cellForItemAtIndexPath not called but numberOfItem

问题:

This could be a duplicate post but I haven't found the solution in any of this:

I'm setting my UICollectionView as:

UINib *nib = [UINib nibWithNibName:@"CollectionViewCell"
                           bundle:[NSBundle mainBundle]];
[_collectionView registerNib: nib forCellWithReuseIdentifier:@"bCell"];

(I've tried to set delegate, without delegate, etcetera).

But then, only the

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section gets called while

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath doesn't.

I've checked the numberOfItemsInSection I return, and it's always > 0 (it's exactly 17).

I've checked to call [_collectionView reloadData]; and nothing happens either.

I've tried different things but I can't make it work.

Furthermore, my UICollectionView should be here but it's not:

Does anyone have a clue? Thank you.

回答1:

Ok I think this could be useful for future problems with this...

It was because of constraints on the StoryBoard. I don't really understand why that happens, because I just had fixed an horizontal space. I removed the horizontal space as constraint for that View and everything works fine.

Well, let's life flow.

回答2:

I also face same issue and finally got to know that i have passed wrong class object for collectionViewLayout , i change to UICollectionViewFlowLayout instead of UICollectionViewLayout while creating object for UICollectionView like below its stared calling all delegate method.

 collectionView = UICollectionView(frame: CGRectMake(5, 0, 400, 40) , collectionViewLayout: UICollectionViewFlowLayout())

回答3:

Add this to viewDidLoad:

self.automaticallyAdjustsScrollViewInsets = NO;

回答4:

1. cellForItemAtIndexPath will be called when you return More than 0 Items on numberOfItemsInSection method.

2. Check that your UICollectionViewFlowLayout is correct or your own. UICollectionViewLayout is abstract class you can't use it directly

3. Check the size of the collection view cell & Collection view.

4. Try to set your collectionview size by in code. [yourCollectionViewFlowLayout setItemSize:CGSizeMake(200, 200)];

5.If any of them NOT works, then kill the XCode & restart . Sometimes it will fix the issue.

Apple says

The UICollectionViewLayout class is an abstract base class that you subclass and use to generate layout information for a collection view. The job of a layout object is to determine the placement of cells, supplementary views, and decoration views inside the collection view’s bounds and to report that information to the collection view when asked. The collection view then applies the provided layout information to the corresponding views so that they can be presented onscreen.

You must subclass UICollectionViewLayout in order to use it. Before you consider subclassing, though, you should look at the UICollectionViewFlowLayout class to see if it can be adapted to your layout needs.

回答5:

I meet this problem too. I checked all the possible issues, everything looks ok. Then I tried to changed the reload methods.

[self.colView reloadData] -> [self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:x]];

Then all things worked. However I still don't understand how.

回答6:

I just found that NONE of cellForItemAtIndexPath gets called (in iOS 10) as long as at least ONE cell has a height of zero.

Disclaimer: sorry if this should have been a comment - not enough reputation.

回答7:

For me the cellForItemAtIndexPath not called for the first time after i set the constraint of the collectionView to 0 and then again setting it to its Actual Size.

 @IBOutlet weak var collectionVwHeightContraint: NSLayoutConstraint!
 if attachments.count > 0 {

     collectionVwHeightContraint.constant = 100
 }else {

     collectionVwHeightContraint.constant = 0
 }
 // collectionVwHeightContraint is my collectionView height Contraint outlet

I solved this by calling:

self.view.layoutIfNeeded()

Hope it will help someone :)

回答8:

What helped me was to set the correct itemSize. My cellForItemAtIndexPath was not being called because of the wrong height.

So I set the size at:

[self.myCollectionViewFlowLayout setItemSize:CGSizeMake(170, 300)];

回答9:

For me the issue was that I was creating my Collection View programmatically but I had given it CGRectZero as its frame. I was laying it out using Auto Layout after viewDidLoad. If I lay out the collection view while the view controller is loading, it ends up calling cellForItemAtIndexPath: correctly.

回答10:

I had same problem with collection view outlet on a storyboard with "standard" constraints (bottom, top, leading, trailing fixed to inner view).

I solved in this way:

let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()
layout.itemSize = self.collectionView.frame.size

回答11:

For me it was that my collectionView's container didn't have translatesAutoresizingMaskIntoConstraints = false

回答12:

I had faced a similar problem. The issue was with the numberOfItems in section. Your cellForRowAtIndexPath might not be called if either your number of sections or number of rows in section is below zero.