自定义Layout继承UICollectionViewLayout类即可，代码如下：
#import <UIKit/UIKit.h>
@class ZJFallLayout;
@protocol ZJFallLayoutDelegate <NSObject>
@optional
// 列数
-(NSInteger)collectionView:(UICollectionView *)view layout:(ZJFallLayout *)layout columnCountForSectionAtIndex:(NSInteger)section;
// 行间距
-(CGFloat)collectionView:(UICollectionView *)view layout:(ZJFallLayout *)layout lineSpacingForSectionAtIndex:(NSInteger)section;
// 列间距
-(CGFloat)collectionView:(UICollectionView *)view layout:(ZJFallLayout *)layout columnSpacingForSectionAtIndex:(NSInteger)section;
// item大小
-(CGSize)collectionView:(UICollectionView *)view layout:(ZJFallLayout *)layout sizeForItemAtIndexPath:(NSIndexPath *)indexPath;
// 边距
-(UIEdgeInsets)collectionView:(UICollectionView *)view layout:(ZJFallLayout *)layout insetForSectionAtIndex:(NSInteger)section;
@end
@interface ZJFallLayout : UICollectionViewLayout
@property (nonatomic, weak) id<ZJFallLayoutDelegate> delegate;
@end
#import "ZJFallLayout.h"
@interface ZJFallLayout()
///< 所有的cell的布局
@property (nonatomic, strong) NSMutableArray<UICollectionViewLayoutAttributes *> * attrsArray;
///< key列 value maxY值
@property (nonatomic, strong) NSMutableDictionary * columnMaxY;
@end
static const CGFloat ZJDefaultColumnCount = 3; ///< 默认列数
static const CGFloat ZJDefaultColumnMargin = 10; ///< 默认列边距
static const CGFloat ZJDefaultlineMargin = 10; ///< 默认行边距
static const UIEdgeInsets ZJDefaultInsets = {10, 10, 10, 10}; ///< 默认collectionView边距
@implementation ZJFallLayout
- (void)prepareLayout
{
// 重写必须调用super方法
[super prepareLayout];
NSInteger columnCount = [self columnCountWithIndexPath:0];
UIEdgeInsets edgeInsets = [self edgeInsetsWithIndexPath:0];
for(int i=0;i<columnCount;i++){
NSString * columKey = [NSString stringWithFormat:@"%d",i];
[[self columnMaxY] setValue:@(edgeInsets.top) forKey:columKey];
}
// 遍历所有的cell，计算所有cell的布局
[[self attrsArray] removeAllObjects];
for (NSInteger i = 0; i < [self.collectionView numberOfItemsInSection:0]; i++) {
NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0];
// 计算布局属性并将结果添加到布局属性数组中
@autoreleasepool{
[self.attrsArray addObject:[self layoutAttributesForItemAtIndexPath:indexPath]];
}
}
//NSLog(@" > > > > > > > ");
}
// 返回布局属性，一个UICollectionViewLayoutAttributes对象数组
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
return self.attrsArray;
}
//设置collectionView滚动区域
-(CGSize)collectionViewContentSize
{
//假设最长的那一列为第0列
__block NSString *maxColumn = @"0";
//遍历字典,找出最长的那一列
[self.columnMaxY enumerateKeysAndObjectsUsingBlock:^(NSString *column, NSNumber *maxY, BOOL *stop) {
if ([maxY floatValue] > [self.columnMaxY[maxColumn] floatValue])
{
maxColumn = column;
}
}];
return CGSizeMake(0, [self.columnMaxY[maxColumn]floatValue]);
}
//允许每一次重新布局
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
return YES;
}
-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewLayoutAttributes * attLayout = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
// 取出Y值最小的列
NSString * minYColumKey = @"0";
for(NSString * columKey in [[self columnMaxY] allKeys]){
CGFloat maxY = [[[self columnMaxY] objectForKey:columKey] doubleValue];
if([[[self columnMaxY] objectForKey:minYColumKey] doubleValue] > maxY){
minYColumKey = columKey;
}
}
CGSize itemSize = [self itemSizeWithIndexPath:indexPath];
UIEdgeInsets edgeInsets = [self edgeInsetsWithIndexPath:indexPath];
CGFloat columnSpacing = [self columnSpacingWithIndexPath:indexPath];
CGFloat lineSpacing = [self lineSpacingWithIndexPath:indexPath];
CGFloat x = edgeInsets.left+(itemSize.width+columnSpacing)*[minYColumKey intValue];
CGFloat y = [[[self columnMaxY] objectForKey:minYColumKey] doubleValue];
[[self columnMaxY] setValue:@(y+lineSpacing+itemSize.height) forKey:minYColumKey];
CGRect newFrame = CGRectMake(x, y, itemSize.width, itemSize.height);
[attLayout setFrame:newFrame];
return attLayout;
}
-(NSMutableArray<UICollectionViewLayoutAttributes *> *)attrsArray{
if(!_attrsArray){
_attrsArray = [NSMutableArray array];
}
return _attrsArray;
}
- (NSMutableDictionary *)columnMaxY{
if(!_columnMaxY){
_columnMaxY = [NSMutableDictionary dictionary];
}
return _columnMaxY;
}
- (CGFloat)columnCountWithIndexPath:(NSIndexPath*)indexPath
{
if([self delegate] && [[self delegate] respondsToSelector:@selector(collectionView:layout:columnCountForSectionAtIndex:)]){
return [[self delegate] collectionView:[self collectionView] layout:self columnCountForSectionAtIndex:indexPath.section];
}else{
return ZJDefaultColumnCount;
}
}
- (CGFloat)lineSpacingWithIndexPath:(NSIndexPath*)indexPath
{
if([self delegate] && [[self delegate] respondsToSelector:@selector(collectionView:layout:lineSpacingForSectionAtIndex:)]){
return [[self delegate] collectionView:[self collectionView] layout:self lineSpacingForSectionAtIndex:indexPath.section];
}else{
return ZJDefaultlineMargin;
}
}
- (CGFloat)columnSpacingWithIndexPath:(NSIndexPath*)indexPath
{
if([self delegate] && [[self delegate] respondsToSelector:@selector(collectionView:layout:columnSpacingForSectionAtIndex:)])
{
return [[self delegate] collectionView:[self collectionView] layout:self columnSpacingForSectionAtIndex:indexPath.section];
}else{
return ZJDefaultColumnMargin;
}
}
- (UIEdgeInsets)edgeInsetsWithIndexPath:(NSIndexPath*)indexPath
{
if([self delegate] && [[self delegate] respondsToSelector:@selector(collectionView:layout:insetForSectionAtIndex:)]){
return [[self delegate] collectionView:[self collectionView] layout:self insetForSectionAtIndex:indexPath.section];
}else{
return ZJDefaultInsets;
}
}
-(CGSize)itemSizeWithIndexPath:(NSIndexPath*)indexPath{
if([self delegate] && [[self delegate] respondsToSelector:@selector(collectionView:layout:sizeForItemAtIndexPath:)]){
return [[self delegate] collectionView:[self collectionView] layout:self sizeForItemAtIndexPath:indexPath];
}else{
CGFloat width = CGRectGetWidth([[self collectionView] frame]);
UIEdgeInsets edgeInsets = [self edgeInsetsWithIndexPath:indexPath];
CGFloat columnSpacing = [self columnSpacingWithIndexPath:indexPath];
NSInteger columnCount = [self columnCountWithIndexPath:indexPath];
CGFloat cellW = (width - edgeInsets.left - edgeInsets.right -
columnSpacing * (columnCount - 1)) / columnCount;
return CGSizeMake(cellW, cellW);
}
}
@end