加载动态滚动条

_button2 = [UIButton buttonWithType:UIButtonTypeCustom];
_button2.backgroundColor = RGBCOLOR(50, 57, 66);
_button2.frame = CGRectMake(0, 64, self.view.width, 4);

_button = [UIButton buttonWithType:UIButtonTypeCustom];
_button.backgroundColor = [[UIColor whiteColor] colorWithAlphaComponent:0.4];
_button.frame = CGRectMake(self.view.width/2, 64, 0, 4);
[UIView animateWithDuration:1.0 delay:0 options:UIViewAnimationOptionRepeat | UIViewAnimationOptionAutoreverse animations:^{
_button.frame = CGRectMake(0, 64, self.view.width, 4);
} completion:nil];

[self.view addSubview:_button2];
[self.view addSubview:_button];