UICollectionView not recognized in collectionView numberOfItemsInSection:

Question

I have a problem I can't solve for some hours now...

I have multiple UICollectionViews with different numbers of cells and different cellsizes. The CollectionViews are created programmatically and the delegates and datasources are set.

The collectionviews are created like this:

UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
[layout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
collectionViewOne = [[UICollectionView alloc] initWithFrame:CGRectMake(0,0,320,150) collectionViewLayout:layout];
[collectionViewOne setTag:99];
[collectionViewOne setDataSource:self];
[collectionViewOne setDelegate:self];
[collectionViewOne registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cell"];
[collectionViewOne setBackgroundColor:bgColor];
[collectionViewOne setShowsHorizontalScrollIndicator:NO];
[collectionViewOne setBounces:YES];
[collectionViewOne setAlwaysBounceHorizontal:YES];
[collectionViewOne setScrollEnabled:YES];
[collectionViewOne setRestorationIdentifier:@"collectionViewOne"];
[scrollView addSubview:collectionViewOne];

My functions are like these:

- (NSInteger)collectionView:(UICollectionView*)collectionView numberOfItemsInSection:(NSInteger)section {

    NSLog(@"restorationIdentifier: %@", collectionView.restorationIdentifier);

    if (collectionView == collectionViewOne)
    {
        return 3;
    }
    else if (collectionView == collectionViewTwo)
    {
        return 4;
    }
    else
    {
        return 1;
    }
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    NSLog(@"restorationIdentifier: %@", collectionView.restorationIdentifier);

    if (collectionView == collectionViewOne)
    {
        return CGSizeMake(100, 150);
    }
    else if (collectionView == collectionViewTwo)
    {
        return CGSizeMake(200, 150);
    }
    else
    {
        return CGSizeMake(200, 150);
    }
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    NSLog(@"restorationIdentifier: %@", collectionView.restorationIdentifier);

    if (collectionView == collectionViewOne)
    {
        UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
        imageView.image = [UIImage imageNamed:@"image.png"]; 
        [cell addSubview:imageView];
    }
    else if (collectionView == collectionViewTwo)
    {
        //create cell of type 2
    }
    return cell;
}

In my log I get the following output (for example):

restorationIdentifier in numberOfItemsInSection: (null) restorationIdentifier in sizeForItemAtIndexPath : (null) restorationIdentifier cellForItemAtIndexPath: collectionViewOne

collectionViewOne is the restorationIdentifier on collectionViewOne. So why is it not recognized in the first two methods?

Ofcourse the result is that I get crashes because the cellsizes and number of cells in the different CollectionViews are not properly set. The error:

*** Assertion failure in -[UICollectionViewData validateLayoutInRect:], /SourceCache/UIKit_Sim/UIKit-2903.2/UICollectionViewData.m:341
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UICollectionView recieved layout attributes for a cell with an index path that does not exist: <NSIndexPath: 0x8c31c10> {length = 2, path = 0 - 2}'

How can I fix this?

Answer 1

This is solved. The problem was the fact that I used the same UICollectionViewFlowLayout for both UICollectionViews. This caused the exception.

In the end I used different classes for the two controllers, this solved the problem of selecting the right CollectionView in the delegate's methods.

Thanks all for your input!

Answer 2

You could use the tag property of the collection view to identify which collection view is which. Like this:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    NSLog(@"restorationIdentifier: %@", collectionView.restorationIdentifier);

    if (collectionView.tag == collectionViewOneTag)
    {
        //create cell of type 1
    }
    else if (collectionView.tag == collectionViewTwoTag)
    {
        //create cell of type 2
    }

    return cell;
}

Where collectionViewOneTag and collectionViewTwoTag are integers that can be defined in code or in the xib file.

Hope that helps.