这段时间突然想到一个很久之前用到的知识-瀑布流,本来想用一个简单的方法,发现自己走入了歧途,最终只能狠下心来重写UICollectionViewFlowLayout.下面我将用两种方法实现瀑布流,以及会介绍第一种实现的bug.
<1>第一种
效果图如下所示:
这种实现方法的思路:
1)首先调用随机函数,产生随机高度,并把它保存到数组中
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGFloat cellW = ;
CGFloat cellH = + (arc4random() % );
[self.heightArrayM addObject:@(cellH)];
return CGSizeMake(cellW, cellH);
}
2)在设置cell的frame的地方,通过取余,取整确定cell的高度,并设定cell的frame
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:ID forIndexPath:indexPath];
//当前处于多少行
NSInteger num1 = indexPath.row / count;
//当前处于多少列
int num2 = indexPath.row % count;
CGFloat cellX = num2 * + (num2 + ) * margin;
CGFloat cellY = ;
for (int i = ; i < num1; i++) {
NSInteger position = num2 + i * ;
cellY += [self.heightArrayM[position] floatValue] + margin;
}
CGFloat cellW = ;
CGFloat cellH = cellHeight;
cell.frame = CGRectMake(cellX, cellY, cellW, cellH);
// cell.backgroundColor = [UIColor redColor];
cell.backgroundColor = [UIColor colorWithRed:(arc4random() % ) / 250.0 green:(arc4random() % ) / 250.0 blue:(arc4random() % ) / 250.0 alpha:1.0];
// NSLog(@"%@", NSStringFromCGRect(cell.frame));
return cell;
}
弊端 : 其实这种方法的弊端,相信从上面的动态图中可以看出来,当往上面滑的时候,由于cell的循环机制,下面的cell的会消失,但是由于高度不一致,同时撤销的是最后一行的cell,所以下面的cell在屏幕上就会消失.
下面附上第一种方法的源代码:
#import "ViewController.h" #define margin 10
#define count 3
#define cellHeight [self.heightArrayM[indexPath.row] floatValue]
static NSString * const ID = @"cell";
@interface ViewController ()<UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout>
@property (weak, nonatomic) IBOutlet UICollectionView *collectionView;
@property (nonatomic, strong) NSMutableArray *heightArrayM; @end @implementation ViewController - (NSMutableArray *)heightArrayM {
if (_heightArrayM == nil) {
_heightArrayM = [NSMutableArray array];
}
return _heightArrayM;
} - (void)viewDidLoad {
[super viewDidLoad]; [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:ID];
self.collectionView.dataSource = self;
self.collectionView.delegate = self;
//设置collectionView
[self setupCollectionView];
} //设置collectionView的布局
- (UICollectionViewFlowLayout *)setupCollectionLayout {
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init]; flowLayout.minimumInteritemSpacing = margin;
flowLayout.minimumLineSpacing = margin;
flowLayout.sectionInset = UIEdgeInsetsMake(margin, margin, margin, margin);
return flowLayout;
} //设置collectionView
- (void)setupCollectionView {
self.collectionView.collectionViewLayout =[self setupCollectionLayout]; } #pragma mark - UICollectionViewDataSouce
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return ;
} - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { UICollectionViewCell *cell = [self.collectionView dequeueReusableCellWithReuseIdentifier:ID forIndexPath:indexPath];
//当前处于多少行
NSInteger num1 = indexPath.row / count;
//当前处于多少列
int num2 = indexPath.row % count;
CGFloat cellX = num2 * + (num2 + ) * margin;
CGFloat cellY = ;
for (int i = ; i < num1; i++) {
NSInteger position = num2 + i * ;
cellY += [self.heightArrayM[position] floatValue] + margin;
}
CGFloat cellW = ;
CGFloat cellH = cellHeight;
cell.frame = CGRectMake(cellX, cellY, cellW, cellH);
// cell.backgroundColor = [UIColor redColor];
cell.backgroundColor = [UIColor colorWithRed:(arc4random() % ) / 250.0 green:(arc4random() % ) / 250.0 blue:(arc4random() % ) / 250.0 alpha:1.0]; // NSLog(@"%@", NSStringFromCGRect(cell.frame));
return cell;
} - (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
CGFloat cellW = ;
CGFloat cellH = + (arc4random() % );
[self.heightArrayM addObject:@(cellH)]; return CGSizeMake(cellW, cellH); }
@end
<2>下面介绍第二种(Swift实现)
效果图如下所示:
这种实现方法就是比较成熟的了,我把它封装成一个类.其实主要是实现三个函数
1)重写父类的prepare方法,准备所有cell的样式
extension WaterfallLayout {
// prepare准备所有Cell的布局样式
override func prepare() {
super.prepare()
// 0.获取item的个数
let itemCount = collectionView!.numberOfItems(inSection: )
// 1.获取列数
let cols = dataSource?.numberOfColsInWaterfallLayout?(self) ??
// 2.计算Item的宽度
let itemW = (collectionView!.bounds.width - self.sectionInset.left - self.sectionInset.right - self.minimumInteritemSpacing * CGFloat((cols - ))) / CGFloat(cols)
// 3.计算所有的item的属性
for i in startIndex..<itemCount {
// 1.设置每一个Item位置相关的属性
let indexPath = IndexPath(item: i, section: )
// 2.根据位置创建Attributes属性
let attrs = UICollectionViewLayoutAttributes(forCellWith: indexPath)
// 3.随机一个高度
guard let height = dataSource?.waterfallLayout(self, indexPath: indexPath) else {
fatalError("请设置数据源,并且实现对应的数据源方法")
}
// 4.取出最小列的位置
var minH = colHeights.min()!
let index = colHeights.index(of: minH)!
minH = minH + height + minimumLineSpacing
colHeights[index] = minH
// 5.设置item的属性
attrs.frame = CGRect(x: self.sectionInset.left + (self.minimumInteritemSpacing + itemW) * CGFloat(index), y: minH - height - self.minimumLineSpacing, width: itemW, height: height)
attrsArray.append(attrs)
}
// 4.记录最大值
maxH = colHeights.max()!
// 5.给startIndex重新复制
startIndex = itemCount
}
}
2)返回设置cell样式的数组
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
return attrsArray
}
3)返回当前的contentSize
override var collectionViewContentSize: CGSize {
return CGSize(width: , height: maxH + sectionInset.bottom - minimumLineSpacing)
}
总结:
在下面我封装的这个类中,只需要遵守我的数据代理源协议并且实现我的协议中的两个方法,传给我对应得高度(我这里是传的随机的),可选的方法,若是不实现,会有一个默认值,就可以实现该功能.协议如下:
@objc protocol WaterfallLayoutDataSource : class {
func waterfallLayout(_ layout : WaterfallLayout, indexPath : IndexPath) -> CGFloat
@objc optional func numberOfColsInWaterfallLayout(_ layout : WaterfallLayout) -> Int
}
完成代码如下所示:
ViewController.swift中的代码:
import UIKit
extension UIColor {
class func randomColor() -> UIColor {
return UIColor(colorLiteralRed: Float(arc4random_uniform()) / 255.0, green: Float(arc4random_uniform()) / 255.0, blue: Float(arc4random_uniform()) / 255.0, alpha: 1.0)
}
}
private let kWaterCellID = "kWaterCellID"
class ViewController: UIViewController {
var count : Int =
override func viewDidLoad() {
super.viewDidLoad()
// 1.设置布局
let layout = WaterfallLayout()
layout.minimumLineSpacing =
layout.minimumInteritemSpacing =
layout.sectionInset = UIEdgeInsets(top: , left: , bottom: , right: )
layout.dataSource = self
// 2.创建UICollectionView
let collectionView = UICollectionView(frame: view.bounds, collectionViewLayout: layout)
collectionView.dataSource = self
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: kWaterCellID)
view.addSubview(collectionView)
}
}
extension ViewController : UICollectionViewDataSource {
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return count
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: kWaterCellID, for: indexPath)
cell.backgroundColor = UIColor.randomColor()
if indexPath.item == count - {
count +=
collectionView.reloadData()
}
return cell
}
}
extension ViewController : WaterfallLayoutDataSource {
func waterfallLayout(_ layout: WaterfallLayout, indexPath: IndexPath) -> CGFloat {
return CGFloat(arc4random_uniform() + )
}
func numberOfColsInWaterfallLayout(_ layout: WaterfallLayout) -> Int {
return
}
}
封装自定义布局中的WaterfallLayout.swift代码如下:
import UIKit
@objc protocol WaterfallLayoutDataSource : class {
func waterfallLayout(_ layout : WaterfallLayout, indexPath : IndexPath) -> CGFloat
@objc optional func numberOfColsInWaterfallLayout(_ layout : WaterfallLayout) -> Int
}
class WaterfallLayout: UICollectionViewFlowLayout {
// MARK: 对外提供属性
weak var dataSource : WaterfallLayoutDataSource?
// MARK: 私有属性
fileprivate lazy var attrsArray : [UICollectionViewLayoutAttributes] = [UICollectionViewLayoutAttributes]()
fileprivate var totalHeight : CGFloat =
fileprivate lazy var colHeights : [CGFloat] = {
let cols = self.dataSource?.numberOfColsInWaterfallLayout?(self) ??
var colHeights = Array(repeating: self.sectionInset.top, count: cols)
return colHeights
}()
fileprivate var maxH : CGFloat =
fileprivate var startIndex =
}
extension WaterfallLayout {
// prepare准备所有Cell的布局样式
override func prepare() {
super.prepare()
// 0.获取item的个数
let itemCount = collectionView!.numberOfItems(inSection: )
// 1.获取列数
let cols = dataSource?.numberOfColsInWaterfallLayout?(self) ??
// 2.计算Item的宽度
let itemW = (collectionView!.bounds.width - self.sectionInset.left - self.sectionInset.right - self.minimumInteritemSpacing * CGFloat((cols - ))) / CGFloat(cols)
// 3.计算所有的item的属性
for i in startIndex..<itemCount {
// 1.设置每一个Item位置相关的属性
let indexPath = IndexPath(item: i, section: )
// 2.根据位置创建Attributes属性
let attrs = UICollectionViewLayoutAttributes(forCellWith: indexPath)
// 3.随机一个高度
guard let height = dataSource?.waterfallLayout(self, indexPath: indexPath) else {
fatalError("请设置数据源,并且实现对应的数据源方法")
}
// 4.取出最小列的位置
var minH = colHeights.min()!
let index = colHeights.index(of: minH)!
minH = minH + height + minimumLineSpacing
colHeights[index] = minH
// 5.设置item的属性
attrs.frame = CGRect(x: self.sectionInset.left + (self.minimumInteritemSpacing + itemW) * CGFloat(index), y: minH - height - self.minimumLineSpacing, width: itemW, height: height)
attrsArray.append(attrs)
}
// 4.记录最大值
maxH = colHeights.max()!
// 5.给startIndex重新复制
startIndex = itemCount
}
}
extension WaterfallLayout {
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
return attrsArray
}
override var collectionViewContentSize: CGSize {
return CGSize(width: , height: maxH + sectionInset.bottom - minimumLineSpacing)
}
}