iOS瀑布流实现(Swift)

Posted 2020-08-21 木子沉雨

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 = 100;
    CGFloat cellH = 100 + (arc4random() % 80);
    [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 * 100 + (num2 + 1) * margin;
    CGFloat cellY = 0;
    for (int i = 0; i < num1; i++) {
        NSInteger position =  num2 + i * 3;
        cellY += [self.heightArrayM[position] floatValue] + margin;
    }
    CGFloat cellW = 100;
    CGFloat cellH = cellHeight;
    cell.frame = CGRectMake(cellX, cellY, cellW, cellH);
//    cell.backgroundColor = [UIColor redColor];
    cell.backgroundColor = [UIColor colorWithRed:(arc4random() % 250) / 250.0 green:(arc4random() % 250) / 250.0 blue:(arc4random() % 250) / 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 60;
}

- (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 * 100 + (num2 + 1) * margin;
    CGFloat cellY = 0;
    for (int i = 0; i < num1; i++) {
        NSInteger position =  num2 + i * 3;
        cellY += [self.heightArrayM[position] floatValue] + margin;
    }
    CGFloat cellW = 100;
    CGFloat cellH = cellHeight;
    cell.frame = CGRectMake(cellX, cellY, cellW, cellH);
//    cell.backgroundColor = [UIColor redColor];
    cell.backgroundColor = [UIColor colorWithRed:(arc4random() % 250) / 250.0 green:(arc4random() % 250) / 250.0 blue:(arc4random() % 250) / 250.0 alpha:1.0];
    
//    NSLog(@"%@", NSStringFromCGRect(cell.frame)); 
    return cell;
}

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
    CGFloat cellW = 100;
    CGFloat cellH = 100 + (arc4random() % 80);
    [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: 0)
        
        // 1.获取列数
        let cols = dataSource?.numberOfColsInWaterfallLayout?(self) ?? 2
        
        // 2.计算Item的宽度
        let itemW = (collectionView!.bounds.width - self.sectionInset.left - self.sectionInset.right - self.minimumInteritemSpacing * CGFloat((cols - 1))) / 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: 0)
            
            // 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: 0, 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(256)) / 255.0, green: Float(arc4random_uniform(256)) / 255.0, blue: Float(arc4random_uniform(256)) / 255.0, alpha: 1.0)
    }
}

private let kWaterCellID = "kWaterCellID"

class ViewController: UIViewController {
    
    var count : Int = 20
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 1.设置布局
        let layout = WaterfallLayout()
        layout.minimumLineSpacing = 10
        layout.minimumInteritemSpacing = 10
        layout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
        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 - 1 {
            count += 20
            
            collectionView.reloadData()
        }
        
        return cell
    }
}


extension ViewController : WaterfallLayoutDataSource {
    func waterfallLayout(_ layout: WaterfallLayout, indexPath: IndexPath) -> CGFloat {
        return CGFloat(arc4random_uniform(80) + 100)
    }
    
    func numberOfColsInWaterfallLayout(_ layout: WaterfallLayout) -> Int {
        return 3
    }
}

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 = 0
    fileprivate lazy var colHeights : [CGFloat] = {
        let cols = self.dataSource?.numberOfColsInWaterfallLayout?(self) ?? 2
        var colHeights = Array(repeating: self.sectionInset.top, count: cols)
        return colHeights
    }()
    fileprivate var maxH : CGFloat = 0
    fileprivate var startIndex = 0
}


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: 0)
        
        // 1.获取列数
        let cols = dataSource?.numberOfColsInWaterfallLayout?(self) ?? 2
        
        // 2.计算Item的宽度
        let itemW = (collectionView!.bounds.width - self.sectionInset.left - self.sectionInset.right - self.minimumInteritemSpacing * CGFloat((cols - 1))) / 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: 0)
            
            // 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: 0, height: maxH + sectionInset.bottom - minimumLineSpacing)
    }
}