

performSelector:withObject:afterDelay:

You might do something like this:


//set a table view cell to selected (or whatever UI change)
[self performSelector: pushNewView withObject: nil afterDelay: 0];


You would then write a function pushNewView that actually pushed the new view controller. That method would get called after the system re-visited the main event loop and handled the drawing you requested.

performSelector:withObject:afterDelay: allows the system to return to the main event loop even if the delay value is zero.

Thanks for the reply.

After more researching that is pretty much the same conclusion I came too but I went the route of NSThread. Is that the right way or should I just use a plain function?

Probably a dumb question but why does a delay of 0 all the eventLoop revisit?

[Duncan C]

Originally Posted by sleaver

Thanks for the reply.

After more researching that is pretty much the same conclusion I came too but I went the route of NSThread. Is that the right way or should I just use a plain function?

Probably a dumb question but why does a delay of 0 all the eventLoop revisit?

NSThreads will work too, but NSOperationQueues are easier to use.

The performSelector:withObject:afterDelay queues up a request to do a performSelector call later. The call doesn't get queued until the next pass through the event loop, even if the delay is zero.