UICollectionView

瀑布流实现思路

• 创建collectionView，设置代理，注册cell

    // 创建布局
    WZWaterfallLayout *layout = [[WZWaterfallLayout alloc] init];
    // 设置代理
    layout.delegate = self;
  
    //创建collectionView
    UICollectionView *collectionView = [[UICollectionView alloc] initWithFrame:self.view.bounds collectionViewLayout:layout];
    collectionView.backgroundColor = [UIColor whiteColor];
    collectionView.dataSource = self;
    [self.view addSubview:collectionView];
  

• 自定义布局，继承自纯净的UICollectionViewLayout

  • 准备布局

/**
 * 准备布局
 */
- (void)prepareLayout
{
    [super prepareLayout];

    // 初始化内容高度的变量
    self.contentHeight = 0;

    // 先移除之前的所有列数的高度数组
    [self.colHeights removeAllObjects];
    for (NSInteger i = 0 ; i < self.colCount; i++) {
        // 初始化，赋值为一个顶部的类边距
        [self.colHeights addObject:@(self.edgeInsets.top)];
    }

    // 清除之前所有布局属性的数组
    [self.attriArrM removeAllObjects];
    // collectionView第0组的所有元素
    NSInteger count = [self.collectionView numberOfItemsInSection:0];

    for (NSInteger i = 0; i < count; i++) {

        NSIndexPath *indexPath = [NSIndexPath indexPathForItem:i inSection:0] ;

        UICollectionViewLayoutAttributes *attr = [self layoutAttributesForItemAtIndexPath:indexPath];

        [self.attriArrM addObject:attr];
    }
}

• 需要哪些布局

/**
 * 返回全部的布局
 */
- (NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect
{
    return self.attriArrM;
}

• 具体布局属性

/**
 * 返回全部的布局属性
 */
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes *attr = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];

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

    // cell的尺寸
    CGFloat w = (collectionW - self.edgeInsets.left - self.edgeInsets.right - (self.colCount - 1) * self.colMargin ) / self.colCount;
    CGFloat h = [self.delegate WaterfallLayout:self heightForItemRowAtIndex:indexPath.item width:w];

    // 最短的一列
    NSInteger dustCol = 0;
    // 取出第0列的高度
    CGFloat minColHeight = [self.colHeights[0] doubleValue];

    for (NSInteger i = 1; i < self.colCount; i++) {
        // 第0列大于下一列
        if (minColHeight > [self.colHeights[i] doubleValue]) {
            minColHeight = [self.colHeights[i] doubleValue];
            dustCol = i;
        }
    }

    // cell的位置
    CGFloat x = dustCol * (w + self.colCount) + self.edgeInsets.left;
    CGFloat y = minColHeight;
    if (y != self.edgeInsets.top) {
        y += self.rowMargin;
    }

    // 设置cell的frame
    attr.frame = CGRectMake(x, y, w, h);

    // 更新当前列的高度
    self.colHeights[dustCol] = @(CGRectGetMaxY(attr.frame));

    // 当前列高度
    CGFloat colHeight = [self.colHeights[dustCol] doubleValue];
    // 当前列高度大于之前的内容高度
    if (self.contentHeight < colHeight) {
        // 赋值
        self.contentHeight = colHeight;
    }

    return attr;
}

• 设置内容尺寸

/**
 * 返回内容尺寸
 */
- (CGSize)collectionViewContentSize
{
    return CGSizeMake(0, self.contentHeight + self.edgeInsets.bottom);
}

• 注册cell，实现代理方法

 // 注册cell
    [collectionView registerNib:[UINib nibWithNibName:NSStringFromClass([WZShopCell class]) bundle:nil] forCellWithReuseIdentifier:WZCellId];
    self.collectionView = collectionView;

#pragma mark - <UICollectionViewDataSource>
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    self.collectionView.footer.hidden = !self.shops.count;
    return self.shops.count;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    WZShopCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:WZCellId forIndexPath:indexPath];
    // 传递模型
    cell.shop = self.shops[indexPath.item];

    return cell;
}

• 实现自定义布局的代理方法

#pragma mark - <XMGWaterflowLayoutDelegate>
- (CGFloat)waterflowLayout:(XMGWaterflowLayout *)waterflowLayout heightForItemAtIndex:(NSUInteger)index itemWidth:(CGFloat)itemWidth
{
    XMGShop *shop = self.shops[index];

    return itemWidth * shop.h / shop.w;
}

- (CGFloat)rowMarginInWaterflowLayout:(XMGWaterflowLayout *)waterflowLayout
{
    return 20;
}

- (CGFloat)columnCountInWaterflowLayout:(XMGWaterflowLayout *)waterflowLayout
{
    if (self.shops.count <= 50) return 2;
    return 3;
}

- (UIEdgeInsets)edgeInsetsInWaterflowLayout:(XMGWaterflowLayout *)waterflowLayout
{
    return UIEdgeInsetsMake(10, 20, 30, 100);
}