UICollectionView自定义行分隔符

我从三个想法开始如何制作它：

I started with three ideas how to make it:

• 在单元格中实现这些分隔符


• 使用纯黑色背景和 minimumLineSpacing ，因此我们会在单元格之间的空格中看到背景


• 使用自定义布局并将此分隔符实现为装饰

• implement these separators right inside the cells
• use solid black background with minimumLineSpacing, thus we will see background in spaces between cells
• use custom layout and implement this separators as decorations

前两个变体被拒绝是因为意识形态不一致，自定义动画以及收集下面的内容。此外，我已经有了自定义布局。

First two variants were rejected because ideologic inconsistency, custom animations and having content below collection. Also I already have a custom layout.

我将描述使用 UICollectionViewFlowLayout 的自定义子类的步骤。

I will describe the steps with a custom subclass of UICollectionViewFlowLayout.

实施自定义 UICollectionReusableView 子类。

@interface FLCollectionSeparator : UICollectionReusableView

@end

@implementation FLCollectionSeparator

- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor blackColor];
    }

    return self;
}

- (void)applyLayoutAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes {
    self.frame = layoutAttributes.frame;
}

@end

- 2 -

说布局使用自定义装饰。还要在单元格之间建立行间距。

--2--

Say layout to use custom decorations. Also make line spacing between cells.

UICollectionViewFlowLayout* layout = (UICollectionViewFlowLayout*) self.newsCollection.collectionViewLayout;
[layout registerClass:[FLCollectionSeparator class] forDecorationViewOfKind:@"Separator"];
layout.minimumLineSpacing = 2;

- 3 -

In自定义 UICollectionViewFlowLayout 子类我们应该从 layoutAttributesForElementsInRect 返回装饰 UICollectionViewLayoutAttributes 。

--3--

In custom UICollectionViewFlowLayout subclass we should return UICollectionViewLayoutAttributes for decorations from layoutAttributesForElementsInRect.

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
    ... collect here layout attributes for cells ... 

    NSMutableArray *decorationAttributes = [NSMutableArray array];
    NSArray *visibleIndexPaths = [self indexPathsOfSeparatorsInRect:rect]; // will implement below

    for (NSIndexPath *indexPath in visibleIndexPaths) {
        UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForDecorationViewOfKind:@"Separator" atIndexPath:indexPath];
        [decorationAttributes addObject:attributes];
    }

    return [layoutAttributesArray arrayByAddingObjectsFromArray:decorationAttributes];
}

- 4 -

对于可见的rect，我们应该返回可见的装饰索引pathes。

--4--

For visible rect we should return visible decorations index pathes.

- (NSArray*)indexPathsOfSeparatorsInRect:(CGRect)rect {
    NSInteger firstCellIndexToShow = floorf(rect.origin.y / self.itemSize.height);
    NSInteger lastCellIndexToShow = floorf((rect.origin.y + CGRectGetHeight(rect)) / self.itemSize.height);
    NSInteger countOfItems = [self.collectionView.dataSource collectionView:self.collectionView numberOfItemsInSection:0];

    NSMutableArray* indexPaths = [NSMutableArray new];
    for (int i = MAX(firstCellIndexToShow, 0); i <= lastCellIndexToShow; i++) {
        if (i < countOfItems) {
            [indexPaths addObject:[NSIndexPath indexPathForRow:i inSection:0]];
        }
    }
    return indexPaths;
}

- 5 -

我们还应该实现 layoutAttributesForDecorationViewOfKind 。

- (UICollectionViewLayoutAttributes *)layoutAttributesForDecorationViewOfKind:(NSString *)decorationViewKind atIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewLayoutAttributes *layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForDecorationViewOfKind:decorationViewKind withIndexPath:indexPath];
    CGFloat decorationOffset = (indexPath.row + 1) * self.itemSize.height + indexPath.row * self.minimumLineSpacing;
    layoutAttributes.frame = CGRectMake(0.0, decorationOffset, self.collectionViewContentSize.width, self.minimumLineSpacing);
    layoutAttributes.zIndex = 1000;

    return layoutAttributes;
}

- 6 -

有时我发现这个解决方案给出了装饰外观的视觉故障，通过实现 initialLayoutAttributesForAppearingDecorationElementOfKind 来修复。

- (UICollectionViewLayoutAttributes *)initialLayoutAttributesForAppearingDecorationElementOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)decorationIndexPath {
    UICollectionViewLayoutAttributes *layoutAttributes =  [self layoutAttributesForDecorationViewOfKind:elementKind atIndexPath:decorationIndexPath];
    return layoutAttributes;
}

这就是全部。没有太多的代码，但做得很好。

That's all. Not too much code but done right.