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最近项目中需要用到瀑布流的效果，但是用uicollectionviewflowlayout又达不到效果，自己动手写了一个瀑布流的layout，下面是我的心路路程
先上效果图与demo地址：
因为是用uicollectionview来实现瀑布流的，决定继承uicollectionviewlayout来自定义一个layout来实现一个简单瀑布流的布局，下面是需要重写的方法：
重写这个属性得出uicollectionview的contentsize：collectionviewcontentsize
重写这个方法来得到每个item的布局：layoutattributesforitem(at indexpath: indexpath) -> uicollectionviewlayoutattributes?
重写这个方法给uicollectionview所有item的布局：layoutattributesforelements(in rect: cgrect) -> [uicollectionviewlayoutattributes]?
重写这个方法来实现uicollectionview前的操作：prepare()
实现思路
通过代理模式获得到需要的列数和每一item的高度，用过列数与列之间的间隔和uicollectionview的宽度来得出每一列的宽度，item从左边到右布局，下一列的item放到高度最小的列下面，防止每列的高度不均匀，下面贴上代码和注释：
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import uikit
@objc protocol wclwaterfalllayoutdelegate {
//waterfall的列数
func columnofwaterfall(_ collectionview: uicollectionview) -> int
//每个item的高度
func waterfall(_ collectionview: uicollectionview, layout waterfalllayout: wclwaterfalllayout, heightforitemat indexpath: indexpath) -> cgfloat
}
class wclwaterfalllayout: uicollectionviewlayout {
//代理
weak var delegate: wclwaterfalllayoutdelegate?
//行间距
@ibinspectable var linespacing: cgfloat = 0
//列间距
@ibinspectable var columnspacing: cgfloat = 0
//section的top
@ibinspectable var sectiontop: cgfloat = 0 {
willset {
sectioninsets.top = newvalue
}
}
//section的bottom
@ibinspectable var sectionbottom: cgfloat = 0 {
willset {
sectioninsets.bottom = newvalue
}
}
//section的left
@ibinspectable var sectionleft: cgfloat = 0 {
willset {
sectioninsets.left = newvalue
}
}
//section的right
@ibinspectable var sectionright: cgfloat = 0 {
willset {
sectioninsets.right = newvalue
}
}
//section的insets
@ibinspectable var sectioninsets: uiedgeinsets = uiedgeinsets.zero
//每行对应的高度
private var columnheights: [int: cgfloat] = [int: cgfloat]()
private var attributes: [uicollectionviewlayoutattributes] = [uicollectionviewlayoutattributes]()
//mark: initial methods
init(linespacing: cgfloat, columnspacing: cgfloat, sectioninsets: uiedgeinsets) {
super.init()
self.linespacing = linespacing
self.columnspacing = columnspacing
self.sectioninsets = sectioninsets
}
required init?(coder adecoder: nscoder) {
super.init(coder: adecoder)
}
//mark: public methods
//mark: override
override var collectionviewcontentsize: cgsize {
var maxheight: cgfloat = 0
for height in columnheights.values {
if height > maxheight {
maxheight = height
}
}
return cgsize.init(width: collectionview?.frame.width ?? 0, height: maxheight + sectioninsets.bottom)
}
override func prepare() {
super.prepare()
guard collectionview != nil else {
return
}
if let columncount = delegate?.columnofwaterfall(collectionview!) {
for i in 0..<columncount {
columnheights[i] = sectioninsets.top
}
}
let itemcount = collectionview!.numberofitems(insection: 0)
attributes.removeall()
for i in 0..<itemcount {
if let att = layoutattributesforitem(at: indexpath.init(row: i, section: 0)) {
attributes.append(att)
}
}
}
override func layoutattributesforitem(at indexpath: indexpath) -> uicollectionviewlayoutattributes? {
if let collectionview = collectionview {
//根据indexpath获取item的attributes
let att = uicollectionviewlayoutattributes.init(forcellwith: indexpath)
//获取collectionview的宽度
let width = collectionview.frame.width
if let columncount = delegate?.columnofwaterfall(collectionview) {
guard columncount > 0 else {
return nil
}
//item的宽度 = (collectionview的宽度 - 内边距与列间距) / 列数
let totalwidth = (width - sectioninsets.left - sectioninsets.right - (cgfloat(columncount) - 1) * columnspacing)
let itemwidth = totalwidth / cgfloat(columncount)
//获取item的高度，由外界计算得到
let itemheight = delegate?.waterfall(collectionview, layout: self, heightforitemat: indexpath) ?? 0
//找出最短的那一列
var minindex = 0
for column in columnheights {
if column.value < columnheights[minindex] ?? 0 {
minindex = column.key
}
}
//根据最短列的列数计算item的x值
let itemx = sectioninsets.left + (columnspacing + itemwidth) * cgfloat(minindex)
//item的y值 = 最短列的最大y值 + 行间距
let itemy = (columnheights[minindex] ?? 0) + linespacing
//设置attributes的frame
att.frame = cgrect.init(x: itemx, y: itemy, width: itemwidth, height: itemheight)
//更新字典中的最大y值
columnheights[minindex] = att.frame.maxy
}
return att
}
return nil
}
override func layoutattributesforelements(in rect: cgrect) -> [uicollectionviewlayoutattributes]? {
return attributes
}
}
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最后附带demo地址，大家喜欢的话可以star一下
上面是简单的瀑布流的实现过程，希望大家能学到东西，有很多地方考虑的不足，欢迎大家交流学习，谢谢大家的阅读。