iOS 瀑布流的简单实现 UICollectionView

lllaaggo 8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;  }