UICollectionView Views Layer Priority - uicollectionview

Question

I'm seeing a very odd behavior with UICollectionViews.
Here is the scenario.
I have a UIViewController that has been pushed on to a UINavigationController stack.
The UIViewController view has nav bar and UICollectionView in grid layout. 3 cells wide by unlimited tall.
Just below extent of screen, I also have a UIToolbar hidden. The UIToolbar is on top of UICollectionView in layer hierarchy.
I then allow the user to put view in to "edit mode" and I animate UIToolbar on to the screen and covers bottom portion of UICollectionView. If user leaves "edit mode" I move UIToolbar back off screen.
While in "edit mode" I allow the user to multi select cells with check boxes that appear and uitoolbar has delete button.
Delete does the following:
- (void)deletePhotos:(id)sender {
if ([[self.selectedCells allKeys] count] > 0) {
[[DataManager instance] deletePhotosAtIndexes:[self.selectedCells allKeys]];
[self.selectedCells removeAllObjects];
[self.collectionview reloadData];
[self.collectionview performBatchUpdates:nil completion:nil];
}
}
// Data Manager method in singleton class:
- (void)deletePhotosAtIndexes:(NSArray *)indexes {
NSMutableIndexSet *indexesToDelete = [NSMutableIndexSet indexSet];
for (int i = 0; i < [indexes count]; i++) {
[indexesToDelete addIndex:[[indexes objectAtIndex:i] integerValue]];
NSString *filePath = [self.photosPath stringByAppendingPathComponent:[self.currentPhotos objectAtIndex:[[indexes objectAtIndex:i] integerValue]]];
NSString *thumbnailPath = [self.thumbPath stringByAppendingPathComponent:[self.currentPhotos objectAtIndex:[[indexes objectAtIndex:i] integerValue]]];
if ([[NSFileManager defaultManager] fileExistsAtPath: filePath]) {
[[NSFileManager defaultManager] removeItemAtPath: filePath error:NULL];
[[NSFileManager defaultManager] removeItemAtPath: thumbnailPath error:NULL];
}
}
[self.currentPhotos removeObjectsAtIndexes:indexesToDelete];
}
The data manager contains photo objects and are used in cell creation like so.
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
ImageCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"imageCell" forIndexPath:indexPath];
NSString *pngfile = [[[DataManager instance] thumbPath] stringByAppendingPathComponent:[[[DataManager instance] currentPhotos] objectAtIndex:indexPath.row]];
if ([[NSFileManager defaultManager] fileExistsAtPath:pngfile]) {
NSData *imageData = [NSData dataWithContentsOfFile:pngfile];
UIImage *img = [UIImage imageWithData:imageData];
[cell.imageView setImage:img];
}
if ([self.selectedCells objectForKey:[NSString stringWithFormat:#"%d", indexPath.row]] != nil) {
cell.checkbox.hidden = NO;
} else {
cell.checkbox.hidden = YES;
}
return cell;
}
So here is where I'm finding issues:
When deleting enough cells so that number of visible rows changes, UIToolbar is disappearing. In case of a full row of 3, if I only delete 1 or 2 items, the UIToolbar doesn't disappear. I am not doing any animation on the UIToolbar in delete method and only when hitting a Done button that ends edit mode. I've confirmed that this method isn't being called.
I've also confirmed that the UIToolbar isn't actually moving. If I add "self.collectionview removeFromSuperView" on hitting delete in cases where UIToolbar would normally disappear, the UIToolbar is exactly where expected on the screen. This gives me the impression the UICollectionView is somehow changing layer hierarchy in draw of parent view.
I've attempted trying to bringSubviewToFront for UIToolbar and sendSubviewToBack for collectionview and has no affect.
Re-iniating open toolbar causes uitoolbar to animate back in. Oddly, however, it seems to animate from below screen! This makes no sense unless the UICollectionView is somehow pushing the UIToolbar off the screen due after the point where I would be calling the removeFromSuperview call so I can't re-create.
One "solution" I have is to force the UIToolbar to come back in to position but without animation after a 0.01 second delay
[self performSelector:#selector(showToolbarNoAnimation) withObject:nil afterDelay:0.01];
This works.
Here is the question:
Any idea why UICollectionView causing this behavior to push UIToolbar offscreen after a full row is deleted? The hack works but doesn't explain the issue.
Thanks,
James

Answer 1

When you use auto layout, and your views are loaded from a storyboard (or xib), you can't set the frames of your views. Doing so may seem to work initially, but at some point auto layout will reset the view's frame based on the constraints, and you won't understand what happened, and then you'll post a question to stack overflow.
If you need to change the layout of a view, you need to update the view's constraints instead.
There is a constraint specifying the distance between the bottom edge of your toolbar and the bottom edge of its superview. Presumably that distance is -44 (where 44 is the height of the toolbar).
You need to connect that constraint to an outlet in your view controller. The outlet will have type NSLayoutConstraint *. Call it toolbarBottomEdgeConstraint.
When you want to animate the toolbar onto the screen, set constraint's constant to zero and call layoutIfNeeded in an animation block:
- (void)showToolbarAnimated {
[UIView animateWithDuration:0.25 animations:^{
self.toolbarBottomEdgeConstraint.constant = 0;
[self.toolbar layoutIfNeeded];
}];
}
To hide the toolbar, set the constraint's constant back to its original value:
- (void)hideToolbarAnimated {
[UIView animateWithDuration:0.25 animations:^{
self.toolbarBottomEdgeConstraint.constant = -toolbar.bounds.size.height;
[self.toolbar layoutIfNeeded];
}];
}