问题描述
我有一个基于 Apple 的 PageControl 示例的应用程序.第一次加载视图时,滚动视图会加载第 0 页和第 1 页.每当启动滚动时,UIKit 应该调用 scrollViewDidScroll 方法对吗?
I have an app based on Apple's PageControl sample. The first time the view loads, the scroll view is loaded with page 0 and page 1. Whenever a scroll is initiated, the scrollViewDidScroll method should get called by UIKit correct?
从第 0 页开始滚动到第 1 页时,应用应加载第 1 页、第 1 页和第 1 页,(以防止滚动时闪烁).
When initiating a scroll from page 0 to page 1, the app should load page-1, page and page+1, (to prevent flashes during scrolling).
我的应用程序似乎调用了 scrollViewDidScroll 19 次,而我的 loadScrollViewWithPage: 方法在页面 0 和页面 1 中调用了 19 次,最终到达页面 1 和页面 2,然后它崩溃了.
My app seems to call scrollViewDidScroll 19 times and my loadScrollViewWithPage: method 19 times each with page 0 and page 1, before it finally gets to page 1 and 2, then it crashes.
这些是方法:
- (void)scrollViewDidScroll:(UIScrollView *)sender { NSLog(@"scrollviewdidscroll"); // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in // which a scroll event generated from the user hitting the page control triggers updates from // the delegate method. We use a boolean to disable the delegate logic when the page control is used. if (pageControlUsed) { // do nothing - the scroll was initiated from the page control, not the user dragging return; } // Switch the indicator when more than 50% of the previous/next page is visible CGFloat pageWidth = scrollView.frame.size.width; int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1; pageControl.currentPage = page; // load the visible page and the page on either side of it (to avoid flashes when the user starts scrolling) [self loadScrollViewWithPage:page - 1]; [self loadScrollViewWithPage:page]; [self loadScrollViewWithPage:page + 1]; // A possible optimization would be to unload the views+controllers which are no longer visible } - (void)loadScrollViewWithPage:(int)page { if (page < 0) return; if (page >= kNumberOfPages) return; NSLog(@"page: %i", page); // replace the placeholder if necessary KeyboardViewController *controller = [viewControllers objectAtIndex:page]; if ((NSNull *)controller == [NSNull null]) { controller = [[KeyboardViewController alloc] initWithPageNumber:page]; [viewControllers replaceObjectAtIndex:page withObject:controller]; [controller release]; } // add the controller's view to the scroll view CGRect frame = scrollView.frame; frame.origin.x = frame.size.width * page; frame.origin.y = 0; frame.size.height = scrollView.frame.size.height; controller.view.frame = frame; [scrollView setAutoresizesSubviews:YES]; [scrollView setAutoresizingMask:UIViewAutoresizingFlexibleWidth|UIViewAutoresizingFlexibleHeight]; [scrollView addSubview:controller.view]; }
为什么 scrollViewDidScroll 会被调用这么多次?
Why would scrollViewDidScroll get called so many times?
谢谢
推荐答案
scrollViewDidScroll: 每次滚动边界改变时都会被调用.这意味着它在滚动期间以及开始时被调用.您可能想尝试 scrollViewWillBeginDragging:.
scrollViewDidScroll: gets called every time the scroll bounds change. This means it gets called during the scroll, as well as when it starts. You may want to try scrollViewWillBeginDragging: instead.