在UIPageViewController中禁用跳动效果

到目前为止，没有任何答案可以完全有效。他们都失败的边缘情况是：

1. 滚动到第2页。
2. 用一根手指向页面1拖动。
3. 将第二只手指放在屏幕上，然后向页面1拖动。
4. 抬起第一根手指。
5. 重复直到您拖过第0页。

在这种情况下，到目前为止，我所见过的每个解决方案都超出了页面0的范围。核心问题是底层API被破坏了，并开始报告相对于页面0的内容偏移，而没有调用我们的回调让我们知道它显示了另一个页面。在整个过程中，API仍然声称显示第1页，而实际上是显示在第0页上，而实际上是在第0页，而在第-1页上。

此设计缺陷的解决方法非常丑陋，但是这里是：

@property (weak,nonatomic) UIPageControl *pageControl;
@property (nonatomic,assign) BOOL shouldBounce;
@property (nonatomic,assign) CGFloat lastPosition;
@property (nonatomic,assign) NSUInteger currentIndex;
@property (nonatomic,assign) NSUInteger nextIndex;

- (void)viewDidLoad {

    [super viewDidLoad];

...

    self.shouldBounce = NO;

    for (id testView in self.pageController.view.subviews) {
        UIScrollView *scrollView = (UIScrollView *)testView;
        if ([scrollView isKindOfClass:[UIScrollView class]]) {
            scrollView.delegate = self;
            // scrollView.bounces = self.shouldBounce;
        }
    }
}

- (NSInteger)presentationIndexForPageViewController:(UIPageViewController *)pageViewController{

    return (NSInteger)self.currentIndex;
}

- (void)pageViewController:(UIPageViewController *)pageViewController willTransitionToViewControllers:(NSArray *)pendingViewControllers{

    id controller = [pendingViewControllers firstObject];
    self.nextIndex = [viewControllers indexOfObject:controller];
}

- (void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed{

    if(completed) {
        // At this point, we can safely query the API to ensure
        // that we are fully in sync, just in case.
        self.currentIndex = [viewControllers indexOfObject:[pageViewController.viewControllers objectAtIndex:0]];
        [self.pageControl setCurrentPage:self.currentIndex];
    }

    self.nextIndex = self.currentIndex;

}

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    /* The iOS page view controller API is broken.  It lies to us and tells us
       that the currently presented view hasn't changed, but under the hood, it
       starts giving the contentOffset relative to the next view.  The only
       way to detect this brain damage is to notice that the content offset is
       discontinuous, and pretend that the page changed.
     */
    if (self.nextIndex > self.currentIndex) {
        /* Scrolling forwards */

        if (scrollView.contentOffset.x < (self.lastPosition - (.9 * scrollView.bounds.size.width))) {
            self.currentIndex = self.nextIndex;
            [self.pageControl setCurrentPage:self.currentIndex];
        }
    } else {
        /* Scrolling backwards */

        if (scrollView.contentOffset.x > (self.lastPosition + (.9 * scrollView.bounds.size.width))) {
            self.currentIndex = self.nextIndex;
            [self.pageControl setCurrentPage:self.currentIndex];
        }
    }

    /* Need to calculate max/min offset for *every* page, not just the first and last. */
    CGFloat minXOffset = scrollView.bounds.size.width - (self.currentIndex * scrollView.bounds.size.width);
    CGFloat maxXOffset = (([viewControllers count] - self.currentIndex) * scrollView.bounds.size.width);

    NSLog(@"Page: %ld NextPage: %ld X: %lf MinOffset: %lf MaxOffset: %lf\n", (long)self.currentIndex, (long)self.nextIndex,
          (double)scrollView.contentOffset.x,
          (double)minXOffset, (double)maxXOffset);

    if (!self.shouldBounce) {
        CGRect scrollBounds = scrollView.bounds;
        if (scrollView.contentOffset.x <= minXOffset) {
            scrollView.contentOffset = CGPointMake(minXOffset, 0);
            // scrollBounds.origin = CGPointMake(minXOffset, 0);
        } else if (scrollView.contentOffset.x >= maxXOffset) {
            scrollView.contentOffset = CGPointMake(maxXOffset, 0);
            // scrollBounds.origin = CGPointMake(maxXOffset, 0);
        }
        [scrollView setBounds:scrollBounds];
    }
    self.lastPosition = scrollView.contentOffset.x;
}

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{
    /* Need to calculate max/min offset for *every* page, not just the first and last. */
    CGFloat minXOffset = scrollView.bounds.size.width - (self.currentIndex * scrollView.bounds.size.width);
    CGFloat maxXOffset = (([viewControllers count] - self.currentIndex) * scrollView.bounds.size.width);

    if (!self.shouldBounce) {
        if (scrollView.contentOffset.x <= minXOffset) {
            *targetContentOffset = CGPointMake(minXOffset, 0);
        } else if (scrollView.contentOffset.x >= maxXOffset) {
            *targetContentOffset = CGPointMake(maxXOffset, 0);
        }
    }
}

基本上，它记录每个滚动事件的偏移量。如果滚动位置在与滚动方向相反的方向上移动了一个不可能的距离（我随意选择了屏幕宽度的90％），则代码将假定iOS对我们说谎，并且行为就像过渡正确完成，将偏移量视为相对于新页面而不是旧页面。