一个iOS 列表头部放大工具

头部放大是移动端开发常用到的UI，这里封装了一个便于使用的头部方放大工具，UITableView 和 UICollectionView 都可以使用

实现代码

+ (VVScrollViewHelper *)initWithScrollView:(UIScrollView *)scrollView
                          headerViewConfig:(VVScrollExtraViewConfig *)headerConfig
{
    VVScrollViewHelper *scrollViewHelper = [[self alloc] init];
    if(scrollViewHelper){
        
        headerConfig.frontView.clipsToBounds = YES;
        headerConfig.backgroundView.clipsToBounds = YES;
        scrollViewHelper.extraHeaderViewConfig = headerConfig;
        
        CGRect frame = headerConfig.frontView.frame;
        CGPoint origin = frame.origin;
        ///y原点 = 背景视图的原高度 - inset高度
        origin.y = - (CGRectGetHeight(frame) - headerConfig.headerOverHeight);
        frame.origin = origin;
        headerConfig.frontView.frame = frame;
        headerConfig.backgroundView.frame = frame;
        scrollViewHelper.scrollView = scrollView;
        
        scrollViewHelper.contentInsetTop = CGRectGetHeight(frame) - headerConfig.headerOverHeight;
        scrollViewHelper.contentInsetBottom = 0;
        scrollView.contentInset = UIEdgeInsetsMake(scrollViewHelper.contentInsetTop, 0, scrollViewHelper.contentInsetBottom, 0);
        [scrollView setContentOffset:CGPointMake(0, -scrollViewHelper.contentInsetTop) animated:NO];
        scrollView.bouncesZoom = NO;
        [scrollView addSubview:headerConfig.backgroundView];
        [scrollView addSubview:headerConfig.frontView];
        scrollViewHelper.frontViewFrame = headerConfig.frontView.frame;
    }
    return scrollViewHelper;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    if (self.extraHeaderViewConfig) {
        CGRect frame = self.extraHeaderViewConfig.frontView.frame;
        CGPoint origin = frame.origin;
        CGSize size = frame.size;
        ///下拉,
        BOOL downPull = !(scrollView.contentOffset.y > - (CGRectGetHeight(frame) - self.extraHeaderViewConfig.headerOverHeight));
        ///放大
        BOOL expand = self.extraHeaderViewConfig.headerStyle == VVHeaderBackStyleExpand;
        if (downPull && expand) {
            ///初始偏移量为 (-self.contentInsetTop
            origin.y = scrollView.contentOffset.y;
            size.height = - scrollView.contentOffset.y + self.extraHeaderViewConfig.headerOverHeight;
            frame.origin = origin;
            frame.size = size;
            self.extraHeaderViewConfig.backgroundView.frame = frame;
        }
    }

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW,
                                 (int64_t)(0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        ///将背景视图插到最底层
        [scrollView insertSubview:self.extraHeaderViewConfig.backgroundView
                              atIndex:0];
        ///将顶部内容视图插到第二底层,防止覆盖cell,导致cell不能点击
        [scrollView insertSubview:self.extraHeaderViewConfig.frontView atIndex:1];
    });
}

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效果图

使用方法

- (VVScrollViewHelper *)headerHelper
{
    if (!_headerHelper) {
        VVScrollExtraViewConfig  *config = [[VVScrollExtraViewConfig alloc] init];
        config.backgroundView = self.imgView;
        config.frontView = self.headerContentView;
        config.headerOverHeight = 40;
        _headerHelper = [VVScrollViewHelper initWithScrollView:self.tableView headerViewConfig:config];
    }
    return _headerHelper;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    [self.headerHelper scrollViewDidScroll:scrollView];
}

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demo
如果对你有帮助，欢迎star