UICollectionView in embedded view controller does NOT call cellForItemAtIndexPath - ios

Question

I have 2 view controllers embedded in a view vertically. View controller A (uploader), and B (docList).
B contains a UICollectionView
All, methods except cellForItemAtIndexPath inside the datasource of the collection view get called correctly, and i double checked everything. There is 1 section. There are more than 0 rows. The size of the rows I return is smaller than the collection view, etc
Here's a diagram to illustrate the setup:
My issue is:
Unless i turn on setTranslatesAutoresizingMaskIntoConstraints to YES, cellForItemAtIndexPath will never be called. If i set that property to YES on the View Controller B's view, then it does get called. But the layout is then screwed up, because I am not using springs and struts. We only use constraints here.
Do you know what i can be doing wrong when embedding the view controller that contains the UICollectionView?
Here is the code that embeds the two view controllers' views, and sets them as child controllers:
- (MFFormBaseCell *)cellForComponent
{
self.cell = [[MFFormBaseCell alloc] initWithFrame:CGRectZero];
[self.cell addSubview: uploader.view];
[self.cell addSubview: docList.view];
UIView* uploaderView = uploader.view;
UIView* docListView = docList.view;
NSMutableArray* tempConstraints = [[NSMutableArray alloc]init];
[tempConstraints addObjectsFromArray:
[NSLayoutConstraint constraintsWithVisualFormat: #"V:|-8-[uploaderView]-1-[docListView]-8-|"
options: NSLayoutFormatDirectionLeadingToTrailing metrics:nil
views: NSDictionaryOfVariableBindings(uploaderView, docListView)]];
[tempConstraints addObjectsFromArray:
[NSLayoutConstraint constraintsWithVisualFormat: #"H:|-[uploaderView]-|"
options: NSLayoutFormatDirectionLeadingToTrailing metrics:nil
views: NSDictionaryOfVariableBindings(uploaderView)]];
[tempConstraints addObjectsFromArray:
[NSLayoutConstraint constraintsWithVisualFormat: #"H:|-[docListView]|"
options: NSLayoutFormatDirectionLeadingToTrailing metrics:nil
views: NSDictionaryOfVariableBindings(docListView)]];
uploaderConstraints = [tempConstraints copy];
[self.cell addConstraints: uploaderConstraints];
[self.embedder addChildViewController:uploader];
[uploader didMoveToParentViewController:self.embedder];
[self.embedder addChildViewController:docList];
[docList didMoveToParentViewController:self.embedder];
docList.view.frame = self.cell.bounds;
return self.cell;
}
And here is the code from View Controller B, that sets up the UICollectionView and a vertical flow layout for it.
- (void)modelDidLoad
{
_dataSource = [[MFCardDataSource alloc] initWithData: self.cardModel];;
UICollectionViewFlowLayout *aFlowLayout = [[UICollectionViewFlowLayout alloc] init];
[aFlowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
_collectionView = [[UICollectionView alloc] initWithFrame:self.view.frame collectionViewLayout:aFlowLayout];
[_collectionView setDelegate: self];
[_collectionView setDataSource:_dataSource];
[_collectionView setBackgroundColor:[UIColor clearColor]];
for (NSString* type in [MFCardCollectionModel typeArray])
[_collectionView registerClass:[MFImageCard class] forCellWithReuseIdentifier: type];
[_collectionView setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:_collectionView];
[self registerConstraintsForView:_collectionView];
if ([self respondsToSelector:#selector(edgesForExtendedLayout)])
self.edgesForExtendedLayout = UIRectEdgeNone;
[super modelDidLoad];
}
And the contents of registerConstraintsForView:
-(void) registerConstraintsForView:(UIView*)collectionView
{
NSDictionary* metrics = #{ #"padding": #PADDING };
NSDictionary* views = NSDictionaryOfVariableBindings(_collectionView);
[self.view addConstraints:[NSLayoutConstraint
constraintsWithVisualFormat:#"V:|-padding-[_collectionView]-padding-|"
options:NSLayoutFormatDirectionLeadingToTrailing
metrics:metrics
views:views]];
[self.view addConstraints:[NSLayoutConstraint
constraintsWithVisualFormat:#"H:|-padding-[_collectionView]-padding-|"
options:NSLayoutFormatDirectionLeadingToTrailing
metrics:metrics
views:views]];
}

Answer 1

I got around the problem by Subclassing UICollectionView, and using the subclass instead.
On the subclass I overrode 2 methods:
- (void) setContentSize:(CGSize)contentSize
{
CGSize origSize = self.contentSize;
[super setContentSize:contentSize];
if (!CGSizeEqualToSize(contentSize, origSize))
{
[self invalidateIntrinsicContentSize];
}
}
- (CGSize) intrinsicContentSize
{
return CGSizeMake(UIViewNoIntrinsicMetric, self.contentSize.height);
}
Then, i have a method inside my view controller which contains the Collection View, which calculates the required Height needed for the collection view.
I then call setContentSize with the calculated height on my subclass of Collection View, and that makes sure that it returns an intrinsicContentSize as tall as it needs to be to show all the card records inside it.