UICollectionView不滚动

我有一个UICollectionView设置UICollectionViewDataSource，目前提供六个项目。这些比填写屏幕所需要的要少。问题是我的收藏视图只在有足够的项目填满屏幕时滚动（用10,20测试）。当显示更少的项目，它甚至不会做这个反弹动画，我试图得到它只是固定的。UICollectionView不滚动

- (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; 
}

感谢您的帮助！

来源

2013-04-17 Dario