基於分頁導航實現
在iOS 5之後，可以使用分頁控制器（UIPageViewController）構建類似於電子書效果的應用，我們稱為基於分頁的應用。一個分頁應用有很多相關的視圖控制器
分頁控制器（PageViewController）需要放置在一個父視圖控制器中，在分頁控制器下面還要有子視圖控制器，每個子視圖控制器對應圖中的一個頁面。
在基於分頁導航實現的應用中需要的類和協議：UIPageViewControllerDataSource協議和UIPageViewControllerDelegate協議和UIPageViewController類，UIPageViewController沒有對應的視圖類。
UIPageViewControllerDelegate委托協議中，最重要的方法為pageViewController:spineLocationForInterfaceOrientation:，它根據屏幕旋轉方向設置書脊位置（Spine Location）和初始化首頁。
UIPageViewController中有兩個常用的屬性：雙面顯示（doubleSided)和書脊位置（spineLocation）。
1.雙面顯示，是在頁面翻起的時候，偶數頁面會在背面顯示。圖6-13右圖為doubleSided設置為YES情況，圖6-14中圖為doubleSided設置為NO（單面顯示），單面顯示在頁面翻起的時候，能夠看到頁面的背面，背面的內容是當前頁面透過去的，與當前內容是相反的鏡像。
2.書脊位置。書脊位置也是很重要的屬性，但是它的spineLocation 屬性是只讀的，要設置它，需要通過UIPageViewControllerDelegate委托協議中的pageViewController:spineLocationForInterfaceOrientation:方法。書脊位置由枚舉UIPageViewControllerSpineLocation定義，該枚舉類型下的成員變量如下所示。
下面我們使用頁面導航實現城市信息這個應用。使用Single View Application模板創建一個名為 PageNavigation的工程。
可以從PageControlNavigation工程中復制過來，方法是在打開MainStoryboard.storyboard選中3個視圖控制器，按下Command+C組合鍵拷貝，再到PageNavigation中打開MainStoryboard.storyboard，按下Command+V組合鍵粘貼，就可以了。
這樣UI設計工作就結束了，下面的工作都是由代碼完成的。我們先看看ViewController.h的代碼：
[cpp]
#import <UIKit/UIKit.h>
@interface ViewController : UIViewController <UIPageViewControllerDataSource,UIPageViewControllerDelegate>
{
//當前頁面的索引
int pageIndex;
}
@property (strong, nonatomic) UIPageViewController *pageViewController;
@end
#import <UIKit/UIKit.h>
@interface ViewController : UIViewController <UIPageViewControllerDataSource,UIPageViewControllerDelegate>
{
//當前頁面的索引
int pageIndex;
}
@property (strong, nonatomic) UIPageViewController *pageViewController;
@end
在上述代碼中，ViewController實現了UIPageViewControllerDataSource和UIPageViewControllerDelegate協議。成員變量pageIndex保存了當前頁面的索引，pageViewController屬性保存了UIPageViewController實例。
下面我們看看程序代碼ViewController.m的viewDidLoad方法：
[cpp]
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.frame = CGRectMake(0.0f, 0.0f, 320.0f, 440.0f);
self.pageViewController = [[UIPageViewController alloc]
initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl
navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
self.pageViewController.delegate = self;
self.pageViewController.dataSource = self;
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController* page1ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page1"];
//第一個視圖，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
[self addChildViewController:self.pageViewController];
[self.view addSubview:self.pageViewController.view];
pageIndex = 0;
}
- (void)viewDidLoad
{
[super viewDidLoad];
self.view.frame = CGRectMake(0.0f, 0.0f, 320.0f, 440.0f);
self.pageViewController = [[UIPageViewController alloc]
initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl
navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
self.pageViewController.delegate = self;
self.pageViewController.dataSource = self;
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController* page1ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page1"];
//第一個視圖，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
[self addChildViewController:self.pageViewController];
[self.view addSubview:self.pageViewController.view];
pageIndex = 0;
}
在上述代碼中，initWithTransitionStyle:navigationOrientation:options:構造方法用於創建UIPageViewController實例，initWithTransitionStyle用於設定頁面翻轉的樣式。UIPageViewControllerTransitionStyle枚舉類型定義了如下兩個翻轉樣式。
UIPageViewControllerTransitionStylePageCurl：翻書效果樣式。
UIPageViewControllerTransitionStyleScroll：滑屏效果樣式。
navigationOrientation設定了翻頁方向，UIPageViewControllerNavigationDirection枚舉類型定義了以下兩種翻頁方式。
UIPageViewControllerNavigationDirectionForward：從左往右（或從下往上）；
UIPageViewControllerNavigationDirectionReverse：從右向左（或從上往下）。
代碼NSArray *viewControllers = @[page1ViewController]相當於NSArray *viewControllers = [NSArray arrayWithObject: page1ViewController , nil]。
在UIPageViewController中，setViewControllers:direction:animated:completion:方法用於設定首頁中顯示的視圖。首頁中顯示幾個視圖與書脊類型有關，如果是UIPageViewControllerSpineLocationMin或UIPageViewControllerSpineLocationMax，首頁中顯示一個視圖；如果是UIPageViewControllerSpineLocationMid，首頁中顯示兩個視圖。
[self addChildViewController:self.pageViewController]語句是將PageViewController添加到父視圖控制器中去。
我們再看看ViewController.m中有關數據源UIPageViewControllerDataSource協議實現方法的代碼：
[cpp] view plaincopyprint?- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerBeforeViewController:(UIViewController *)viewController
{
pageIndex–;
if (pageIndex < 0){
pageIndex = 0;
return nil;
}
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
NSString *pageId = [NSString stringWithFormat:@"page%i",pageIndex+1];
UIViewController* pvController = [mainStoryboard instantiateViewControllerWithIdentifier:pageId];
return pvController;
}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerAfterViewController:(UIViewController *)viewController
{
pageIndex++;
if (pageIndex > 2){
pageIndex = 2;
return nil;
}
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
NSString *pageId = [NSString stringWithFormat:@"page%i",pageIndex+1];
UIViewController* pvController = [mainStoryboard instantiateViewControllerWithIdentifier:pageId];
return pvController;
}
在ViewController.m中，有關委托協議UIPageViewControllerDelegate實現方法的代碼如下：
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController
spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMin;
}
由於spineLocation屬性是只讀的，所以只能在這個方法中設置書脊位置，該方法可以根據屏幕旋轉方向的不同來動態設定書脊的位置，實現代碼可以參考下面的代碼：
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController
spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController* page1ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page1"];
UIViewController* page2ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page2"];
if (orientation == UIInterfaceOrientationLandscapeLeft || orientation == UIInterfaceOrientationLandscapeRight)
{
//取出第一個視圖控制器，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController, page2ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMid;
}
//取出第一個視圖控制器，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMin;
}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerBeforeViewController:(UIViewController *)viewController
{
pageIndex–;
if (pageIndex < 0){
pageIndex = 0;
return nil;
}
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
NSString *pageId = [NSString stringWithFormat:@"page%i",pageIndex+1];
UIViewController* pvController = [mainStoryboard instantiateViewControllerWithIdentifier:pageId];
return pvController;
}
- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController
viewControllerAfterViewController:(UIViewController *)viewController
{
pageIndex++;
if (pageIndex > 2){
pageIndex = 2;
return nil;
}
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
NSString *pageId = [NSString stringWithFormat:@"page%i",pageIndex+1];
UIViewController* pvController = [mainStoryboard instantiateViewControllerWithIdentifier:pageId];
return pvController;
}
在ViewController.m中，有關委托協議UIPageViewControllerDelegate實現方法的代碼如下：
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController
spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMin;
}
由於spineLocation屬性是只讀的，所以只能在這個方法中設置書脊位置，該方法可以根據屏幕旋轉方向的不同來動態設定書脊的位置，實現代碼可以參考下面的代碼：
- (UIPageViewControllerSpineLocation)pageViewController:(UIPageViewController *)pageViewController
spineLocationForInterfaceOrientation:(UIInterfaceOrientation)orientation
{
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"MainStoryboard" bundle:nil];
UIViewController* page1ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page1"];
UIViewController* page2ViewController = [mainStoryboard instantiateViewControllerWithIdentifier:@"page2"];
if (orientation == UIInterfaceOrientationLandscapeLeft || orientation == UIInterfaceOrientationLandscapeRight)
{
//取出第一個視圖控制器，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController, page2ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMid;
}
//取出第一個視圖控制器，最為PageViewController首頁
NSArray *viewControllers = @[page1ViewController];
[self.pageViewController setViewControllers:viewControllers
direction:UIPageViewControllerNavigationDirectionForward animated:YES completion:NULL];
self.pageViewController.doubleSided = NO;
return UIPageViewControllerSpineLocationMin;
}
這只是一個基本的實現，要根據具體的應用具體再定。用平鋪導航實現時，UIPageViewController往往不需要實現屏幕旋轉的支持，而且書脊的位置也不會設置在中間。
代碼編寫完畢看效果。
