仿 Nice 首页图片列表 9 图样式 (iOS)

说明

本文的代码已经上传到 GitHub 上,有兴趣的童鞋可以到 GitHub 上查看,欢迎沟通交流。

https://github.com/light-bo/BLLSudokuImageLayout

需要实现的效果

用过 nice app 的童鞋应该比较熟悉,nice 对于图片贴的显示是根据图片数量有 9 种不同的显示样式的,如下图所示:

1 张图的样式
2 张图的样式
3 张图的样式
4 张图的样式
5 张图的样式
6 张图的样式
7 张图的样式
8 张图的样式
9 张图的样式

如何实现

看到上面这种显示效果,很多人应该很容易就能想到,可以使用 UICollecitonView 来实现,不过这布局仅仅使用 UIKit 提供的 UICollectionViewFlowLayout 还是有点难以实现,看来只能借助于 UICollectionViewFlowLayout 来自定义布局了,本文采用的实现方案就是自定义一个 UICollectionViewLayout 类(继承于 UICollectionViewFlowLayout),来达成效果。

看看代码

自定义 layout 类

//BLLCollectionViewImageSudokuLayout.h

//继承自 UICollectionViewFlowLayout
@interface BLLCollectionViewImageSudokuLayout : UICollectionViewFlowLayout

/**
 The intermal of each column.
 
 每一列的间距
 */
@property (nonatomic, assign) float columnMargin;

/**
 The interval of each row.
 
 每一行的间距
 */
@property (nonatomic, assign) float rowMargin;

@end

自定义布局中根据图片的数量,计算图片布局,这里使用策略模式,每一种布局由一个类负责。

@implementation BLLCollectionViewImageSudokuLayout

- (instancetype)init {
    self = [super init];
    if (self) {
        _attrsArray = [NSMutableArray new];
    }
    
    return self;
}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
    return YES;
}

- (void)prepareLayout {
    [super prepareLayout];
    
    //计算所有 cell 的属性
    [self.attrsArray removeAllObjects];
    NSInteger count = [self.collectionView numberOfItemsInSection:0];
    for (int i = 0; i<count; i++) {
        UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:[NSIndexPath indexPathForItem:i inSection:0]];
        [self.attrsArray addObject:attrs];
    }
}

- (CGSize)collectionViewContentSize {
    return CGSizeMake(self.collectionView.width, self.collectionView.height);
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect )rect {
    return self.attrsArray;
}

// 根据图片的数量,计算图片布局,这里使用策略模式,每一种布局由一个类负责,分别是 BLLSudokuItemLayoutAttributeAlgorithm1, BLLSudokuItemLayoutAttributeAlgorithm2, ...
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
    NSInteger itemAmount = [self.collectionView numberOfItemsInSection:0];
    
    Class algorithmClass =  NSClassFromString([NSString stringWithFormat:@"BLLSudokuItemLayoutAttributeAlgorithm%zd", itemAmount]);
    BLLSudokuItemLayoutConfigurator *layoutConfigurator = [[BLLSudokuItemLayoutConfigurator alloc] initWithAlgorithmStrategy:[algorithmClass new]];
    
    return [layoutConfigurator layoutConfigWithCollectionView:self indexPath:indexPath];
}

@end

布局算法协议


@protocol BLLSudokuItemLayoutAttributeAlgorithmProtocol <NSObject>

@required
- (UICollectionViewLayoutAttributes *)layoutConfigWithCollectionView:(BLLCollectionViewImageSudokuLayout *)collectionViewSudokuLayout indexPath:(NSIndexPath *)indexPath;

@end

布局算法基类


//BLLSudokuItemLayoutAttributeAlgorithm
@interface BLLSudokuItemLayoutAttributeAlgorithm : NSObject <BLLSudokuItemLayoutAttributeAlgorithmProtocol>

@end

具体算法子类

简单地列出图片数量为 4 时,算法子类的实现

//BLLSudokuItemLayoutAttributeAlgorithm4
@interface BLLSudokuItemLayoutAttributeAlgorithm4 : BLLSudokuItemLayoutAttributeAlgorithm

@end

@implementation BLLSudokuItemLayoutAttributeAlgorithm4

- (UICollectionViewLayoutAttributes *)layoutConfigWithCollectionView:(BLLCollectionViewImageSudokuLayout *)collectionViewSudokuLayout indexPath:(NSIndexPath *)indexPath {
    float width = collectionViewSudokuLayout.collectionView.width - collectionViewSudokuLayout.sectionInset.left - collectionViewSudokuLayout.sectionInset.right;
    float halfWidth = (width - collectionViewSudokuLayout.columnMargin)/2;
    float height = collectionViewSudokuLayout.collectionView.height - collectionViewSudokuLayout.sectionInset.top - collectionViewSudokuLayout.sectionInset.bottom;
    float halfHeight = (height - collectionViewSudokuLayout.rowMargin) / 2;
    
    UICollectionViewLayoutAttributes *attrs = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
    attrs.frame = CGRectMake((indexPath.row % 2) * (halfWidth + collectionViewSudokuLayout.columnMargin), (indexPath.row > 1? 1: 0) * (halfHeight+collectionViewSudokuLayout.rowMargin), halfWidth, halfHeight);
    
    return attrs;
}

@end

最后,类似于常规的 UICollectionViewLayout 的使用即可

   BLLCollectionViewImageSudokuLayout *collectionViewImageSudokuLayout = [[BLLCollectionViewImageSudokuLayout alloc] init];
    collectionViewImageSudokuLayout.columnMargin = 2;
    collectionViewImageSudokuLayout.rowMargin = 2;
    
    //yourWidth:整个图片区域的宽度  yourHeight:整个图片区域的高度
    _mainCollectionView = [[UICollectionView alloc] initWithFrame:CGRectMake(0, 0, yourWidth, yourHeight) collectionViewLayout:collectionViewImageSudokuLayout];
    _mainCollectionView.backgroundColor = [UIColor whiteColor];
    _mainCollectionView.delegate = self;
    _mainCollectionView.dataSource = self;
    [_mainCollectionView registerClass:[BLLImageCollectionViewCell class] forCellWithReuseIdentifier:kImageCellId];
    
    [self addSubview:_mainCollectionView];

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