- (void)viewDidLoad {    [super viewDidLoad];        UIScrollView *scrollView = [[UIScrollView alloc] init];    scrollView.frame = self.view.bounds;    scrollView.delegate = self;    [scrollView addSubview:[[UISwitch alloc] init]];    scrollView.contentSize = CGSizeMake(self.view.frame.size.width, 1500);    scrollView.backgroundColor = [UIColor redColor];    [self.view addSubview:scrollView];        UIView *bar = [[UIView alloc] init];    bar.frame = CGRectMake(0, 70, self.view.frame.size.width, 50);    bar.backgroundColor = [[UIColor blueColor] colorWithAlphaComponent:0.5];    [scrollView addSubview:bar];    self.bar = bar;}#pragma mark - 
     
      - (void)scrollViewDidScroll:(UIScrollView *)scrollView{    if (scrollView.contentOffset.y >= 70) {//        self.bar.frame = CGRectMake(0, 0, self.view.frame.size.width, 50);//        [self.view addSubview:self.bar];        self.bar.frame = CGRectMake(0, scrollView.contentOffset.y, self.view.frame.size.width, 50);    } else {//        self.bar.frame = CGRectMake(0, 70, self.view.frame.size.width, 50);//        [scrollView addSubview:self.bar];    }}