UITableView拉伸效果

1. 创建一个UITableView 和一个UIImageView
   

   @property (nonatomic, strong) UITableView *tableView;

   @property (nonatomic, strong) UIImageView *headerImgaeView;

2. 初始化

   - (void)viewDidLoad {
       [super viewDidLoad];
   
       self.tableView = [[UITableView alloc] initWithFrame:CGRectMake(0, 0, 320, 568) style:UITableViewStyleGrouped];
       self.tableView.delegate = self;
       self.tableView.dataSource = self;
       [self.view addSubview:self.tableView];
       
       
       [self layoutHeaderImageView];
   }

    

3. layoutHeaderImageView

   - (void)layoutHeaderImageView
   {
       UIView *headerBackView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 150)];
       headerBackView.backgroundColor = [UIColor lightGrayColor];
       self.tableView.tableHeaderView = headerBackView;
       
       self.headerImgaeView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 150)];
       self.headerImgaeView.backgroundColor = [UIColor greenColor];
       self.headerImgaeView.image = [UIImage imageNamed:@"beautiful.jpg"];
       self.headerImgaeView.contentMode = UIViewContentModeScaleAspectFill;
       self.headerImgaeView.clipsToBounds = YES;
       [headerBackView addSubview:self.headerImgaeView];
   
   }

4. 滚动偏移的主要方法（这个为UIScrollViewDelegate中的代理方法）
   
   

   - (void)scrollViewDidScroll:(UIScrollView *)scrollView
   {
       CGFloat width = self.view.frame.size.width;// 图片宽度
       CGFloat yOffset = scrollView.contentOffset.y; //偏移量
       
       NSLog(@":  %.2f", yOffset);
       
       if (yOffset < 0) {
           CGFloat totalOffset = 150 + ABS(yOffset);
           CGFloat f = totalOffset / 150; //缩放系数
           
           self.headerImgaeView.frame = CGRectMake(-(width * f - width) / 2, yOffset, width * f, totalOffset); //拉伸后的frame是同比例缩放
       }
       
       if (yOffset > 0) {
           CGFloat totalOffset = 150 - ABS(yOffset);
           CGFloat f = totalOffset / 150;
           
           self.headerImgaeView.frame = CGRectMake(-(width * f - width) / 2, yOffset, width * f, totalOffset);
       }
   }