UICollectionView隐藏我的补充视图，为什么？

Question

So I'm creating a UISegmentedControl , which I am putting in a supplementary view for a collection view. I am then using that segmented control, through a delegate on it's IBAction , to set a BOOL type property on my UICollectionViewController , which appropriately changes the data being sent out from one stream to another. This all seems to work, as when I tap on the second tab after loading the collection view (which loads with the first tab selected, and the right data for the first tab), the right data shows up, but my supplementary view goes away!

What's odd is this:

 - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section

This method is properly being called, and I am properly setting the size of my supplementary view, and I can see so in my simulator, since my data is offset by the size of my supplementary view. What's NOT being called, though, is this method:

 - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath 

This method is only called when my collection view is loaded, thus loading the initial segmented controller, but is never called again, even though I am calling reloadData on the collectionView and the size method mentioned above is called again.

Now to add another twist, I went through and put a breakpoint in one of the methods for reloading the collection view, and did:

po [self.view recursiveDescription]

In the debugger, to find out if my segmented controller view is still there, and it is! It has it's hidden flag set to YES, though...

baseClass = UICollectionReusableView; frame = (0 0; 320 55); hidden = YES; layer = <CALayer: 0xef4bd30>

How do I get this view to not be hidden, when the only reference I have to it is in the method called:

 - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath

and this method isn't even being called this second time around?

Answer 1

So the answer has to do with FlowLayouts, and I wasn't properly setting mine up. I was indeed getting a size for my supplementary header, but I wasn't giving it attributes in the method:

- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath

Which is only called when you add a supplementary view to the attributes array in:

- (NSArray *) layoutAttributesForElementsInRect:(CGRect)rect 

Once I added an attribute for supplementary view of kind UICollectionElementKindSectionHeader, and the layout method was being called, then part of my troubles were abated.

Another problem was that I was checking index paths for sticky cells that I was trying to get to stick to the top of my collection view, and this index path checking collided with my supplementary view index path and was giving me trouble.

So to summarize: Make sure you are using the UICollectionViewFlowLayout methods! And make sure you don't have colliding index paths that remove your attributes from the attributes array.