UICollectionView doesn't contain UICollectionViewCell in IB - xcode

Question

I'm trying to add a UICollectionView to a .nib file in IB. I've worked through a few tutorials and had no problems.
In my existing app, when I drag a collection view into a view in IB and then expand the object, the CollectionView Flow Layout is there , but there is no collection view cell. I also cannot drag and drop a cell into the collection view. Also the collection view is displayed differently, showing an image of a grid of cells instead of the normal white box.
I've tried creating a new view controller with nib, and have the same results when adding a collectionView.
This app WAS targeting iOS 4.2, but I've changed the deployment target to iOS 6.
In any newly created projects I don't get this behavior.

Answer 1

I can't tell you why it does not work, but for me the subclass approach from this blog post solved the problem:
http://www.adoptioncurve.net/archives/2012/09/a-simple-uicollectionview-tutorial.php
here is a short summary:
create a new class MyViewCell which extends UICollectionViewCell and create properties, actions, outlets and methods as needed.
#interface MyViewCell : UICollectionViewCell
create a View (xib file) with a Collection View Cell as its root object (and delete the object which is created by default).
in the attributes set the custom class of this Collection View Cell to your extended class MyViewCell (instead of the default UICollectionViewCell).
in the attributes under Collection Reusable View define an Identifier, e.g. myCell, you will need this later to register your call.
go back to your custom class and modify the inithWithFrame method to load and use your created view.
- (id)initWithFrame:(CGRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
// Initialization code
NSArray *arrayOfViews = [[NSBundle mainBundle] loadNibNamed:#"CVCell" owner:self options:nil];
if ([arrayOfViews count] < 1) { return nil; }
if (![[arrayOfViews objectAtIndex:0] isKindOfClass:[UICollectionViewCell class]]) { return nil; }
self = [arrayOfViews objectAtIndex:0];
}
return self;
}
then you can register this class to be used by the collectionView with
[self.collectionView registerClass:[MyViewCell class] forCellWithReuseIdentifier:#"myCell"];

Answer 2

It's been a while since the question has been asked but I faced the same issue lately.
Eventually, I found the answer here.
In short:
You cannot drag and drop a UICollectionViewCell into a UICollectionView if you are in a .xib file. This is only possible in a storyboard.
The workaround is to create a .xib file for your custom cell and to register the cell manually using:
[self.collectionView registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:CELL_ID];

Answer 3

Define your cell view in a separate nib file. The view must be of type UICollectionViewCell or a subclass.
Then, you must register the nib with your collection view:
- (void)viewDidLoad
{
UINib *cellNib = [UINib nibWithNibName:#"MyNib" bundle:nil];
[self.collectionView registerNib:cellNib forCellWithReuseIdentifier:#"cell"];
}

Answer 4

While these answers are correct, the underlying cause of the problem is quite subtle and Apple needs to update their error message in the log. When you see:
Unknown class MyViewCell in Interface Builder file.
What it actually means is that your source code is missing the #implementation declaration or that the .m file has not been added to the target. So check your code and make sure you have:
#implementation MyViewCell
#end
This is true for both UITableViewCell and UICollectionViewCell.
I discuss the problem further at https://stackoverflow.com/a/12755891/539149 for the general case.
The interesting thing is that if you are missing the #implementation and call:
[self.myCollectionView registerClass:[MyViewCell class] forCellWithReuseIdentifier:#"MyViewCell"];
You will see:
Undefined symbols for architecture armv7:
"_OBJC_CLASS_$_MyViewCell", referenced from:
objc-class-ref in MyViewController.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)
So Apple knows about the problem, they just aren't detecting it during compilation. I would advise against putting custom cells in separate nibs or calling registerClass: forCellWithReuseIdentifier:. It's much cleaner to store the custom cell inside of its container UICollectionView or UITableView in Interface Builder.