I have a stack view that contains three UICollectionViews, set up to give each of them equal vertical space. That stack view is set to be the height of half of the display, so that it uses more space on larger devices. This has been set up in Interface Builder.
So, I need to set the cell size of the UICollectionView at runtime, since until we are running, I don't know what the actual size of the cells will be. I want them to be square, so I just want to take into account the height of the UICollectionView, subtract out the top and bottom section insets, and set the itemSize to the resulting size.
I attempt to do this in viewDidLayoutSubviews, since by then I figure that the initial heights of the collection views have been set. However, they appear to be set to 1000x1000 (even though they are a much more reasonable size in the storyboard), and so I compute a cell size based on a collection view height of 1000. This is too large, but I figure that I'll get called again and get another chance to recompute it. And I do, but not before UICollectionView complains loudly that the itemSize is incorrect (ie. too large to fit in the collectionView, which now has the "correct" size.)
What is the best way to get the behavior I'm looking for without the warnings from UICollectionView? Setting the collection view item size at runtime based on the eventual size of the UICollectionView is something I've struggled with in the past, and there never seems to be the "right" time to set the itemSize. I don't want to dynamically return it, if only because it's not something that changes during the life of the program. There just seems to be some inconsistencies that occur when laying out the views initially.
It seems odd to me that the collection view comes in with an initial size of 1000.0 by 1000.0, but I'm not sure how or why to fix that - perhaps it has something to do with being embedded in a stack view?
Edited to add: It is almost certainly the UIStackView that is causing the layout issues. I created a dummy project to test the size of a UICollectionView when it is the top level view vs embedded in a UIStackView. If it is not embedded, when viewDidLayoutSubviews is called, it has been properly sized to fit the bounds of its superview. However, if it is inside of a UIStackView, it stays at the default size of 1000x1000.
For now, I am working around this problem by adding the following code in viewDidLayoutSubviews:
if collectionView.bounds.size.width > view.bounds.size.width { view.layoutIfNeeded() }
Where collectionView is inside a UIStackView and view is the main view of the UIViewController. This allows all subsequent calculations based on the size of the view to be correct, and hopefully will not get called if the UIStackView behavior ever gets fixed.
Similar discussions here and here. Interesting point that in XCode8, the new default is to not save sizes of views in the XIB file, but instead bring everything in with an initial size of 1000x1000, to be resolved during the first layout pass. Except for UIStackViews, I guess.
