如何將UIPageControl作為 UIViewController的容器

jopen 13年前發布 | 22K 次閱讀 IOS iOS開發移動開發

雖然看上去用 UIPageControl 在一系列 UIView或UIViewController中導航是很平常的事情，但實際上 Apple公司并沒有提供一個這樣的方法或者演示Demo:

在最新的iOS版本中(5.0 現在已經不是最新的)，Apple公司提供了很多如何用其他方式實現

UIViewController容器的方式(可以從這里參考)，但悲劇的是它們與 UIPageControl 沒多大關系。

那么我們今天就來專門解決這個問題。

創建界面

首先我們需要在 Interface Builder 中在一個UIViewController里面創建一個UIPageControl與UIScrollView。當然你可以創建很多類似的UIViewController。

設置 PageViewController 類

這里的 PageViewController 對象將包含一個 UIScrollView 與一個 UIPageControl。而且 UIScrollView 將會包含所有的 subview, 這些subview就是被UIPageControl控制的子頁面。

你也許會在 viewController 中添加一些算法來專門處理頁面轉換: addChildViewController:方法。然而在我這個案例中卻不是這么做的，來一起看看代碼：

@interface  PagerViewController : UIViewController 

@property (nonatomic, strong) IBOutlet UIScrollView *scrollView;
@property (nonatomic, strong) IBOutlet UIPageControl *pageControl;

- (IBAction)changePage:(id)sender;
 @end

在實現的代碼文件中，首先我先不讓它能夠旋轉屏幕。然后當 PagerViewController 預備顯示時，我們需要標記一下當前哪一個view是被激活的，即被顯示的，那么需要在 viewDidApplear 以及 viewWillDisappear方法中加入以下代碼：

- (BOOL)automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers {
    return NO;
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    if (viewController.view.superview != nil) {
        [viewController viewDidAppear:animated];
    }
}

- (void)viewWillDisappear:(BOOL)animated {
    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    if (viewController.view.superview != nil) {
        [viewController viewWillDisappear:animated];
    }
    [super viewWillDisappear:animated];
}

- (void)viewDidDisappear:(BOOL)animated {
    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    if (viewController.view.superview != nil) {
        [viewController viewDidDisappear:animated];
    }
    [super viewDidDisappear:animated];
}

viewWillAppear 可能會有點復雜，因為我們也需要加載所有的子view到 scrollView中，而且必須確保scrollview的contentsize比子view要大。

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];

    for (NSUInteger i =0; i < [self.childViewControllers count]; i++) {
        [self loadScrollViewWithPage:i];
    }

    self.pageControl.currentPage = 0;
    _page = 0;
    [self.pageControl setNumberOfPages:[self.childViewControllers count]];

    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    if (viewController.view.superview != nil) {
        [viewController viewWillAppear:animated];
    }

    self.scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * [self.childViewControllers count], scrollView.frame.size.height);
}

為了將UIViewController的內容加載到UIScrolView的contentView中，需要如下代碼:

- (void)loadScrollViewWithPage:(int)page {
    if (page < 0)
        return;
    if (page >= [self.childViewControllers count])
        return;

    // replace the placeholder if necessary
    UIViewController *controller = [self.childViewControllers objectAtIndex:page];
    if (controller == nil) {
        return;
    }

    // add the controller's view to the scroll view
    if (controller.view.superview == nil) {
        CGRect frame = self.scrollView.frame;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0;
        controller.view.frame = frame;
        [self.scrollView addSubview:controller.view];
    }
}

處理滾動

為了處理滾動，我們需要實現幾個 UIScrollViewDelegate 的方法以及盡早聲明方法 - (IBAction)changePage:(id)sender

首先必須先知道滾動是如何實現的，要么是手勢，要么就是點擊了 UIPageControl 的一側。

來一起看看下面的代碼：

// At the begin of scroll dragging, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {
         _pageControlUsed = NO;
}

// At the end of scroll animation, reset the boolean used when scrolls originate from the UIPageControl
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
         _pageControlUsed = NO;
}

- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView {
        UIViewController *oldViewController = [self.childViewControllers objectAtIndex:_page];
        UIViewController *newViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
        [oldViewController viewDidDisappear:YES];
        [newViewController viewDidAppear:YES];

        _page = self.pageControl.currentPage;
}

現在，為了當頁面改變時也能更新當前的顯示，我們只需要實現 scrollViewDidScroll delegate方法以及 changePage IBAction 方法。

- (IBAction)changePage:(id)sender {
        int page = ((UIPageControl *)sender).currentPage;

        // update the scroll view to the appropriate page
        CGRect frame = self.scrollView.frame;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0;

        UIViewController *oldViewController = [self.childViewControllers objectAtIndex:_page];
        UIViewController *newViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
        [oldViewController viewWillDisappear:YES];
        [newViewController viewWillAppear:YES];

        [self.scrollView scrollRectToVisible:frame animated:YES];

        // Set the boolean used when scrolls originate from the UIPageControl. See scrollViewDidScroll: above.
        _pageControlUsed = YES;
}

- (void)scrollViewDidScroll:(UIScrollView *)sender {
    // We don't want a "feedback loop" between the UIPageControl and the scroll delegate in
    // which a scroll event generated from the user hitting the page control triggers updates from
    // the delegate method. We use a boolean to disable the delegate logic when the page control is used.
    if (_pageControlUsed || _rotating) {
        // do nothing - the scroll was initiated from the page control, not the user dragging
        return;
    }

    // Switch the indicator when more than 50% of the previous/next page is visible
        CGFloat pageWidth = self.scrollView.frame.size.width;
        int page = floor((self.scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
        if (self.pageControl.currentPage != page) {
                UIViewController *oldViewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
                UIViewController *newViewController = [self.childViewControllers objectAtIndex:page];
                [oldViewController viewWillDisappear:YES];
                [newViewController viewWillAppear:YES];
                self.pageControl.currentPage = page;
                [oldViewController viewDidDisappear:YES];
                [newViewController viewDidAppear:YES];
                _page = page;
        }
}

最后處理旋轉

首先在shouldAutorotateToInterfaceOrientation方法中返回 YES，同時也需要傳輸一下3個消息給當前被顯示的子 UIViewController。

willAnimateRotationToInterfaceOrientation:duration:

willRotateToInterfaceOrientation:duration:

didRotateFromInterfaceOrientation:

但我們還是要自己處理旋轉的問題，比如要重新縮放scrollview的contentView，以及調整子view的幀率，否則會出現一些無法預料的事情。所以來看看以下處理方式

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

- (void)willRotateToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    [viewController willRotateToInterfaceOrientation:toInterfaceOrientation duration:duration];
    _rotating = YES;
}

- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {

    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    [viewController willAnimateRotationToInterfaceOrientation:toInterfaceOrientation duration:duration];

    self.scrollView.contentSize = CGSizeMake(scrollView.frame.size.width * [self.childViewControllers count], scrollView.frame.size.height);
    NSUInteger page = 0;
    for (viewController in self.childViewControllers) {
        CGRect frame = self.scrollView.frame;
        frame.origin.x = frame.size.width * page;
        frame.origin.y = 0;
        viewController.view.frame = frame;
        page++;
    }

    CGRect frame = self.scrollView.frame;
    frame.origin.x = frame.size.width * _page;
    frame.origin.y = 0;
    [self.scrollView scrollRectToVisible:frame animated:NO];

}

- (void)didRotateFromInterfaceOrientation:(UIInterfaceOrientation)fromInterfaceOrientation {
    _rotating = NO;
    UIViewController *viewController = [self.childViewControllers objectAtIndex:self.pageControl.currentPage];
    [viewController didRotateFromInterfaceOrientation:fromInterfaceOrientation];
}

總結

廢話少說，這里放出代碼，在GitHub上

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