ios - 基于 ScrollView Position 的 UIImageView Fading

Question

我有一个 UIPageControl 可以翻阅不同的页面。当用户从第 1 页滚动到第 2 页时，我想让 UIImageView 开始淡出。我正在努力找出根据位置添加图层的正确方法。任何帮助将不胜感激...

[UIView beginAnimations:@"fade out" context:nil];
    [UIView setAnimationDuration:1.0]; // some how based on position?? 
    imageView.alpha = 1.0; // here to?
    [UIView commitAnimations];

编辑:

设置委托(delegate):

 self.pageController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];

    self.pageController.dataSource = self;

Answer 1

您需要委托(delegate)重写以下方法:

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;

然后您应该检查 scrollView.contentOffset.x 值以确定 ScrollView 水平滚动了多少，并使用它来确定您的 imageView 的 alpha，如下所示:

CGFloat newAlpha = scrollView.contentOffset.x / scrollView.frame.size.width; // This will need to be adapted depending on the content size of your scroll view -- do not just copy and paste this expecting it to work :)
imageView.alpha = newAlpha;