scrollView中内部控件的悬停

以下图为例，图片，红色view和蓝色view是添加在scrollView上的，向上拖动，红色view停留在屏幕顶端不动，其它的继续滚动，向下拖动后，红色view跟着下来

代码如下:(注意的是scrollView中自动布局的设置问题)

 1 #import "ViewController.h"

 2 @interface ViewController () <UIScrollViewDelegate>

 3 @property (weak, nonatomic) IBOutlet UIScrollView *scrollView;

 4 @property (weak, nonatomic) IBOutlet UIView *blueView;

 5 @property (weak, nonatomic) IBOutlet UIView *redView;

 6 @property (weak, nonatomic) IBOutlet UIImageView *imageView;

 7 @end

 8 @implementation ViewController

 9 - (void)viewDidLoad {

10     [super viewDidLoad];

11     self.scrollView.contentSize = CGSizeMake(0, CGRectGetMaxY(self.blueView.frame));

12 }

13

14 - (void)scrollViewDidScroll:(UIScrollView *)scrollView

15 {

16     CGFloat imageH = self.imageView.frame.size.height;

17     CGFloat offsetY = scrollView.contentOffset.y;

18     if (offsetY >= imageH) {

19         //将红色控件添加到控制器View中

20         CGRect redFrame = self.redView.frame;

21         redFrame.origin.y = 0;

22         self.redView.frame = redFrame;

23         [self.view addSubview:self.redView];

24     }else {

25         //将红色控件添加到控制器scrollView中

26         CGRect redFrame = self.redView.frame;

27         redFrame.origin.y = 140;

28         self.redView.frame = redFrame;

29         [self.scrollView addSubview:self.redView];

30     }

31

32 //    if (offsetY < 0) {

33 //        CGFloat scale = 1 - (offsetY / 80);

34 //        self.imageView.transform = CGAffineTransformMakeScale(scale, scale);

35 //    }

36

37     CGFloat scale = 1 - (offsetY / 20);

38     scale = (scale >= 1) ? scale : 1;

39     self.imageView.transform = CGAffineTransformMakeScale(scale, scale);

40 }

41 @end