UICollectionViewFlowLayout（在 xcode6 下定位 iOS7 时布局不正确）

Question

我需要布置一组照片，如图所示。生成所需布局的代码如下，其中UICollectionViewFlowLayout 是PhotoLayoutReordering 的超类：

@implementation PhotoLayoutReordering

-(instancetype) initWithCoder:(NSCoder *)aDecoder {
self = [super initWithCoder:aDecoder];
if (self) {
    ;// additional set up here
    self.scrollDirection = UICollectionViewScrollDirectionVertical;
}
return self;
}

-(CGSize) calculateSecondaryCellSizeAndMargin {
CGSize cellSize;
cellSize.width = self.collectionView.frame.size.width/NUMBER_OF_COLUMNS;
cellSize.width = cellSize.width - 2*SPACE_BETWEEN_CELLS;
CGSize secondaryCellSize = CGSizeMake(cellSize.width,cellSize.width);
//    NSLog(@"cell width:%1.0f\t cell height:%1.0f\t   margin:%1.0f\n",secondaryCellSize.width,secondaryCellSize.height,_spaceBetweenCells);
//    NSLog(@"number of cells are: %d",(int)[self.collectionView numberOfItemsInSection:0]);
return secondaryCellSize;
}

-(CGSize) calculatePrimaryCellSize {
CGFloat width;
CGSize secondaryCellSize = [self calculateSecondaryCellSizeAndMargin];
width = (NUMBER_OF_COLUMNS-1)* secondaryCellSize.width + NUMBER_OF_COLUMNS*SPACE_BETWEEN_CELLS;
return CGSizeMake(width, width);
}

-(UICollectionViewLayoutAttributes*) layoutAttributesAtIndexPath:(NSIndexPath*) indexPath {
UICollectionViewLayoutAttributes *attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
return attributes;
}

#pragma mark - UICollectionViewLayout overridden methods
-(CGSize) collectionViewContentSize {
CGSize primaryCellSize = [self calculatePrimaryCellSize];
CGFloat heightForPrimaryCell = primaryCellSize.height + NUMBER_OF_COLUMNS*SPACE_BETWEEN_CELLS;
if ([self.collectionView numberOfItemsInSection:0] > NUMBER_OF_COLUMNS) {
    NSUInteger nubmerOfSecondaryRows = [self.collectionView numberOfItemsInSection:0]/NUMBER_OF_COLUMNS;
    CGFloat heightForSecondaryCells = nubmerOfSecondaryRows * [self calculateSecondaryCellSizeAndMargin].height;
    heightForPrimaryCell += heightForSecondaryCells;
}
//    NSLog(@"height of collectionview %1.0f",heightForPrimaryCell);
return CGSizeMake(self.collectionView.frame.size.width, heightForPrimaryCell);
}

-(NSArray*) layoutAttributesForElementsInRect:(CGRect)rect {
NSLog(@"layoutAttributesForElementsInRect");
NSMutableArray *attributesInRect = [NSMutableArray array];
NSInteger numberOfCell = [self.collectionView numberOfItemsInSection:0];
for (int index=0; index < numberOfCell; index++) {
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:index inSection:0];
    [attributesInRect addObject:[self calculateLayouAttributes:indexPath]];
}

for (UICollectionViewLayoutAttributes *attribute in attributesInRect) {
    NSLog(@"%@",attribute);
}
return attributesInRect;
}

-(UICollectionViewLayoutAttributes*) layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
NSLog(@"layoutAttributesForItemAtIndexPath");
return [self calculateLayouAttributes:indexPath];
}

我正在使用 Xcode6。使用 iOS8 运行模拟器时，iPhone4s、iPhone5、iPhone6 和 iPhone6 Plus 的布局是正确的。下图-(NSArray*) layoutAttributesForElementsInRect:返回的属性数组是正确的。

2014-09-16 09:47:30.600 Postlets[3606:212466]    layoutAttributesForElementsInRect 
2014-09-16 09:47:30.600    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1880>    index path: (<NSIndexPath: 0x7afb0dc0> {length = 2, path = 0 - 0});    frame = (2 2; 236 236);  
2014-09-16 09:47:30.600    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1950>    index path: (<NSIndexPath: 0x7afb1900> {length = 2, path = 0 - 1});    frame = (242 2; 76 76);  
2014-09-16 09:47:30.600    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb19d0>    index path: (<NSIndexPath: 0x7afb1910> {length = 2, path = 0 - 2});    frame = (242 82; 76 76);  
2014-09-16 09:47:30.600    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1a60>    index path: (<NSIndexPath: 0x7afb1a50> {length = 2, path = 0 - 3});    frame = (242 162; 76 76);  
2014-09-16 09:47:30.600    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1af0>    index path: (<NSIndexPath: 0x7afb1ae0> {length = 2, path = 0 - 4});    frame = (2 242; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1b90>    index path: (<NSIndexPath: 0x7afb0be0> {length = 2, path = 0 - 5});    frame = (82 242; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1c20>    index path: (<NSIndexPath: 0x7afb1c10> {length = 2, path = 0 - 6});    frame = (162 242; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1ca0>    index path: (<NSIndexPath: 0x7afb1920> {length = 2, path = 0 - 7});    frame = (242 242; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1d20>    index path: (<NSIndexPath: 0x7afb1930> {length = 2, path = 0 - 8});    frame = (2 322; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1de0>    index path: (<NSIndexPath: 0x7afb1940> {length = 2, path = 0 - 9});    frame = (82 322; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1e70>    index path: (<NSIndexPath: 0x7afb1e60> {length = 2, path = 0 - 10});    frame = (162 322; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1f00>    index path: (<NSIndexPath: 0x7afb1ef0> {length = 2, path = 0 - 11});    frame = (242 322; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb1f90>    index path: (<NSIndexPath: 0x7afb1f80> {length = 2, path = 0 - 12});    frame = (2 402; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb2020>    index path: (<NSIndexPath: 0x7afb2010> {length = 2, path = 0 - 13});    frame = (82 402; 76 76);  
2014-09-16 09:47:30.601    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb20b0>    index path: (<NSIndexPath: 0x7afb20a0> {length = 2, path = 0 - 14});    frame = (162 402; 76 76);  
2014-09-16 09:47:30.602    Postlets[3606:212466] <UICollectionViewLayoutAttributes: 0x7afb2140>    index path: (<NSIndexPath: 0x7afb2130> {length = 2, path = 0 - 15});    frame = (242 402; 76 76);

但是，在 iOS7.1 上运行时，第一个单元格的布局对于 iPhone4s/iPhone5 是不正确的。

我不确定我是否忽略了某些内容，或者 UICollectionViewFlowLayout 是否存在错误？感谢您的意见。

更新：UICollectionViewCell 的子类有一个UIImageView。在情节提要中，我使用自动布局来限制 UIImageView 的大小，使其在所有 4 个面上刷新到 UICollectionViewCell 的子类。针对 iOS7 的 Xcode6 中对约束的解释在某种程度上被误解了（至少这是我的猜测。）我决定使用 Visual Format Language 添加约束，如下所示：

-(void) layoutViews {
_imageView = [[RemoteImageView alloc] init]; // this is a subclass of UIImageView
_imageView.translatesAutoresizingMaskIntoConstraints = NO;
_imageView.contentMode = UIViewContentModeScaleAspectFill;
_imageView.clipsToBounds = YES;

[self addSubview:_imageView];
NSDictionary *views = NSDictionaryOfVariableBindings(_imageView);//,spinner);
[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|[_imageView]|" options:0 metrics:nil views:views]];
[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[_imageView]|" options:0 metrics:nil views:views]];
}

UIImageView 现在大小合适，可以在 iOS7/8 的所有 4 个面上与UICollectionViewCell 齐平。希望这对那里的一些开发人员有用... 向 Apple 提交错误报告 (#18415152)。
2014 年 10 月 7 日更新：由 Apple 关闭（与错误 #18312246 重复）

Answer 1

你在哪里设置单元格的大小？看起来您缺少 collectionView:layout:sizeForItemAtIndexPath: 委托方法。您可以在此处设置单个单元格的大小。