iOS之瀑布流布局设计

#import "CXDWaterflowLayout.h"

/** 默认的列数 */
static const NSInteger CXDDefaultColumnCount = 3;
/** 每一列之间的间距 */
static const CGFloat CXDDefaultColumnMargin = 10;
/** 每一行之间的间距 */
static const CGFloat CXDDefaultRowMargin = 10;
/** 边缘间距 */
static const UIEdgeInsets CXDDefaultEdgeInsets = {10, 10, 10, 10};

@interface CXDWaterflowLayout()
/** 存放所有cell的布局属性 */
@property (nonatomic, strong) NSMutableArray *attrsArray;
/** 存放所有列的当前高度 */
@property (nonatomic, strong) NSMutableArray *columnHeights;
@end

@implementation CXDWaterflowLayout

- (NSMutableArray *)columnHeights
{
if (!_columnHeights) {
_columnHeights = [NSMutableArray array];
}
return _columnHeights;
}

- (NSMutableArray *)attrsArray
{
if (!_attrsArray) {
_attrsArray = [NSMutableArray array];
}
return _attrsArray;
}

/**
* 初始化
*/
- (void)prepareLayout
{
[super prepareLayout];

// 清除以前计算的所有高度
[self.columnHeights removeAllObjects];
for (NSInteger i = 0; i < CXDDefaultColumnCount; i++) {
[self.columnHeights addObject:@(CXDDefaultEdgeInsets.top)];
}

// 清除之前所有的布局属性
[self.attrsArray removeAllObjects];
// 开始创建每一个cell对应的布局属性
NSInteger count = [self.collectionView numberOfItemsInSection:0];
for (NSInteger i = 0; i < count; i++) {
// 创建位置
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
// 获取indexPath位置cell对应的布局属性
UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:indexPath];
[self.attrsArray addObject:attrs];
}
}

/**
* 决定cell的排布
*/
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
return self.attrsArray;
}

/**
* 返回indexPath位置cell对应的布局属性
*/
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
// 创建布局属性
UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

// collectionView的宽度
CGFloat collectionViewW = self.collectionView.frame.size.width;

// 设置布局属性的frame
CGFloat w = (collectionViewW - CXDDefaultEdgeInsets.left - CXDDefaultEdgeInsets.right - (CXDDefaultColumnCount - 1) * CXDDefaultColumnMargin) / CXDDefaultColumnCount;
CGFloat h = 50 + arc4random_uniform(100);

// 找出高度最短的那一列
NSInteger destColumn = 0;
CGFloat minColumnHeight = [self.columnHeights[0] doubleValue];
for (NSInteger i = 1; i < CXDDefaultColumnCount; i++) {
// 取得第i列的高度
CGFloat columnHeight = [self.columnHeights[i] doubleValue];

if (minColumnHeight > columnHeight) {
minColumnHeight = columnHeight;
destColumn = i;
}
}

CGFloat x = CXDDefaultEdgeInsets.left + destColumn * (w + CXDDefaultColumnMargin);
CGFloat y = minColumnHeight;
if (y != CXDDefaultEdgeInsets.top) {
y += CXDDefaultRowMargin;
}
attrs.frame = CGRectMake(x, y, w, h);

// 更新最短那列的高度
self.columnHeights[destColumn] = @(CGRectGetMaxY(attrs.frame));

return attrs;
}

- (CGSize)collectionViewContentSize
{
CGFloat maxColumnHeight = [self.columnHeights[0] doubleValue];
for (NSInteger i = 1; i < CXDDefaultColumnCount; i++) {
// 取得第i列的高度
CGFloat columnHeight = [self.columnHeights[i] doubleValue];

if (maxColumnHeight < columnHeight) {
maxColumnHeight = columnHeight;
}
}
return CGSizeMake(0, maxColumnHeight + CXDDefaultEdgeInsets.bottom);
}

@end