iOS：如何同步两个 UIScrollview

Question

我有两个水平UIScrollviews。当用户在其中任何一个中拖动手指时，我想同步它们的滚动。这是我的代码：

self.topScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
self.topScrollView.delegate = self;
self.topScrollView.bounces = YES;

self.bottomScrollView = [[UIScrollView alloc] initWithFrame:CGRectZero];
self.bottomScrollView.delegate = self;
self.bottomScrollView.bounces = YES;
...

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    if (scrollView == self.topScrollView)
    {
        self.bottomScrollView.delegate = nil;
    }
    else
    {
        self.topScrollView.delegate = nil;
    }
    ...
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{   
    ...
    self.topScrollView.delegate = self;
    self.bottomScrollView.delegate = self;
}

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    ...
    self.topScrollView.delegate = self;
    self.bottomScrollView.delegate = self;
}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    // Sync the two scroll views
    if (scrollView == self.topScrollView)
    {
        [self.bottomScrollView setContentOffset:scrollView.contentOffset animated:NO];
    }
    else
    {
        [self.topScrollView setContentOffset:scrollView.contentOffset animated:NO];
    }
    ...
}

两个滚动视图确实同步滚动，但是，问题是所有的弹跳和减速都消失了。整个滚动运动变得非常僵硬。如果我删除所有同步代码，那么每个滚动视图都可以单独正常工作。那么，问题是什么？还是UIScrollView不能同步？

Answer 1

您可以使用topScrollView.panGestureRecognizer和bottomScrollView.panGestureRecognizer来获取两个手势识别器，并将它们添加到包含两个滚动视图的公共超级视图中。然后，两个孩子都会识别出该超级视图上的平移手势。

您很可能还需要成为两个识别器的代表，并让它们同时被识别：

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}