blocks|key|688138|text|当用户翻页时，将调用UIPageViewController的setViewControllers:方法。此方法接收UIPageViewControllerNavigationDirection类型的参数，该参数将为您提供所需的信息。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|688139|entityMap^0|V|J|1M|13|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

When the user turns a page the UIPageViewController's <code>setViewControllers:</code> method will be called. This method receives an argument of type <code>UIPageViewControllerNavigationDirection</code> that will give you the information you need.

blocks|key|472000|text|“基于页面的应用程序”模板提供了以下两种方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|472001|-+(NSUInteger)indexOfViewController:(DataViewController+*)viewController;+|code-block|syntax|javascript|472002|一种用于查找给定视图控制器的索引的方法|472003|-+(DataViewController+*)viewControllerAtIndex:(NSUInteger)index|472004|一种在给定索引的情况下实例化视图控制器的方法。|472005|为了制作正确的动画，您需要知道当前视图控制器的索引。基于页面的模板方法非常适合这一点。然后，您只需比较您的“跳转到”索引和您的“当前”索引。|472006|这里有一些代码来理解这个想法：|472007|-+(void)jumpToPage:(NSInteger)page+{++++
+++//+find+current+index
+++DataViewController+*currentViewController+=+(DataViewController+*)[self.pageViewController.viewControllers+lastObject];
+++NSUInteger+index+=+[self+indexOfViewController:currentViewController];

+++//+choosing+the+correct+direction
+++//+if+the+'current'+is+smaller+than+the+'jump+to'+page,+then+choose+forward
+++//+vice+versa
+++UIPageViewControllerNavigationDirection+direction;
+++if+(index+<+page)+{
+++++++direction+=+UIPageViewControllerNavigationDirectionForward;
+++}+else+{
+++++++direction+=+UIPageViewControllerNavigationDirectionReverse;
+++}

+++//+choose+view+controllers+according+to+the+orientation
+++NSArray+*viewControllers;
+++if+(UIInterfaceOrientationIsPortrait(self.interfaceOrientation))+{
+++++++DataViewController+*rightViewController+=+[self+viewControllerAtIndex:page];
+++++++viewControllers+=+[NSArray+arrayWithObject:rightViewController];
+++}+else+{
+++++++DataViewController+*rightViewController+=+[self+viewControllerAtIndex:page];
+++++++DataViewController+*leftViewController+=+[self+viewControllerAtIndex:page-1];
+++++++viewControllers+=+[NSArray+arrayWithObjects:leftViewController,+rightViewController,+nil];
+++}

+++//+fire+the+method+which+actually+trigger+the+animation
+++[self.pageViewController+setViewControllers:viewControllers+
+++++++++++++++++++++++++++++++++++++direction:direction+
++++++++++++++++++++++++++++++++++++++animated:YES+
++++++++++++++++++++++++++++++++++++completion:nil];
}|472008|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|10|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

The 'Page-Based Application' template provide these 2 methods : 

<pre><code>- (NSUInteger)indexOfViewController:(DataViewController *)viewController; 
</code></pre>

a method for finding index given a view controller 

<pre><code>- (DataViewController *)viewControllerAtIndex:(NSUInteger)index
</code></pre>

a method for instantiating a view controller given an index.

For making the correct animation, you need to know the index of your current view controller. The page-based template methods are perfect fit for that. Then, you simply compare your 'jump to' index and your 'current' index.

Here's some code to get the idea :

<pre><code>- (void)jumpToPage:(NSInteger)page { 
 // find current index
 DataViewController *currentViewController = (DataViewController *)[self.pageViewController.viewControllers lastObject];
 NSUInteger index = [self indexOfViewController:currentViewController];

 // choosing the correct direction
 // if the 'current' is smaller than the 'jump to' page, then choose forward
 // vice versa
 UIPageViewControllerNavigationDirection direction;
 if (index &lt; page) {
 direction = UIPageViewControllerNavigationDirectionForward;
 } else {
 direction = UIPageViewControllerNavigationDirectionReverse;
 }

 // choose view controllers according to the orientation
 NSArray *viewControllers;
 if (UIInterfaceOrientationIsPortrait(self.interfaceOrientation)) {
 DataViewController *rightViewController = [self viewControllerAtIndex:page];
 viewControllers = [NSArray arrayWithObject:rightViewController];
 } else {
 DataViewController *rightViewController = [self viewControllerAtIndex:page];
 DataViewController *leftViewController = [self viewControllerAtIndex:page-1];
 viewControllers = [NSArray arrayWithObjects:leftViewController, rightViewController, nil];
 }

 // fire the method which actually trigger the animation
 [self.pageViewController setViewControllers:viewControllers 
 direction:direction 
 animated:YES 
 completion:nil];
}
</code></pre>

blocks|key|472058|text|在手势驱动的转换完成后，此委托method被调用：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|472059|pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:|code-block|syntax|javascript|472060|因此，通过比较previousViewControllers参数和pageViewController.viewControllers，您可以知道方向。|style|CODE|472061|entityMap|0|LINK|mutability|MUTABLE|url|http://developer.apple.com/library/IOs/documentation/UIKit/Reference/UIPageViewControllerDelegateProtocolRef/UIPageViewControllerDelegate.html#//apple_ref/occ/intfm/UIPageViewControllerDelegate/pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:^0|F|6|0|0|0|7|N|X|Y|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@$A|V|B|W|1|X]]|C|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|Z|8|@$A|10|B|11|K|L]|$A|12|B|13|K|L]]|9|@]|C|$]]|$1|M|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|N|$O|$5|P|Q|R|C|$S|T]]]]

After a gesture-driven transition completes this delegate <a href="http://developer.apple.com/library/IOs/documentation/UIKit/Reference/UIPageViewControllerDelegateProtocolRef/UIPageViewControllerDelegate.html#//apple_ref/occ/intfm/UIPageViewControllerDelegate/pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:" rel="noreferrer">method</a> is called:

<pre><code>pageViewController:didFinishAnimating:previousViewControllers:transitionCompleted:
</code></pre>

So by comparing the <code>previousViewControllers</code> parameter and <code>pageViewController.viewControllers</code> you can know the direction.

blocks|key|472133|text|您可以将"pageIndex“属性添加到用作页面的视图控制器中。换句话说，当你为viewControllerBeforeViewController+&+viewControllerAfterViewController创建视图控制器时(或者当你调用setViewControllers时)，在这些视图控制器中存储一个pageIndex，然后当你需要知道索引的时候就可以引用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|472134|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

You could add a "pageIndex" property to your view controllers that serve as the pages. IOW, when you create the view controllers for viewControllerBeforeViewController &amp; viewControllerAfterViewController (or when you call setViewControllers), store a pageIndex in those view controllers that you can then reference whenever you need to know the index.

blocks|key|688321|text|页面控制器处理的很好的答案。我发现作为页面添加的视图控制器将在用户将页面滑入视图时调用viewWillAppear，并在完成时调用viewDidAppear。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|688322|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

great answers for page controller handling. I found that the view controller that was added as a page will call viewWillAppear as the user slides the page into view and will also call viewDidAppear upon completion.

I have a UIPageViewController and I just can not figure out how to know to what direction the user turned the page so i can set the page count appropriately.

Thanks
Shani

How can i know if UIPageViewController flipped forward or reversed?

我有一个UIPageViewController，我只是不知道如何知道用户将页面翻到了什么方向，这样我才能适当地设置页面计数。谢谢沙尼

问我如何知道UIPageViewController是向前翻转还是向后翻转？
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