iOS 瀑布流的简单实现 UICollectionView
lllaaggo
9年前
来自: http://www.cnblogs.com/tanhui/p/5160850.html
UICollectionView 瀑布流的简单实现
UICollectionView 比 tableView 灵活,功能也强大很多。系统实现了流式布局,但用处还有很多限制。
要想实现更灵活的布局,就咬重写UICollectionViewLayout。
Demo地址: WaterfallCollectionLayout
先看下实现效果:
废话不多说,直接上代码:
先看WaterfallCollectionLayout.m
#import "WaterfallCollectionLayout.h" #define colMargin 5 #define colCount 4 #define rolMargin 5 @interface WaterfallCollectionLayout () //数组存放每列的总高度 @property(nonatomic,strong)NSMutableArray* colsHeight; //单元格宽度 @property(nonatomic,assign)CGFloat colWidth; @end
该类要重写以下方法:
//完成布局前的初始工作 -(void)prepareLayout; //collectionView的内容尺寸 -(CGSize)collectionViewContentSize; //为每个item设置属性 -(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath; //获取制定范围的所有item的属性 -(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect; -(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds;
每次调用会清空colsHeight数组里的信息:
//完成布局前的初始工作 -(void)prepareLayout{ [super prepareLayout]; self.colWidth =( self.collectionView.frame.size.width - (colCount+1)*colMargin )/colCount; //让它重新加载 self.colsHeight = nil; }
通过遍历colHeight数组里的所有列来获得最长的那一列,返回contentsize
//collectionView的内容尺寸 -(CGSize)collectionViewContentSize{ NSNumber * longest = self.colsHeight[0]; for (NSInteger i =0;i<self.colsHeight.count;i++) { NSNumber* rolHeight = self.colsHeight[i]; if(longest.floatValue<rolHeight.floatValue){ longest = rolHeight; } } return CGSizeMake(self.collectionView.frame.size.width, longest.floatValue); }
每个cell要出来时这个方法会被调用,在此方法中设置该cell的frame。
注意heightBlock是外部控制器传进来的block用以计算每个cell的高度,现在我只是设置了随机数。如果没有传block进来我这里直接让他崩溃了。
//为每个item设置属性 -(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath{ UICollectionViewLayoutAttributes* attr = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath]; NSNumber * shortest = self.colsHeight[0]; NSInteger shortCol = 0; for (NSInteger i =0;i<self.colsHeight.count;i++) { NSNumber* rolHeight = self.colsHeight[i]; if(shortest.floatValue>rolHeight.floatValue){ shortest = rolHeight; shortCol=i; } } CGFloat x = (shortCol+1)*colMargin+ shortCol * self.colWidth; CGFloat y = shortest.floatValue+colMargin; //获取cell高度 CGFloat height=0; NSAssert(self.heightBlock!=nil, @"未实现计算高度的block "); if(self.heightBlock){ height = self.heightBlock(indexPath); } attr.frame= CGRectMake(x, y, self.colWidth, height); self.colsHeight[shortCol]=@(shortest.floatValue+colMargin+height); return attr; }
//获取所有item的属性 -(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{ NSMutableArray* array = [NSMutableArray array]; NSInteger items = [self.collectionView numberOfItemsInSection:0]; for (int i = 0; i<items;i++) { UICollectionViewLayoutAttributes* attr = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]]; [array addObject:attr]; } return array; }
实现下列方法会在出现新的cell时重新布局并调用preparelayout方法
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds{ return YES; }
每列高度的存放,初始高度可以改,我这里是0
-(NSMutableArray *)colsHeight{ if(!_colsHeight){ NSMutableArray * array = [NSMutableArray array]; for(int i =0;i<colCount;i++){ //这里可以设置初始高度 [array addObject:@(0)]; } _colsHeight = [array mutableCopy]; } return _colsHeight; }
再来看看控制器里就是这么简单
#pragma mark getter-setter -(UICollectionView *)collectionView{ if(!_collectionView){ _collectionView = [[UICollectionView alloc]initWithFrame:self.view.frame collectionViewLayout:self.layout]; _collectionView.backgroundColor = [UIColor whiteColor]; _collectionView.delegate=self; _collectionView.dataSource=self; [_collectionView registerClass:[CollectionViewCell class] forCellWithReuseIdentifier:identifer]; } return _collectionView; } -(UICollectionViewLayout *)layout{ if(!_layout){ _layout = [[WaterfallCollectionLayout alloc]initWithItemsHeightBlock:^CGFloat(NSIndexPath *index) { return [self.heightArr[index.item] floatValue]; }]; } return _layout; } -(NSArray *)heightArr{ if(!_heightArr){ //随机生成高度 NSMutableArray *arr = [NSMutableArray array]; for (int i = 0; i<100; i++) { [arr addObject:@(arc4random()%50+80)]; } _heightArr = [arr copy]; } return _heightArr; }