iOS瀑布流实现(Swift)

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)
    }
}