UIRefreshControl加到UIScrollView上下拉刷新，出现跳跃

- (void)viewDidLoad

UIScrollView

UIRefreshControl

viewDidLoad

 - (void)viewDidLoad

      {

       [super viewDidLoad];

       UIScrollView *scrollView = [[UIScrollView alloc]initWithFrame:CGRectMake(0, 0, [UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];

    [scrollView setBackgroundColor:[UIColor whiteColor]];

    [scrollView setContentSize:CGSizeMake([UIScreen mainScreen].bounds.size.width, [UIScreen mainScreen].bounds.size.height)];

    scrollView.alwaysBounceVertical = YES;

    [self.view addSubview:scrollView];

    UIView *topView = [[UIView alloc] initWithFrame:CGRectMake(0, -200, scrollView.bounds.size.width, 200)];

    [topView setBackgroundColor:[UIColor brownColor]];

    [scrollView addSubview:topView];

    UIRefreshControl *refreshCOntrol= [[UIRefreshControl alloc] init];

    [refreshControl addTarget:self action:@selector(testRefresh:) forControlEvents:UIControlEventValueChanged];



    [scrollView addSubview:refreshControl];

    [self.view addSubview:scrollView];

    }