瀑布流的核心算法

瀑布流的核心算法原理

123.png

上图所显示就是瀑布流做出来的。定义了3列图片，
第0张图片将要加到视图中时，程序就会自动寻找第几列的高度最短并将第0张图片，如果一样就优先最左边的，并且更新最短那列的高度。以此类推就可以形成以上图一样的程序出来。

下面是瀑布流核心计算的方法代码

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #008400}p.p3 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #703daa}p.p4 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; min-height: 13.0px}p.p5 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo; color: #31595d}p.p6 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px 'PingFang SC'; color: #008400}span.s1 {font-variant-ligatures: no-common-ligatures}span.s2 {font-variant-ligatures: no-common-ligatures; color: #703daa}span.s3 {font-variant-ligatures: no-common-ligatures; color: #000000}span.s4 {font: 11.0px 'PingFang SC'; font-variant-ligatures: no-common-ligatures}span.s5 {font-variant-ligatures: no-common-ligatures; color: #3d1d81}span.s6 {font-variant-ligatures: no-common-ligatures; color: #bb2ca2}span.s7 {font-variant-ligatures: no-common-ligatures; color: #31595d}span.s8 {font-variant-ligatures: no-common-ligatures; color: #272ad8}span.s9 {font-variant-ligatures: no-common-ligatures; color: #4f8187}span.s10 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures; color: #000000}span.s11 {font: 11.0px Menlo; font-variant-ligatures: no-common-ligatures}

- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    // 创建布局属性
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    
    // collectionView的宽度
    CGFloat collectionViewW = self.collectionView.frame.size.width;
    
    // 设置布局属性的frame
    CGFloat w = (collectionViewW - self.edgeInsets.left - self.edgeInsets.right - (self.columnCount - 1) * self.columnMargin) / self.columnCount;
    CGFloat h = [self.delegate waterflowLayout:self heightForItemAtIndex:indexPath.item itemWidth:w];
    
    // 找出高度最短的那一列
    NSInteger destColumn = 0;
    CGFloat minColumnHeight = [self.columnHeights[0] doubleValue];
    for (NSInteger i = 1; i < self.columnCount; i++) {
        // 取得第i列的高度
        CGFloat columnHeight = [self.columnHeights[i] doubleValue];
        
        if (minColumnHeight > columnHeight) {
            minColumnHeight = columnHeight;
            destColumn = i;
        }
    }
    
    CGFloat x = self.edgeInsets.left + destColumn * (w + self.columnMargin);
    CGFloat y = minColumnHeight;
    if (y != self.edgeInsets.top) {
        y += self.rowMargin;
    }
    attrs.frame = CGRectMake(x, y, w, h);
    
    // 更新最短那列的高度
    self.columnHeights[destColumn] = @(CGRectGetMaxY(attrs.frame));
    
    // 记录内容的高度
    CGFloat columnHeight = [self.columnHeights[destColumn] doubleValue];
    if (self.contentHeight < columnHeight) {
        self.contentHeight = columnHeight;
    }
    return attrs;
}