CollectionView-自定义Item排布

之前写git商城的时候看到类似需求自定义的item排布，这两天有人又问到我具体怎么样自定义layout来实现，所以写了demo来分享下实现的过程。

类似APP实现截图

demo实现效果图

下面具体分析实现步骤

1.首先初始化懒加载一个CollectionView，注册Cell，Header，Footer~

#pragma mark - LazyLoad
- (UICollectionView *)collectionView
{
    if (!_collectionView) {
        DCItemSortLayout *dcLayout = [DCItemSortLayout new];
        dcLayout.delegate = self;
        
        _collectionView = [[UICollectionView alloc] initWithFrame:CGRectZero collectionViewLayout:dcLayout];
        _collectionView.frame = self.view.bounds;
        _collectionView.delegate = self;
        _collectionView.dataSource = self;

        _collectionView.alwaysBounceVertical = YES;
        [self.view addSubview:_collectionView];
        
        [self.collectionView registerClass:[DCCollectionItemCell class] forCellWithReuseIdentifier:DCCollectionItemCellID]; //注册cell
        
        [self.collectionView registerClass:[DCHeaderReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:DCHeaderReusableViewID]; //注册头部
        [self.collectionView registerClass:[DCFooterReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:DCFooterReusableViewID]; //注册尾部
    }
    return _collectionView;
}

2.自定义DCItemSortLayout 在.h写两个代理方法，返回每组section头部和尾部的高度

@protocol DCItemSortLayoutDelegate <NSObject>

@optional;

/* 头部高度 */
-(CGFloat)dc_HeightOfSectionHeaderForIndexPath:(NSIndexPath *)indexPath;
/* 尾部高度 */
-(CGFloat)dc_HeightOfSectionFooterForIndexPath:(NSIndexPath *)indexPath;

@end

@interface DCItemSortLayout : UICollectionViewFlowLayout


@property (nonatomic, assign) id<DCItemSortLayoutDelegate>delegate;

3.在DCItemSortLayout .m文件中调用prepareLayout方法，声明一个高度和可变字典

@property (nonatomic, assign) CGFloat overallHeight;     //整体高
@property (nonatomic, strong) NSMutableArray *attrsArr;  //布局数组

/**
 1.一个Cell对应一个UICollectionViewLayoutAttributes对象
 2.UICollectionViewLayoutAttributes对象决定了cell的摆设位置（frame）
 */
#pragma mark - 初始化属性（section/item）
- (void)setUpAttributes
{
    NSMutableArray *attributesArray = [NSMutableArray array];
    NSInteger sectionCount = [self.collectionView numberOfSections];
    for (int i = 0; i < sectionCount; i++) { //遍历
        //sectionHeader
        NSIndexPath *indexPath = [NSIndexPath indexPathWithIndex:i];
        UICollectionViewLayoutAttributes *attrheader = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
        [attributesArray addObject:attrheader];
    
        //sectionItem
        NSInteger itemCount = [self.collectionView numberOfItemsInSection:i];
        for (int j = 0; j < itemCount; j++) {
            NSIndexPath *indexPath = [NSIndexPath indexPathForItem:j inSection:i];
            UICollectionViewLayoutAttributes *attrs = [self layoutAttributesForItemAtIndexPath:indexPath];
            [attributesArray addObject:attrs];
        }
        //sectionfooter
        UICollectionViewLayoutAttributes *attrFooter = [self layoutAttributesForSupplementaryViewOfKind:UICollectionElementKindSectionFooter atIndexPath:indexPath];
        [attributesArray addObject:attrFooter];
    }
    
    self.attrsArr = [NSMutableArray arrayWithArray:attributesArray];
}

#pragma mark - 对应indexPath的位置的追加视图的布局属性
-(UICollectionViewLayoutAttributes *)layoutAttributesForSupplementaryViewOfKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath {
    
    UICollectionViewLayoutAttributes *layoutAttrbutes = [UICollectionViewLayoutAttributes layoutAttributesForSupplementaryViewOfKind:elementKind withIndexPath:indexPath];
    CGFloat height = 0;
    
    if (elementKind == UICollectionElementKindSectionHeader) { //头部
        if (_delegate != nil && [_delegate respondsToSelector:@selector(dc_HeightOfSectionHeaderForIndexPath:)]) {
            height = [_delegate dc_HeightOfSectionHeaderForIndexPath:indexPath];
        }
    } else { //尾部
        if (_delegate != nil && [_delegate respondsToSelector:@selector(dc_HeightOfSectionFooterForIndexPath:)]) {
            height = [_delegate dc_HeightOfSectionFooterForIndexPath:indexPath];
        }
    }
    layoutAttrbutes.frame = CGRectMake(0, self.overallHeight, ScreenW, height);
    
    self.overallHeight += height;
    
    return layoutAttrbutes;
}

#pragma mark - 返回rect中的所有的元素的布局属性
-(NSArray<UICollectionViewLayoutAttributes *> *)layoutAttributesForElementsInRect:(CGRect)rect{
    
    return self.attrsArr;
}

在我写的demo中我自定义了两组section

很明显的可以看出 上面这一组中有4个item，代码实现如下

#pragma mark - 自定义第一组section
- (void)layoutAttributesForCustomOneLayout:(UICollectionViewLayoutAttributes *)layoutAttributes indexPath: (NSIndexPath *) indexPath {
    
    CGFloat itemY = self.overallHeight;
    
    if (indexPath.item == 0) {
        CGFloat itemH = 80;
        layoutAttributes.frame = CGRectMake(0, itemY, ScreenW, itemH);
        
        self.overallHeight += itemH;
        
    } else {

        NSInteger row = (indexPath.item -1) % 3;
        CGFloat itemH = 100;
        CGFloat itemW = ScreenW / 3;
        
        layoutAttributes.frame = CGRectMake(row * itemW, itemY, itemW, itemH);
        
        if (indexPath.item == 3 || indexPath.item == [self.collectionView numberOfItemsInSection:indexPath.section] - 1) {
            
            self.overallHeight += itemH;
        }
    }
}

这一组中有3个item，代码实现如下

#pragma mark - 自定义第二组section
- (void)layoutAttributesForCustomTwolayout:(UICollectionViewLayoutAttributes *)layoutAttributes indexPath: (NSIndexPath *) indexPath {
    
    CGFloat itemY = self.overallHeight;
    CGFloat itemW = ScreenW / 2;
    CGFloat itemH = 160;
    
    switch (indexPath.item) {
        case 0:
            layoutAttributes.frame = CGRectMake(0, itemY, itemW, itemH);
            break;
        case 1:
            layoutAttributes.frame = CGRectMake(itemW, itemY, itemW, itemH/2);
            break;
        case 2:
            layoutAttributes.frame = CGRectMake(itemW, (itemH/2) + itemY, itemW, itemH / 2.0);
            break;
        default:
            break;
    }
    
    
    if (indexPath.item == [self.collectionView numberOfItemsInSection:indexPath.section] - 1) {
        self.overallHeight += itemH;
    }
}

这样我们在自定义的UICollectionViewFlowLayout中已经完成了对两组Items的布局，接下来我们来到控制器界面~

数据源UICollectionViewDataSource

#pragma mark - UICollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    
    return 2;
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
    
    return (section == 0) ? 4 : 3;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    
    if (indexPath.section == 0) {
        
        DCCollectionItemCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:DCCollectionItemCellID forIndexPath:indexPath];
        cell.backgroundColor = [self RandomColor];
        return cell;
    }else{
        
        DCCollectionItemCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:DCCollectionItemCellID forIndexPath:indexPath];
        cell.backgroundColor = [self RandomColor];
        return cell;
    }
    
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
    
    if (kind == UICollectionElementKindSectionHeader) {
        
        DCHeaderReusableView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:DCHeaderReusableViewID forIndexPath:indexPath];
        headerView.headLabel.text = [NSString stringWithFormat:@"第%zd组头部",indexPath.section];
        return headerView;
        
    } else if (kind == UICollectionElementKindSectionFooter) {
        
        DCFooterReusableView *footerView = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:DCFooterReusableViewID forIndexPath:indexPath];
        footerView.backgroundColor = [UIColor lightGrayColor];
        return footerView;
    }
    
    return [UICollectionReusableView new];
}

代理注意包括我们自定义的代理 DCItemSortLayoutDelegate,UICollectionViewDelegate

#pragma mark - UICollectionViewDelegate
#pragma mark - item点击
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
    
    NSLog(@"点击了第%zd组，第%zd个item",indexPath.section ,indexPath.row);
}

#pragma mark - DCItemSortLayoutDelegate
#pragma mark - 底部高度
-(CGFloat)dc_HeightOfSectionFooterForIndexPath:(NSIndexPath *)indexPath {
    return 20;
}
#pragma mark - 头部高度
-(CGFloat)dc_HeightOfSectionHeaderForIndexPath:(NSIndexPath *)indexPath {
    return 50;
}

• 这样自定义layout就完成了，之前也参考过几个git上几个哥们的布局对于自定义layout 的理解，很有收获非常感谢~
• 如上实现源码基本已全部展示，如果有需要我写的demo，可以给我留言私法~