UICollectionView must be initialized with a non-nil layout parameter

Question

I'm new to UICollectionView and I'm following a tutorial I found on the web but I'm stuck on an error I can't figure out. Here's a bit of context.

In the debugger I can see that following is happening:

• numberOfSectionsInCollectionView: is called and I return 1
• collectionView:numberOfItemsInSection: is called and I return the size of the model (20)
• collectionView:layout:sizeForItemAtIndexPath: gets called once for each item in the model
• collectionView:layout:insetForSectionAtIndex: is called

• collectionView:cellForItemAtIndexPath: gets called and it crashes on this line...

  UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"MyCell" forIndexPath:indexPath];
  

with this error...

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'UICollectionView must be initialized with a non-nil layout parameter'

When I pause execution on that line and check the console it appears that there is a layout...

(lldb) po collectionView.collectionViewLayout
(UICollectionViewLayout *) $4 = 0x07180fd0 <UICollectionViewFlowLayout: 0x7180fd0>

The UICollectionView is part of the one and only scene in the storyboard. In viewController.m there are no other UICollectionViews created by any means.

Does anyone have any ideas?

Answer 1

This worked for me :

UICollectionViewFlowLayout *aFlowLayout = [[UICollectionViewFlowLayout alloc] init];     [aFlowLayout setItemSize:CGSizeMake(200, 140)];     [aFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal]; myCollectionViewController = [[MyCollectionViewController alloc]initWithCollectionViewLayout:flowLayout]; 

If you are creating UICollectionView programmatically a layout is required.

Answer 2

As it turns out the problem was with registerClass:. I had this:

[self.collectionView registerClass:[UICollectionView class] 
        forCellWithReuseIdentifier:@"MyCell"];

but it should have been this:

[self.collectionView registerClass:[UICollectionViewCell class] 
        forCellWithReuseIdentifier:@"MyCell"];

So the dequeue method was creating a UICollectionView instead of a UICollectionViewCell.