使用setContentOffset:animated:
UIScrollView *scrollView = ...;
CGPoint newOffset = scrollView.contentOffset;
newOffset.y = 0;
[scrollView setContentOffset:newOffset animated:YES];
如果你想要开场动画的效果,在scrollView的viewcontroller实现
- (void)viewDidLoad
{
[super viewDidLoad];
// ...
CGPoint bottomOffset = CGPointMake(self.scrollView.contentOffset.x, self.scrollView.contentSize.height - self.scrollView.bounds.size.height);
[self.scrollView setContentOffset:bottomOffset animated:NO];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
CGPoint newOffset = self.scrollView.contentOffset;
newOffset.y = 0;
[self.scrollView setContentOffset:newOffset animated:YES];
}
补充:
移动的慢点,用timer实现:
- (void)viewDidLoad
{
[super viewDidLoad];
// ...
CGPoint bottomOffset = CGPointMake(self.scrollView.contentOffset.x, self.scrollView.contentSize.height - self.scrollView.bounds.size.height);
[self.scrollView setContentOffset:bottomOffset animated:NO];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
CGPoint bottomOffset = CGPointMake(self.scrollView.contentOffset.x, self.scrollView.contentSize.height - self.scrollView.bounds.size.height);
//设置延迟时间
float scrollDurationInSeconds = 4.0;
//计算timer间隔
float totalScrollAmount = bottomOffset.y;
float timerInterval = scrollDurationInSeconds / totalScrollAmount;
[NSTimer scheduledTimerWithTimeInterval:timerInterval target:self selector:@selector(scrollScrollView:) userInfo:nil repeats:YES];
}
- (void)scrollScrollView:(NSTimer *)timer
{
CGPoint newScrollViewContentOffset = self.scrollView.contentOffset;
//向上移动 1px
newScrollViewContentOffset.y -= 1;
newScrollViewContentOffset.y = MAX(0, newScrollViewContentOffset.y);
//如果到顶了,timer中止
if (newScrollViewContentOffset.y == 0) {
[timer invalidate];
}
//最后设置scollView's contentOffset
self.scrollView.contentOffset = newScrollViewContentOffset;
}