Adding subViews on non-main Thread not displaying

Question

I create a UIView contentView and display it. I then fetch data from server and create a bunch of subviews displaying the data. I am using MBProgressHUD to display while waiting on data.

if (datasetSubBar.panels == nil) {
    MBProgressHUD *HUD = [MBProgressHUD showHUDAddedTo:datasetSubBar.filterListView animated:YES];

    HUD.labelText = @"Creating Panels";

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
        [datasetSubBar createPanels];

        dispatch_async(dispatch_get_main_queue(), ^{
            [MBProgressHUD hideHUDForView:datasetSubBar.filterListView animated:YES];
        });
    });
}

in createPanels method, i fetch the data then create the panels. The panel is created, added to filterListView (the content view) and then add the constraints:

for (int i = 0; i < panels.count; i++) {
    NSLog(@"thread: %@", [NSThread currentThread]);

    NSDate *startDate = [NSDate date];

    DatasetFilterListPanelView *panel = [panels objectAtIndex:i];

    [contentView addSubview:panel];

    // add constraints to position each panel
}

these are run on a separate thread which is what I believe the issue is. The UI can only be updated on the main thread.

I tried adding:

dispatch_async(dispatch_get_main_queue(), ^{
    [contentView addSubview:panel];
});

But that raises errors for the constraints (the constraints don't have reference to it since its in a different thread).

If I run createPanels on the main thread, the panels will display but it also locks up the UI until its complete.

Any ideas?

How many panels are you adding that it's overwhelming the main thread? Maybe a UITableView and cell would be better than "panel" views because they are lazy loaded? — Jason Harwig, Feb 28 '13 at 20:11
table view would be nice, but they are 2 columns in portrait and 3 columns in landscape. We want to be able to use as much as the screen as we can — Padin215, Feb 28 '13 at 20:40
Have you tried adding the constraints inside the same block as `[contentView addSubView:panel]`? — Mike D, Feb 28 '13 at 20:43
The constraints are not the issue, they are not being displayed/showed. When i look at the list of panels, their frame show correct points and sizes. They are where they should be in the contentView. — Padin215, Feb 28 '13 at 20:54
"they are 2 columns in portrait and 3 columns in landscape" - what about using UICollectionView? It's more flexible than table view but still gives you all the lazy loading/reuse benefits. — jsd, Feb 28 '13 at 22:31
@jsd: Thanks for the suggestion, I'm testing it out. Running into performance issues from loading the panel on demand with it though, seems my panel isn't very optimal: http://stackoverflow.com/questions/15163693/creating-a-uicollectionviewcell-with-uiimage-and-uilabels-creates-slow-scrolling — Padin215, Mar 01 '13 at 17:55
I did end up converting it to UICollectionView instead of my own creation. — Padin215, Mar 05 '13 at 19:58

score 0 · Answer 1 · answered Feb 28 '13 at 20:34

0

I'm not sure which constraints are violated, but you could also try:

[contentView performSelctorOnMainThread:@selector(addSubview) withObject:panel waitUntilDone:YES];

instead of

dispatch_async(dispatch_get_main_queue(), ^{
    [contentView addSubview:panel];
});

Not sure whether this will help.

answered Feb 28 '13 at 20:34

Nils Ziehn

4,118
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40

No constraints are violated, iOS doesn't try to break any to make the views fit. – Padin215 Feb 28 '13 at 20:41

Adding subViews on non-main Thread not displaying

1 Answers1