自动布局在UICollectionViewCell不工作

我有一个包含了一个的UITextView细胞的简单UICollectionView。所述的UITextView约束到小区的边缘，因此，它们应保持的大小与细胞大小相同。

I have a simple UICollectionView with cells that have a single UITextView. The UITextView is constrained to the edges of the cell, so they should stay the same size as the cell size.

我遇到的问题是，由于某种原因，当我通过的CollectionView指定单元格的大小这些限制不工作：布局：sizeForItemAtIndexPath：

The problem I'm having is that for some reason these constraints are not working when I specify the cell size via collectionView:layout:sizeForItemAtIndexPath:.

我在故事板设置为320x50的单元格大小。如果我返回一个大小与sizeForItemAtIndexPath单元尺寸的2倍的高度：，所述的UITextView停留尽管我设置约束相同的高度。我使用X code 6 GM。

I have the cell size set to 320x50 in the Storyboard. If I return a size with 2 times the height of the cell size with sizeForItemAtIndexPath:, the UITextView stays the same height despite the constraints I set. I am using Xcode 6 GM.

我的视图控制器code是：

My view controller code is:

@implementation TestViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
}

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

    UICollectionViewCell *c = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];

    NSLog(@"%f", c.frame.size.height);

    UITextView *tv = (UITextView *)[c viewWithTag:9];
    NSLog(@"%f", tv.frame.size.height);

}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return 1;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];

    return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewFlowLayout *flowLayout = (UICollectionViewFlowLayout *)collectionView.collectionViewLayout;

    CGSize size = flowLayout.itemSize;

    size.height = size.height * 2;

    return size;
}

@end

在viewDidAppear这些日志：给我的输出：
结果
100.00000
结果
50.00000
结果
正如你所看到的，UITextView的高度不与细胞改变高度。

Those logs in viewDidAppear: give me an output of:
100.00000
50.00000
As you can see, the UITextView height doesn't change with the cell height.

结果
这是我设置了在UICollectionViewCell限制的UITextView中的故事板的截图：

Here's a screenshot of the storyboard I set up with a UITextView constrained in the UICollectionViewCell:

我知道使用自动布局约束的正常工作与UITableViewCells和动态调整。我不知道为什么它不是在这种情况下工作。没有人有任何想法？

I know using auto layout constraints works fine with UITableViewCells and dynamic resizing. I have no idea why it's not working in this case. Does anyone have any ideas?