版权声明：本文为Trinity原创文章，未经Trinity允许不得转载 https://blog.csdn.net/Caoyang_He/article/details/87983250
上学期进行了一次swift实训，组里的小姐姐们说能不能用瀑布流的效果，开始我以为和通讯录那种行表式差不多，查看xcode里面有没有支持这种效果的方法，但是找了很久没有找到。于是准备自己动手，code了一天，但是还是没有弄出来，在组里大佬的提醒下，我意识到我没有必要自己造轮子，可以用别人写好的。于是推荐了我一个很好的网站：代码库，里面有许多别人做好的案例。
于是我开始进行搜索瀑布流相关的代码，但是我下载了许多来运行的时候发现有许多是object-C来写，和swfit混用有点让人难受。当我找到一些用swfit写的瀑布流案例后，发现有些代码逻辑太乱，有些又写的很复杂，好不容易遇到一个注释清晰的，但是不能实现我想要实现的效果。最后找到了一个可塑性较好的瀑布流代码（代码链接）
我想要的几个特点是：
- 最基本的瀑布流效果
- 可以有多列，至少要有两列
- 每个cell里面的图片可以自适应（这个就是自己写的）
基本代码如下：
WCLWaterFallLayout.swift
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 = 20
//列间距
@IBInspectable var columnSpacing: CGFloat = 20
//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
}
}
代码流畅，注释清晰
接着就是应用部分主要是以下部分代码
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
imageindex = indexPath.row
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if miaoshu.count > imagenames.count
{
return imagenames.count
}
else
{
//return (miaoshu1?.count)!
return miaoshu.count
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Identifier", for: indexPath)
let color = UIColor.init(red: 255.0/255.0, green: 204.0/255.0, blue: 204.0/255.0, alpha: 0.5)
cell.contentView.backgroundColor = color
//let imagename = "p"+String(indexPath.row % 6+1)
// imagename = String(indexPath.row % 11+1)
if imageget != nil && indexPath.row == 0
{
image = imageget
}
else
{
imagename = imagenames[indexPath.row ]
image = UIImage(named: imagename)
}
let imageheight = image?.size.height
let imagewidth = image?.size.width
let rate = imagewidth! / imageheight!
let height = self.collectionView.bounds.width / rate
let imageView = UIImageView(frame: CGRect(x:0, y: 1, width: self.collectionView.bounds.width/2-5, height: (height)/2))
imageView.image = image
imageView.layer.cornerRadius = 10
imageView.layer.masksToBounds = true
cell.contentView.addSubview(imageView)
let labelName = UILabel(frame: CGRect(x: 0,y:height/2 + 10 , width: self.collectionView.bounds.width/2-5, height: 20))
if miaoshuget != "" && indexPath.row == 0
{
labelName.text = self.miaoshuget
}
else
{
labelName.text = miaoshu[indexPath.row ]
}
labelName.textAlignment = .center
labelName.font = UIFont.systemFont(ofSize: 20)
cell.contentView.addSubview(labelName)
cell.contentView.clipsToBounds = true
cell.contentView.layer.cornerRadius = 8
return cell
}
func columnOfWaterFall(_ collectionView: UICollectionView) -> Int {
return columnCount
}
func waterFall(_ collectionView: UICollectionView, layout waterFallLayout: WCLWaterFallLayout, heightForItemAt indexPath: IndexPath) -> CGFloat {
//image = UIImage(named: String(indexPath.row % 11+1))
if imageget != nil && indexPath.row == 0
{
image = imageget
}
else
{
image = UIImage(named: imagenames[indexPath.row ])
}
let imageheight = image?.size.height
let imagewidth = image?.size.width
let rate = imagewidth! / imageheight!
let height = (self.collectionView.bounds.width / rate ) / 2 + 40
return CGFloat(height)
}
关于图片自适应的思路：首先以两列的瀑布流来看，由于列数固定，那么每个cell的宽width应该是一样的，要想每个cell里面的图片不失真（压缩或者拉伸），应该根据图片的的宽和高的比例来对应设置每个cell的高hight，于是得到一个表达式：cell_hight/cell_width=image_hight/image_wight，通过以上表达式就可以完成图片自适应的效果