我有一个关于 UIPageViewController 的非常有趣的问题。
我的项目设置与基于页面的应用程序模板示例非常相似。
时不时地(但在一定程度上可重现)某个平移手势会调用 -(UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
。
我返回下一页的 View Controller ,但从未运行过翻页动画,也从未调用过我的委托(delegate)方法。
这是viewControllerAfterViewController
的代码
-(UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
{
PageDisplayViewController *vc = (PageDisplayViewController *)viewController;
NSUInteger index = [self.pageFetchController.fetchedObjects indexOfObject:vc.page];
if(index == (self.pageFetchController.fetchedObjects.count - 1)) return nil;
return [self getViewControllerForIndex:(++index)];
}
这是 getViewControllerForIndex:
-(PageDisplayViewController *)getViewControllerForIndex:(NSUInteger)index
{
PageDisplayViewController *newVC = [self.storyboard instantiateViewControllerWithIdentifier:@"PageDisplayController"];
newVC.page = [self.pageFetchController.fetchedObjects objectAtIndex:(index)];
newVC.view.frame = CGRectMake(0, 0, 1024, 604);
NSLog(@"%i", index);
if(index == 0)
{
//We're moving to the first, animate the back button to be hidden.
[UIView animateWithDuration:0.5 animations:^
{
self.backButton.alpha = 0.f;
} completion:^(BOOL finished){
self.backButton.hidden = YES;
}];
}
else if(index == (self.pageFetchController.fetchedObjects.count - 1))
{
[UIView animateWithDuration:0.5 animations:^{
self.nextButton.alpha = 0.f;
} completion:^(BOOL finished){
self.nextButton.hidden = YES;
}];
}
else
{
BOOL eitherIsHidden = self.nextButton.hidden || self.backButton.hidden;
if(eitherIsHidden)
{
[UIView animateWithDuration:0.5 animations:^{
if(self.nextButton.hidden)
{
self.nextButton.hidden = NO;
self.nextButton.alpha = 1.f;
}
if(self.backButton.hidden)
{
self.backButton.hidden = NO;
self.backButton.alpha = 1.f;
}
}];
}
}
return newVC;
}
基本上,我创建 View Controller ,设置它的数据对象,然后根据索引淡出下一步/后退按钮。
委托(delegate)方法
-(void)pageViewController:(UIPageViewController *)pageViewController didFinishAnimating:(BOOL)finished previousViewControllers:(NSArray *)previousViewControllers transitionCompleted:(BOOL)completed
{
PageDisplayViewController *vc = [previousViewControllers lastObject];
NSUInteger index = [self.pageFetchController.fetchedObjects indexOfObject:vc.page];
if (!completed)
{
[self.pagePreviewView setCurrentIndex:index];
NSLog(@"Animation Did not complete, reverting pagepreview");
}
else
{
PageDisplayViewController *curr = [pageViewController.viewControllers lastObject];
NSUInteger i = [self.pageFetchController.fetchedObjects indexOfObject:curr.page];
[self.pagePreviewView setCurrentIndex:i];
NSLog(@"Animation compeleted, updating pagepreview. Index: %u", i);
}
}
我只是注意到这个问题,因为我的后退按钮会随机地重新出现在屏幕上。在其中加入一些 NSLog()
语句后,我注意到我的 dataSource 方法被调用以获得索引 1,但是没有动画播放或委托(delegate)被调用。更可怕的是,如果我尝试平移下一页,索引 1 将再次被调用。
我担心这可能是 UIPageViewController 的错误。
最佳答案
由于我在第一个答案中仍然收到神秘的实现崩溃,我一直在寻找一个“足够好”的解决方案,该解决方案较少依赖于对页面 View Controller (PVC) 底层行为的个人假设。这是我想出的办法。
我以前的方法有点侵入性,更像是一种变通方法,而不是可接受的解决方案。与其对抗 PVC 以迫使它做我认为它应该做的事情,不如接受这样的事实:
pageViewController:viewControllerBeforeViewController:
和pageViewController:viewControllerAfterViewController:
方法可以被 UIKit 调用任意次数,并且- 绝对不能保证其中任何一个对应于分页动画,也不保证它们之后会调用
pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:
这意味着我们不能将 before/after 方法用作“动画开始”(但是请注意,didFinishAnimating
仍然用作“动画结束”事件)。那么我们怎么知道动画确实开始了呢?
根据我们的需要,我们可能对以下事件感兴趣:
用户开始摆弄页面: 一个很好的指标是前/后回调,或者更准确地说是第一个回调。
翻页手势的第一个视觉反馈: 我们可以在 PVC 的点击和平移手势识别器的
state
属性上使用 KVO。当观察到平移的UIGestureRecognizerStateBegan
值时,我们可以非常确定视觉反馈将随之而来。用户通过释放触摸来完成拖动页面: 再次,KVO。当
<UIGestureRecognizerStateRecognized
值被报告用于平移或点击时,PVC 将实际翻页,因此这可以用作“动画开始”。UIKit 启动分页动画: 我不知道如何获得对此的直接反馈。
UIKit 结束分页动画: 小菜一碟,只听
pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:
。
对于 KVO,只需抓取 PVC 的手势识别器,如下所示:
@interface MyClass () <UIGestureRecognizerDelegate>
{
UIPanGestureRecognizer* pvcPanGestureRecognizer;
UITapGestureRecognizer* pvcTapGestureRecognizer;
}
...
for ( UIGestureRecognizer* recognizer in pageViewController.gestureRecognizers )
{
if ( [recognizer isKindOfClass:[UIPanGestureRecognizer class]] )
{
pvcPanGestureRecognizer = (UIPanGestureRecognizer*)recognizer;
}
else if ( [recognizer isKindOfClass:[UITapGestureRecognizer class]] )
{
pvcTapGestureRecognizer = (UITapGestureRecognizer*)recognizer;
}
}
然后将您的类注册为 state
属性的观察者:
[pvcPanGestureRecognizer addObserver:self
forKeyPath:@"state"
options:NSKeyValueObservingOptionNew
context:NULL];
[pvcTapGestureRecognizer addObserver:self
forKeyPath:@"state"
options:NSKeyValueObservingOptionNew
context:NULL];
并实现通常的回调:
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
{
if ( [keyPath isEqualToString:@"state"] && (object == pvcPanGestureRecognizer || object == pvcTapGestureRecognizer) )
{
UIGestureRecognizerState state = [[change objectForKey:NSKeyValueChangeNewKey] intValue];
switch (state)
{
case UIGestureRecognizerStateBegan:
// trigger for visual feedback
break;
case UIGestureRecognizerStateRecognized:
// trigger for animation-begin
break;
// ...
}
}
}
完成后,不要忘记取消订阅这些通知,否则您的应用可能会出现泄漏和奇怪的崩溃:
[pvcPanGestureRecognizer removeObserver:self
forKeyPath:@"state"];
[pvcTapGestureRecognizer removeObserver:self
forKeyPath:@"state"];
这就是所有人!
关于ios - UIPageViewController 手势正在调用 viewControllerAfter : but doesn't animate,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/12533240/