UICollectionView does not scroll

I have a UICollectionView set up with a UICollectionViewDataSource that currently provides six items. These are fewer than needed to fill the screen. The problem is that my collection view only scrolls when there are enough items to fill the screen (tested with 10, 20). When displaying fewer items it wont even do this bounce animation I am trying to get, it's just fixed.

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(updateCollectionViewData) name:UIDocumentStateChangedNotification object:nil];

    UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc]init];
    flowLayout.itemSize = CGSizeMake(160, 100);
    flowLayout.minimumInteritemSpacing = 0;
    flowLayout.minimumLineSpacing = 0;

    self.collectionView = [[UICollectionView alloc]initWithFrame:self.view.bounds collectionViewLayout:flowLayout];
    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"Cell"];
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
    self.collectionView.bounces = YES;
    [self.view addSubview:self.collectionView];
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    return [self.collectionViewData count];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
     UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];

    Expense *expense = [self.collectionViewData objectAtIndex:indexPath.row];

    UILabel *label = [[UILabel alloc]initWithFrame:cell.bounds];
    label.text = expense.value;
    label.backgroundColor = [UIColor clearColor];
    label.font = [UIFont fontWithName:@"Miso-Bold" size:30];
    label.textAlignment = NSTextAlignmentCenter;
    [cell addSubview:label];

    cell.backgroundColor = [UIColor colorWithRed:1 - (indexPath.row / 30.0f) green:0 blue:1 alpha:1];

    return cell;
}

Thanks for your help!

bounces, despite it's name, isn't the right property to set. You also need to set alwaysBounceVertical and / or alwaysBounceHorizontal. From the documentation:

If this property is set to YES and bounces is YES, vertical dragging is allowed even if the content is smaller than the bounds of the scroll view. The default value is NO.

Note the confusing name in IB .. https://stackoverflow.com/a/18391029/294884

With storyboards in attributes inspector for collection view "Bounces" and "Bounces Vertically" should be checked.

Setting the height of the UICollectionView to size of UIView will make your scrolling problem disabled. If the UICollectionView is 568 pixels tall then it will only ever need to scroll if it has more than 568 pixels worth of content in it. You should set it to the height of the view it is contained in (same as the width).

Hope it helps you.