如何将UIPageControl作为 UIViewController的容器

在最新的iOS版本中(5.0 现在已经不是最新的)，Apple公司提供了很多如何用其他方式实现

UIViewController容器的方式(可以从这里参考)，但悲剧的是它们与 UIPageControl 没多大关系。

那么我们今天就来专门解决这个问题。

创建界面

首先我们需要在 Interface Builder 中在一个UIViewController里面创建一个UIPageControl与UIScrollView。当然你可以创建很多类似的UIViewController。

设置 PageViewController 类

这里的 PageViewController 对象将包含一个 UIScrollView 与一个 UIPageControl。而且 UIScrollView 将会包含所有的 subview, 这些subview就是被UIPageControl控制的子页面。

你也许会在 viewController 中添加一些算法来专门处理页面转换: addChildViewController:方法。然而在我这个案例中却不是这么做的，来一起看看代码：

1 @interface  PagerViewController : UIViewController
2
3 @property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
4 @property (nonatomic, strong) IBOutlet UIPageControl *pageControl;
5
6 - (IBAction)changePage:(id)sender;
7  @end

在实现的代码文件中，首先我先不让它能够旋转屏幕。然后当 PagerViewController 预备显示时，我们需要标记一下当前哪一个view是被激活的，即被显示的，那么需要在 viewDidApplear 以及 viewWillDisappear方法中加入以下代码：

01 - (BOOL)automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers {
02     return NO;
03 }
04
05 - (void)viewDidAppear:(BOOL)animated {
06     [super viewDidAppear:animated];
07     UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
08     if (viewController.view.superview != nil) {
09         [viewController viewDidAppear:animated];
10     }
11 }
12
13 - (void)viewWillDisappear:(BOOL)animated {
14     UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
15     if (viewController.view.superview != nil) {
16         [viewController viewWillDisappear:animated];
17     }
18     [super viewWillDisappear:animated];
19 }
20
21 - (void)viewDidDisappear:(BOOL)animated {
22     UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
23     if (viewController.view.superview != nil) {
24         [viewController viewDidDisappear:animated];
25     }
26     [super viewDidDisappear:animated];
27 }

viewWillAppear 可能会有点复杂，因为我们也需要加载所有的子view到 scrollView中，而且必须确保scrollview的contentsize比子view要大。

01 - (void)viewWillAppear:(BOOL)animated {
02     [super viewWillAppear:animated];
03
04     for (NSUInteger i =0; i < [self.childViewControllers count]; i++) {
05         [self loadScrollViewWithPage:i];
06     }
07
08     self.pageControl.currentPage = 0;
09     _page = 0;
10     [self.pageControl setNumberOfPages:[self.childViewControllers count]];
11
12     UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
13     if (viewController.view.superview != nil) {
14         [viewController viewWillAppear:animated];
15     }
16
17     self.scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * [self.childViewControllers count], scrollView.frame.size.height);
18 }

为了将UIViewController的内容加载到UIScrolView的contentView中，需要如下代码:

01 - (void)loadScrollViewWithPage:(int)page {
02     if (page < 0)
03         return;
04     if (page >= [self.childViewControllers count])
05         return;
06
07     // replace the placeholder if necessary
08     UIViewController *controller = [self.childViewControllers objectAtIndex:page];
09     if (controller == nil) {
10         return;
11     }
12
13     // add the controller's view to the scroll view
14     if (controller.view.superview == nil) {
15         CGRect frame = self.scrollView.frame;
16         frame.origin.x = frame.size.width * page;
17         frame.origin.y = 0;
18         controller.view.frame = frame;
19         [self.scrollView addSubview:controller.view];
20     }
21 }

处理滚动

为了处理滚动，我们需要实现几个 UIScrollViewDelegate 的方法以及尽早声明方法 - (IBAction)changePage:(id)sender

首先必须先知道滚动是如何实现的，要么是手势，要么就是点击了 UIPageControl 的一侧。

来一起看看下面的代码：

01 // At the begin of scroll dragging, reset the boolean used when scrolls originate from the UIPageControl
02 - (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
03          _pageControlUsed = NO;
04 }
05
06 // At the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
07 - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
08          _pageControlUsed = NO;
09 }
10
11 - (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
12         UIViewController *oldViewController = [self.childViewControllers objectAtIndex:_page];
13         UIViewController *newViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
14         [oldViewController viewDidDisappear:YES];
15         [newViewController viewDidAppear:YES];
16
17         _page = self.pageControl.currentPage;
18 }

现在，为了当页面改变时也能更新当前的显示，我们只需要实现 scrollViewDidScroll delegate方法以及 changePage IBAction 方法。

01 - (IBAction)changePage:(id)sender {
02         int page = ((UIPageControl *)sender).currentPage;
03
04         // update the scroll view to the appropriate page
05         CGRect frame = self.scrollView.frame;
06         frame.origin.x = frame.size.width * page;
07         frame.origin.y = 0;
08
09         UIViewController *oldViewController = [self.childViewControllers objectAtIndex:_page];
10         UIViewController *newViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
11         [oldViewController viewWillDisappear:YES];
12         [newViewController viewWillAppear:YES];
13
14         [self.scrollView scrollRectToVisible:frame animated:YES];
15
16         // Set the boolean used when scrolls originate from the UIPageControl. See scrollViewDidScroll: above.
17         _pageControlUsed = YES;
18 }
19
20 - (void)scrollViewDidScroll:(UIScrollView *)sender {