背景
近期公司启动了Pad项目，项目中大部分的功能实现都是基于CollectionView实现的，并且cell的高是动态变化的，因此花了一些时间对瀑布流的实现做了些研究。以下就是其实现过程
原理
看了下 UICollectionViewLayout 布局的方法列表，发现最终还是对其中的四个分类方法进行重写
// 1.CollectionView的所有布局
- (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect;
// 2.每个Item的布局
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath;
// 3.每个Section的头和尾布局
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath;
// 4.整个CollectionView的ContentSize
- (CGSize)collectionViewContentSize;
实现步骤
1、系统方法实现
#pragma mark 系统方法
- (instancetype)init {
if (self = [super init]) {
self.scrollDirection = UICollectionViewScrollDirectionVertical;
// 布局的数组
self.layoutAttributeArray = @[].mutableCopy;
}
return self;
}
- (void)prepareLayout {
[super prepareLayout];
[self.layoutAttributeArray removeAllObjects];
// 初始化列高集合(记录纵向滑动的最下侧位置)
NSMutableArray *columnHeightArray = @[].mutableCopy;
for (NSInteger i = 0; i < self.columnCount; i ++) {
[columnHeightArray addObject:@(self.edgeInset.top)];
}
self.columnHeightArray = columnHeightArray;
// 初始化行宽集合(记录横向滑动的最右侧位置)
NSMutableArray *rowWidthArray = @[].mutableCopy;
for (NSInteger i = 0; i < self.rowCount; i ++) {
[rowWidthArray addObject:@(self.edgeInset.left)];
}
self.rowWidthArray = rowWidthArray;
NSInteger sectionCount = [self.collectionView numberOfSections];
for (NSInteger section = 0; section < sectionCount; section++) {
// 添加Header
if ([self.delegate respondsToSelector:@selector(flowLayout:sizeForHeaderInSection:)]) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:section];
UICollectionViewLayoutAttributes *attribute = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
if (attribute) {
[self.layoutAttributeArray addObject:attribute];
}
}
NSInteger rowCount = [self.collectionView numberOfItemsInSection:section];
// 获取每条 Cell
for (NSInteger row = 0; row < rowCount; row++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:row inSection:section];
UICollectionViewLayoutAttributes *attribute = [self layoutAttributesForItemAtIndexPath:indexPath];
[self.layoutAttributeArray addObject:attribute];
}
// 添加Footer
if ([self.delegate respondsToSelector:@selector(flowLayout:sizeForFooterInSection:)]) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:0 inSection:section];
UICollectionViewLayoutAttributes *attribute = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter atIndexPath:indexPath];
if (attribute) {
[self.layoutAttributeArray addObject:attribute];
}
}
}
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes *attribute = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
attribute.frame = [self itemFrameWithIndexPath:indexPath];
return attribute;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath {
CGRect frame = CGRectZero;
if ([elementKind isEqualToString:UICollectionElementKindSectionHeader]) {
frame = [self headerFrameWithIndexPath:indexPath];
} else if ([elementKind isEqualToString:UICollectionElementKindSectionFooter]) {
frame = [self footerFrameWithIndexPath:indexPath];
}
// 纵向滑动时 高度小于0.1 不显示
if (self.scrollDirection == UICollectionViewScrollDirectionVertical && frame.size.height <= 0.1) {
return nil;
}
// 横向滑动时 宽度小于0.1 不显示
if (self.scrollDirection == UICollectionViewScrollDirectionHorizontal && frame.size.width <= 0.1) {
return nil;
}
UICollectionViewLayoutAttributes *attribute = [UICollectionViewLayoutAttributes layoutAttributesForSupplementaryViewOfKind:elementKind withIndexPath:indexPath];
attribute.frame = frame;
return attribute;
}
- (nullable NSArray<__kindof UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {
return self.layoutAttributeArray;
}
- (CGSize)collectionViewContentSize {
// 竖向滑动
if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
CGFloat maxHeight = 0;
for (NSNumber *column in self.columnHeightArray) {
CGFloat columnHeight = [column doubleValue];
maxHeight = MAX(columnHeight, maxHeight);
}
return CGSizeMake(0, maxHeight - self.edgeInset.top);
}
// 横向滑动
else if (self.scrollDirection == UICollectionViewScrollDirectionHorizontal) {
CGFloat maxWidth = 0;
for (NSNumber *row in self.rowWidthArray) {
CGFloat rowWidth = [row doubleValue];
maxWidth = MAX(rowWidth, maxWidth);
}
return CGSizeMake(maxWidth - self.edgeInset.left, 0);
}
return CGSizeZero;
}
2、布局方法实现
#pragma mark Helper
- (CGRect)itemFrameWithIndexPath:(NSIndexPath *)indexPath {
CGFloat collectionW = self.collectionView.frame.size.width;
CGFloat collectionH = self.collectionView.frame.size.height;
CGSize itemSize = [self.delegate flowLayout:self sizeForItemAtIndexPath:indexPath];
CGFloat itemW = itemSize.width;
CGFloat itemH = itemSize.height;
// 内边距
UIEdgeInsets edgeInset = self.edgeInset;
//
CGFloat itemX = edgeInset.left;
CGFloat itemY = edgeInset.top;
CGRect frame = CGRectZero;
// 竖向滑动
if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
itemW = (collectionW-edgeInset.left-edgeInset.right-(self.columnCount-1)*self.columnMargin)/self.columnCount;
// 获取最低列的位置
CGFloat minColumnHeight = [self.columnHeightArray.firstObject doubleValue];
NSInteger minColumn = 0;
for (NSInteger i = 0; i < self.columnHeightArray.count; i++) {
CGFloat columnHeight = [self.columnHeightArray[i] doubleValue];
if (minColumnHeight > columnHeight) {
minColumnHeight = columnHeight;
minColumn = i;
}
}
// 设置item位置
itemX = edgeInset.left + minColumn * (itemW + self.columnMargin);
itemY = minColumnHeight;
frame = CGRectMake(itemX, itemY, itemW, itemH);
// 更新最低高度的
self.columnHeightArray[minColumn] = @(CGRectGetMaxY(frame) + self.rowMargin);
}
// 横向滑动
else {
itemH = (collectionH-edgeInset.top-edgeInset.bottom-(self.rowCount-1)*self.rowMargin)/self.rowCount;
// 获取最低列的位置
CGFloat minRowWidth = [self.rowWidthArray.firstObject doubleValue];
NSInteger minRow = 0;
for (NSInteger i = 0; i < self.rowWidthArray.count; i++) {
CGFloat rowWidth = [self.rowWidthArray[i] doubleValue];
if (minRowWidth > rowWidth) {
minRowWidth = rowWidth;
minRow = i;
}
}
// 设置item位置
itemX = minRowWidth;
itemY = edgeInset.top + minRow * (itemH + self.rowMargin);
frame = CGRectMake(itemX, itemY, itemW, itemH);
// 更新最低宽度的位置
self.rowWidthArray[minRow] = @(CGRectGetMaxX(frame) + self.columnMargin);
}
return frame;
}
- (CGRect)headerFrameWithIndexPath:(NSIndexPath *)indexPath {
CGSize headerSize = CGSizeZero;
if ([self.delegate respondsToSelector:@selector(flowLayout:sizeForHeaderInSection:)]) {
headerSize = [self.delegate flowLayout:self sizeForHeaderInSection:indexPath.section];
}
CGFloat headX = 0;
CGFloat headY = 0;
CGFloat headW = headerSize.width;
CGFloat headH = headerSize.height;
CGRect headFrame = CGRectZero;
// 竖向滑动
if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
headW = CGRectGetWidth(self.collectionView.frame);
if (indexPath.section == 0) {
headY = self.edgeInset.top;
} else {
for (NSInteger i = 0; i < self.columnHeightArray.count; i++) {
CGFloat columnHeight = [self.columnHeightArray[i] doubleValue];
headY = MAX(headY, columnHeight);
}
}
headFrame = CGRectMake(headX, headY, headW, headH);
for (NSInteger i = 0; i < self.columnHeightArray.count; i++) {
self.columnHeightArray[i] = @(CGRectGetMaxY(headFrame));
}
}
// 横向滑动
else {
headH = CGRectGetHeight(self.collectionView.frame);
if (indexPath.section == 0) {
headX = self.edgeInset.left;
} else {
for (NSInteger i = 0; i < self.rowWidthArray.count; i++) {
CGFloat rowWidth = [self.rowWidthArray[i] doubleValue];
headX = MAX(headX, rowWidth);
}
}
headFrame = CGRectMake(headX, headY, headW, headH);
for (NSInteger i = 0; i < self.rowWidthArray.count; i++) {
self.rowWidthArray[i] = @(CGRectGetMaxX(headFrame));
}
}
return headFrame;
}
- (CGRect)footerFrameWithIndexPath:(NSIndexPath *)indexPath {
CGSize footSize = CGSizeZero;
if ([self.delegate respondsToSelector:@selector(flowLayout:sizeForFooterInSection:)]) {
footSize = [self.delegate flowLayout:self sizeForFooterInSection:indexPath.section];
}
CGFloat footX = 0;
CGFloat footY = 0;
CGFloat footW = footSize.width;
CGFloat footH = footSize.height;
CGRect footFrame = CGRectZero;
// 竖向滑动
if (self.scrollDirection == UICollectionViewScrollDirectionVertical) {
footW = CGRectGetWidth(self.collectionView.frame);
for (NSInteger i = 0; i < self.columnHeightArray.count; i++) {
CGFloat columnHeight = [self.columnHeightArray[i] doubleValue];
footY = MAX(footY, columnHeight);
}
footY = footY - self.rowMargin;
footFrame = CGRectMake(footX, footY, footW, footH);
for (NSInteger i = 0; i < self.columnHeightArray.count; i++) {
self.columnHeightArray[i] = @(CGRectGetMaxY(footFrame) + self.edgeInset.top + self.edgeInset.bottom);
}
}
// 横向滑动
else {
footH = CGRectGetHeight(self.collectionView.frame);
for (NSInteger i = 0; i < self.rowWidthArray.count; i++) {
CGFloat rowWidth = [self.rowWidthArray[i] doubleValue];
footX = MAX(footX, rowWidth);
}
footX = footX - self.columnMargin;
footFrame = CGRectMake(footX, footY, footW, footH);
for (NSInteger i = 0; i < self.rowWidthArray.count; i++) {
self.rowWidthArray[i] = @(CGRectGetMaxX(footFrame) + self.edgeInset.left + self.edgeInset.right);
}
}
return footFrame;
}
3、协议方法实现
- (CGFloat)columnMargin {
if ([self.delegate respondsToSelector:@selector(columnMarginInFlowLayout:)]) {
return [self.delegate columnMarginInFlowLayout:self];
}
return 10.0f; // 默认列间距
}
- (CGFloat)rowMargin {
if ([self.delegate respondsToSelector:@selector(rowMarginInFlowLayout:)]) {
return [self.delegate rowMarginInFlowLayout:self];
}
return 10.0f; // 默认行间距
}
- (NSInteger)columnCount {
if ([self.delegate respondsToSelector:@selector(columnCountInFlowLayout:)]) {
return [self.delegate columnCountInFlowLayout:self];
}
return 2; // 默认列数
}
- (NSInteger)rowCount {
if ([self.delegate respondsToSelector:@selector(rowCountInFlowLayout:)]) {
return [self.delegate rowCountInFlowLayout:self];
}
return 1; // 默认行数
}
- (UIEdgeInsets)edgeInset {
if ([self.delegate respondsToSelector:@selector(edgeInsetInFlowLayout:)]) {
return [self.delegate edgeInsetInFlowLayout:self];
}
return UIEdgeInsetsMake(10, 10, 10, 10); // 默认内边距
}
总结
以上就是我对于瀑布流做的一个简单的实现，具体实现见Demo，支持横向滑动和纵向滑动两种布局方式，有兴趣的朋友欢迎留言讨论，大家一起学习