tableView 头视图下拉放大 重写

#import "TableViewController.h"

@interface TableViewController ()
@property (nonatomic, retain) UIImageView *headerImageView;
@end

@implementation TableViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self layoutHeaderImageView];
}

- (void)layoutHeaderImageView {
    UIView *headerView = [[UIView alloc] initWithFrame:(CGRectMake(0, 0, self.view.frame.size.width, 200))];
    self.headerImageView = [[UIImageView alloc] initWithFrame:(CGRectMake(0, 0, self.view.frame.size.width, 200))];
    self.headerImageView.image  = [UIImage imageNamed:@"pic5093_sc115.com.jpg"]; // 自己选择的图片
    [headerView addSubview:self.headerImageView];
    self.tableView.tableHeaderView = headerView;
    
}

// 下拉后图片拉伸的效果方法下载这个里面
- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    CGFloat width = self.view.frame.size.width; // 图片宽度
    CGFloat yOffset = scrollView.contentOffset.y;  // 偏移的y值
    if (yOffset < 0) {
        CGFloat totalOffset = 200 + ABS(yOffset);
        CGFloat f = totalOffset / 200;
        self.headerImageView.frame =  CGRectMake(- (width * f - width) / 2, yOffset, width * f, totalOffset); //拉伸后的图片的frame应该是同比例缩放。
    }
}

这个方法是有效的，我自己在刚才又重新写了一遍