ios - UICollectionView autosize height

Question

How do I properly resize a UICollectionView so that it fully displays its contents? I have tried many things, including setting its frame, calling reloadData and invalidating the layout:

self.collectionView.contentSize = CGSizeMake(300, 2000);
self.collectionView.frame = CGRectMake(0, 0, 300, 2000);
[self.collectionView reloadData];
[self.collectionView.collectionViewLayout invalidateLayout];

but none of this has any effect. After pressing the button I still see the initial view, like this:

I have a small demo program where I have a data source producing 100 elements. In Interface Builder I initially set the size of the UICollectionView to a small value so that not all elements fit, after that I press a button after which the code above is executed. I expect the UICollectionView to now show all elements, but it doesn't.

EDIT: The demo program can be found at https://github.com/mjdemilliano/TestUICollectionView.

EDIT2: I have observed that the frame update is lost at some point, because if I press the button again, the current frame is back to the old value. After adding some log statements in the button event handler, the log output is:

before: frame = {{0, 58}, {320, 331}}, contentSize = {320, 1190}
update button pressed
after: frame = {{0, 0}, {300, 2000}}, contentSize = {300, 2000}
before: frame = {{0, 58}, {320, 331}}, contentSize = {320, 1190}
update button pressed
after: frame = {{0, 0}, {300, 2000}}, contentSize = {300, 2000}

I don't understand why the frame change is not kept, what is changing it.

At some point I will replace the hardcoded values by values obtained from the flow layout, but I wanted to rule that out and keep my example as simple as possible.

Context: What I want to do eventually is the following: I have a scrollable view with various controls like labels and images, and a collection view with dynamic content. I want to scroll all that, not just the collection view, therefore I am not using the collection view's own scrolling facilities, which work fine.

Answer 1

I solved this eventually by fixing all Auto Layout issues, fixing the height of the collection view using a constraint. Then, whenever I know the content has changed I update the value of the constraint using the value collectionView.contentSize.height:

self.verticalLayoutConstraint.constant = self.collectionView.contentSize.height;

Then the collection view is resized properly and it behaves nicely within the overall scrollview. I have updated the GitHub test project with my changes.

To me, doing this by updating the constraint manually instead of being able to tell iOS: "make the frame height of the collection view as large as needed" does not feel right to me, but it's the best I have come up with so far. Please post a better answer if you have one.