Question

目前我有一个水平滚动的标准UICollectionViewFlowLayout，但如果高度允许，它会将项目相互堆叠。
相反，我希望有一个水平滚动的集合视图，不会断行，即不会将项目相互堆叠 - 只需一个线性流。
这个问题甚至比this question更简单，因为不需要垂直滚动。因此那里的答案不适用。

我想我可以继承UICollectionViewFlowLayout，但我不确定哪些方法必须被覆盖我检查了在显示项目之前调用了当前-layoutAttributesForElementsInRect:（但不是-layoutAttributesForItemAtIndexPath:） NSArray返回的-layoutAttributesForElementsInRect:包含每个项目的框架（其中一些是相互堆叠的）。
我可以在-collectionView:layout:sizeForItemAtIndexPath:中抑制这种堆叠，如果我在这个方法中增加所有项目的高度大于最大高度的一半，但是项目本身是垂直缩放的，这是我不想要的。

所以我的问题是：什么以及如何覆盖UICollectionViewFlowLayout或UICollectionViewLayout的方法来获得这种线性流？

Answer 1

我自己解决了这个问题，但也许这有助于其他人我部分使用了Bryan Hansen的UICollectionView custom layout tutorial：

我将UICollectionViewFlowLayout子类化，添加了属性，并且只实现了3种方法（下面的伪代码）：

@interface LinearCollectionViewFlowLayout : UICollectionViewFlowLayout
@end  

@interface LinearCollectionViewFlowLayout ()
@property (nonatomic, strong) NSArray *layoutInfo;    // layout infos for the collection view elements
@property                     CFFloat *maxItemHeight; // max height of items in the collection view
@end

@implementation LinearCollectionViewFlowLayout

- (void)prepareLayout
{
    // Get from the collection views datasource an array of all items in the collection view
    ......

    // Loop through all items and store max height in the property.
    ......

    CGFloat xOffsetOfNextItem = 0;
    NSMutableArray *tmpLayoutInfo = [NSMutableArray array];
    // Loop through all items to compute x and y origin of every item in the collection view
    for (int index = 0; index < nrCollectionViewItems; index++) {
        // Get the next item via its index and store it in a variable nextItem
        ......
        CGSize  nextItemSize   = nextItem.size;       // Get the size of the next item
        CGFloat nextItemHeight = nextItemSize.height; // Get the height of the next item

        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:index inSection:0]; // Assuming that there is only 1 section in the collection view
        UICollectionViewLayoutAttributes *itemAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
        CGFloat yOffset = self.maxItemHeight/2.0 - nextImageHeight/2.0 + 5; // center the item vertically (add spacer)
        CGRect itemFrame = CGRectMake(xOffsetOfNextItem, yOffset, nextItemSize.width, nextItemHeight);
        itemAttributes.frame = itemFrame; // store the frame of the item
        tmpLayoutInfo[index] = itemAttributes;

        xOffsetOfNextIcon += nextItemSize.width + 5; // Compute x of next item (add a spacer)
    }
    self.collectionView.contentWidth = xOffsetOfNextItem; // Store the width of the collection view

    self.layoutInfo = [NSArray arrayWithArray:tmpLayoutInfo]; // Store all layout infos
}

//-----------------------------------------------------------------------------------------------------------------

- (CGSize)collectionViewContentSize
{
    CGSize size = [super collectionViewContentSize]; // Get the collection view size as computed by UICollectionViewFlowLayout
    size.width = self.collectionView.contentWidth;   // Replace the width by the value computed in prepareLayout
    return size;
}

//-----------------------------------------------------------------------------------------------------------------

-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect
{
    // Set up an array of layout attributes only for the items in rect
    NSMutableArray *attributesForElementsInRect = [NSMutableArray array];
    for (UICollectionViewLayoutAttributes *nextAttributes in self.layoutInfo) {
        CGRect nextFrame = nextAttributes.frame;
        if (CGRectIntersectsRect(rect, nextFrame)) {
            [attributesForElementsInRect addObject:nextAttributes];
        }
    }

    return [NSArray arrayWithArray:attributesForElementsInRect];
}

@end

如何设置没有换行符的水平UICollectionViewFlowLayout

1 个答案: