我可以有一个UICollectionViewFlowLayout与scrollDirection不同的布局方向

Question

UICollectionViewFlowLayout很好，但是，我希望它稍微调整一下，以便scrollDirection与布局方向不同。我想要的例子是跳板主屏幕或表情符号键盘，你可以向左/向右滑动，但单元格是从左到右，从上到下(而不是从上到下，从左到右，因为它们是与UICollectionViewFlowLayout与scrollDirection设置为水平)。有人知道我如何可以轻松子类FlowLayout使这种变化?我很失望，他们没有一个layoutDirection除了scrollDirection在UICollectionViewFlowLayout对象:(

@rdelmar我实现了一些类似于你的解决方案，这是有效的(不像我想的那么优雅)，但我注意到，偶尔项目从集合中消失，除非重新绘制，这就是为什么我不接受答案。下面是我最后写的:

@interface UICollectionViewPagedFlowLayout : UICollectionViewFlowLayout
@property int width;
@property int height;
@end
@implementation UICollectionViewPagedFlowLayout
#warning MINOR BUG: sometimes symbols disappear
- (CGSize)collectionViewContentSize {
    CGSize size = [super collectionViewContentSize];
    // make sure it's wide enough to cover all the objects
    size.width = self.collectionView.bounds.size.width * [self.collectionView numberOfSections];
    return size;
}
- (NSArray*) layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray *array = [super layoutAttributesForElementsInRect:rect];
    CGRect visibleRect;
    visibleRect.origin = self.collectionView.contentOffset;
    visibleRect.size = self.collectionView.bounds.size;
    for (UICollectionViewLayoutAttributes* attributes in array) {
        if (CGRectIntersectsRect(attributes.frame, rect)) {
            // see which section this is in
            CGRect configurableRect = UIEdgeInsetsInsetRect(visibleRect, self.sectionInset);
            int horizontalIndex = attributes.indexPath.row % self.width;
            int verticalIndex = attributes.indexPath.row / self.width;
            double xspace = (configurableRect.size.width - self.width * self.itemSize.width) / self.width;
            double yspace = (configurableRect.size.height - self.height * self.itemSize.height) / self.height;
            attributes.center = CGPointMake(attributes.indexPath.section * visibleRect.size.width + self.sectionInset.left + (self.itemSize.width + xspace) * horizontalIndex + self.itemSize.width / 2, self.sectionInset.top + (self.itemSize.height + yspace) * verticalIndex + self.itemSize.height / 2);
        }
    }
    return array;
}
@end

Answer 1

IIRC，这正是在WWDC 2012会议上UICollectionView的演示。

Answer 2

我不知道是否容易，我想这取决于你的定义。我做了一个项目，我的布局接近你想要的。这将水平地排列行，从左到右，从上到下。我的数据源是一个数组的数组，其中每个子数组提供一行的数据。

#import "SimpleHorizontalLayout.h" // subclass of UICollectionViewFlowLayout
#define kItemSize 60
@implementation SimpleHorizontalLayout 

-(CGSize)collectionViewContentSize {
    NSInteger xSize = [self.collectionView numberOfItemsInSection:0] * (kItemSize + 20); // the 20 is for spacing between cells.
    NSInteger ySize = [self.collectionView numberOfSections] * (kItemSize + 20);
    return CGSizeMake(xSize, ySize);
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)path {
    UICollectionViewLayoutAttributes* attributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:path];
    attributes.size = CGSizeMake(kItemSize,kItemSize);
    NSInteger xValue = kItemSize/2 + path.row * (kItemSize +20) ;
    NSInteger yValue = kItemSize + path.section * (kItemSize +20);
    attributes.center = CGPointMake(xValue, yValue);
    return attributes;
}

-(NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {
    NSInteger minRow =  (rect.origin.x > 0)?  rect.origin.x/(kItemSize +20) : 0; // need to check because bounce gives negative values for x.
    NSInteger maxRow = rect.size.width/(kItemSize +20) + minRow;
    NSMutableArray* attributes = [NSMutableArray array];
    for(NSInteger i=0 ; i < self.collectionView.numberOfSections; i++) {
        for (NSInteger j=minRow ; j < maxRow; j++) {
            NSIndexPath* indexPath = [NSIndexPath indexPathForItem:j inSection:i];
            [attributes addObject:[self layoutAttributesForItemAtIndexPath:indexPath]];
        }
    }
    return attributes;
}

Answer 3

直到Apple添加了一个简单的标志来改变流布局的布局方向，我才结束了子类化。有些东西是特定于我的实现，但它可能会帮助其他人:

@interface UICollectionViewPagedFlowLayout : UICollectionViewFlowLayout
@property int width;
@property int height;
@end
@implementation UICollectionViewPagedFlowLayout
#warning MINOR BUG: sometimes items disappear
- (CGSize)collectionViewContentSize {
    CGSize size = [super collectionViewContentSize];
    size.width = self.collectionView.bounds.size.width * [self.collectionView numberOfSections];
    return size;
}
- (NSArray*) layoutAttributesForElementsInRect:(CGRect)rect {
    NSArray *array = [super layoutAttributesForElementsInRect:rect];
    CGRect visibleRect;
    visibleRect.origin = self.collectionView.contentOffset;
    visibleRect.size = self.collectionView.bounds.size;
    for (UICollectionViewLayoutAttributes* attributes in array) {
        if (CGRectIntersectsRect(attributes.frame, rect)) {
            // see which section this is in
            CGRect configurableRect = UIEdgeInsetsInsetRect(visibleRect, self.sectionInset);
            int horizontalIndex = attributes.indexPath.row % self.width;
            int verticalIndex = attributes.indexPath.row / self.width;
            double xspace = (configurableRect.size.width - self.width * self.itemSize.width) / self.width;
            double yspace = (configurableRect.size.height - self.height * self.itemSize.height) / self.height;
            attributes.center = CGPointMake(attributes.indexPath.section * visibleRect.size.width + self.sectionInset.left + (self.itemSize.width + xspace) * horizontalIndex + self.itemSize.width / 2, self.sectionInset.top + (self.itemSize.height + yspace) * verticalIndex + self.itemSize.height / 2);
        }
    }
    return array;
}
@end