如何将UIPageControl作为 UIViewController的容器

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虽然看上去用 UIPageControl 在一系列 UIView或UIViewController中导航是很平常的事情，但实际上Apple公司并没有提供一个这样的方法或者演示Demo:

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 {
21    // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
22    // which a scroll event generated from the user hitting the page control triggers updates from
23    // the delegate method. We use a boolean to disable the delegate logic when the page control is used.
24    if (_pageControlUsed || _rotating) {
25        // do nothing - the scroll was initiated from the page control, not the user dragging
26        return;
27    }
28  
29    // Switch the indicator when more than 50% of the previous/next page is visible
30        CGFloat pageWidth = self.scrollView.frame.size.width;
31        int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
32        if (self.pageControl.currentPage != page) {
33                UIViewController *oldViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
34                UIViewController *newViewController = [self.childViewControllers objectAtIndex:page];
35                [oldViewController viewWillDisappear:YES];
36                [newViewController viewWillAppear:YES];
37                self.pageControl.currentPage = page;
38                [oldViewController viewDidDisappear:YES];
39                [newViewController viewDidAppear:YES];
40                _page = page;
41        }
42}

最后处理旋转

首先在shouldAutorotateToInterfaceOrientation方法中返回 YES，同时也需要传输一下3个消息给当前被显示的子 UIViewController。

willAnimateRotationToInterfaceOrientation:duration:

willRotateToInterfaceOrientation:duration:

didRotateFromInterfaceOrientation:

但我们还是要自己处理旋转的问题，比如要重新缩放scrollview的contentView，以及调整子view的帧率，否则会出现一些无法预料的事情。所以来看看以下处理方式

01- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
02{
03    return YES;
04}
05  
06- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
07    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
08    [viewController willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];
09    _rotating = YES;
10}
11  
12- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
13  
14    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
15    [viewController willAnimateRotationToInterfaceOrientation:toInterfaceOrientation duration:duration];
16  
17    self.scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * [self.childViewControllers count], scrollView.frame.size.height);
18    NSUInteger page = 0;
19    for (viewController in self.childViewControllers) {
20        CGRect frame = self.scrollView.frame;
21        frame.origin.x = frame.size.width * page;
22        frame.origin.y = 0;
23        viewController.view.frame = frame;
24        page++;
25    }
26  
27    CGRect frame = self.scrollView.frame;
28    frame.origin.x = frame.size.width * _page;
29    frame.origin.y = 0;
30    [self.scrollView scrollRectToVisible:frame animated:NO];
31  
32}
33  
34- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
35    _rotating = NO;
36    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
37    [viewController didRotateFromInterfaceOrientation:fromInterfaceOrientation];
38}

总结

废话少说，这里放出代码，在GitHub上