超简单实现tableView下拉放大效果

头部下拉demo.gif

页面层级是先添加头部图片imageView，然后添加tableView，设置其tableHeaderView的frame与imageHeader一致，记录imageHeader的初始frame.

- (void)initSubViews
{
    self.imageHeader = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.width * 3 / 4)];
    self.imageHeader.image = [UIImage imageNamed:@"image"];
    frameF = self.imageHeader.frame;
    [self.view addSubview:self.imageHeader];
    
    [self.view addSubview:self.tableView];
    
    UIView *headerView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.width * 3/ 4)];
    headerView.backgroundColor = [UIColor clearColor];
    self.tableView.tableHeaderView = headerView;
}

懒加载tableView

- (UITableView *)tableView
{
    if (!_tableView) {
        _tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, self.view. bounds.size.width, self.view.bounds.size.height)];
        _tableView.dataSource = self;
        _tableView.delegate = self;
        _tableView.backgroundColor = [UIColor clearColor];
    }
    return _tableView;
}

重点在于UIScrollView的代理方法

#pragma mark - UIScrollView Delegate
-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    //frameF为最初image的位置
    CGFloat offset = scrollView.contentOffset.y;
    if (offset > 0) {
        CGRect frame = frameF;
        frame.origin.y = frameF.origin.y - offset;
        self.imageHeader.frame = frame;
    }else{
        CGRect frame = frameF;
        frame.size.height = frameF.size.height - offset;
        frame.size.width = frame.size.height * 4 / 3;
        frame.origin.x = frameF.origin.x - (frame.size.width - frameF.size.width) / 2;
        self.imageHeader.frame = frame;
    }
}

一切搞定。