我们有时候会遇到这样的情形，就是需要展示一些动态的标签，宽度是动态的，
水平方向是一行，其实这种情况还是比较容易处理的，只是一下子想不起来，
这里做了一个相关的需求，将思路和代码记录下来，方便后续的查找
效果图
思路：就是重写自定义layout的prepare layout 方法， 在里面计算每一个item 的frame
。通过[UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:[NSIndexPath indexPathForItem:i inSection:0]] 方法创建 UICollectionViewLayoutAttributes 对象，然后个UICollectionViewLayoutAttributes 对象的frame赋值，这里要记录上一个UICollectionViewLayoutAttributes对象的x.及总的宽度。通过这句代码赋值frame
layoutAttributes.frame = CGRectMake(currentX, currentY, cellWidth, cellHeight);
然后将布局属性添加到一个数组中
在layoutAttributesForElementsInRect:方法中返回数组。
在 collectionViewContentSize 方法中返回宽度
还有一点，我们需要通过代理方式获取到单个item的宽度
-
(CGFloat)cellWidthForItemAtIndex:(NSInteger)index;
-
(CGFloat)footerWidthForFooterAtSection:(NSInteger)section;
代码
@protocol LIUNumberCenterAssociationLayoutDelegate <NSObject>- (CGFloat)cellWidthForItemAtIndex:(NSInteger)index;- (CGFloat)footerWidthForFooterAtSection:(NSInteger)section;@end@interface LIUNumberCenterAssociationLayout : UICollectionViewFlowLayout@property (nonatomic, weak) id <LIUNumberCenterAssociationLayoutDelegate> delegate;@end
//
// LIUNumberCenterAssociationLayout.m
//#import "LIUNumberCenterAssociationLayout.h"@interface LIUNumberCenterAssociationLayout ()@property (nonatomic, strong) NSMutableArray<UICollectionViewLayoutAttributes *> *layoutAttributesArray;@property (nonatomic, assign) CGSize contentSize;@end@implementation LIUNumberCenterAssociationLayout- (instancetype)init {if (self = [super init]) {self.layoutAttributesArray = [NSMutableArray new];self.contentSize = CGSizeMake(16, 22); // 16是左边距}return self;
}- (void)prepareLayout {[super prepareLayout];[self updateLayout];
}- (CGSize)collectionViewContentSize {return self.contentSize;
}- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect {return self.layoutAttributesArray;
}#pragma mark - ---------- update ----------- (void)updateLayout {// 移除旧的布局[self.layoutAttributesArray removeAllObjects];self.contentSize = CGSizeMake(8, 28); // 16是左边距// 计算新的布局NSInteger count = 0;if ([self.collectionView.dataSource respondsToSelector:@selector(collectionView:numberOfItemsInSection:)]) {count = [self.collectionView.dataSource collectionView:self.collectionView numberOfItemsInSection:0];}CGFloat x = 0; if (count > 0) {for (int i = 0; i < count; i++) {CGFloat currentX = x;CGFloat currentY = 0;CGFloat cellWidth = [self cellWidthForItemAtIndex:i];CGFloat cellHeight = 28;// 创建布局属性UICollectionViewLayoutAttributes *layoutAttributes = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];layoutAttributes.frame = CGRectMake(currentX, currentY, cellWidth, cellHeight);[self.layoutAttributesArray addObject:layoutAttributes];// 计算下一个item的x，以及布局更新结束检测if (i < count - 1) {x = currentX + cellWidth + 8; // 8是间距} else {x = currentX + cellWidth + 8; // 8是右边距self.contentSize = CGSizeMake(x, 0);}}}if ([self.delegate respondsToSelector:@selector(footerWidthForFooterAtSection:)]) {CGFloat footerWidth = [self.delegate footerWidthForFooterAtSection:0];UICollectionViewLayoutAttributes *layoutattribute = [UICollectionViewLayoutAttributes layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter withIndexPath:[NSIndexPath indexPathForItem:0 inSection:0]];layoutattribute.frame = CGRectMake(x, 0, footerWidth, 28);x += footerWidth ;self.contentSize = CGSizeMake(x, 28);[self.layoutAttributesArray addObject:layoutattribute];}
}- (CGFloat)cellWidthForItemAtIndex:(NSInteger)index {CGFloat width = 0;if ([self.delegate respondsToSelector:@selector(cellWidthForItemAtIndex:)]) {width = [self.delegate cellWidthForItemAtIndex:index];}return width;
}@end