翻页效果，类似下面的样子：

在电子书应用中会很常见。这里需要两个要点：

• 翻页动画
• 手势上下轻扫（swipe）的处理

先说一下轻扫（swipe）的实现，可以参考编写简单的手势示例：Tap了解手势种类。

在viewDidLoad方法中注册了对上、下、左、右四个方向轻松的处理方法：

- (void)viewDidLoad {

UISwipeGestureRecognizer *recognizer;

recognizer =[[UISwipeGestureRecognizer alloc] initWithTarget:selfaction:@selector(handleSwipeFrom:)];
[recognizersetDirection:(UISwipeGestureRecognizerDirectionRight)];
[[self view]addGestureRecognizer:recognizer];
[recognizerrelease];

recognizer =[[UISwipeGestureRecognizer alloc] initWithTarget:selfaction:@selector(handleSwipeFrom:)];
[recognizersetDirection:(UISwipeGestureRecognizerDirectionUp)];
[[self view]addGestureRecognizer:recognizer];
[recognizerrelease];

recognizer =[[UISwipeGestureRecognizer alloc] initWithTarget:selfaction:@selector(handleSwipeFrom:)];
[recognizersetDirection:(UISwipeGestureRecognizerDirectionDown)];
[[self view]addGestureRecognizer:recognizer];
[recognizerrelease];

recognizer =[[UISwipeGestureRecognizer alloc] initWithTarget:selfaction:@selector(handleSwipeFrom:)];
[recognizersetDirection:(UISwipeGestureRecognizerDirectionLeft)];
[[self view]addGestureRecognizer:recognizer];
[recognizerrelease];


[superviewDidLoad];

可以看到，都是同一个方法，handleSwipeFrom。

在该方法中，再识别具体是哪个方向的轻扫手势，比如判断是向下的轻扫：

-(void)handleSwipeFrom:(UISwipeGestureRecognizer *)recognizer{
NSLog(@"Swipe received.");

if(recognizer.direction==UISwipeGestureRecognizerDirectionDown){
NSLog(@"swipe down");

判断是向上的轻扫：

if (recognizer.direction==UISwipeGestureRecognizerDirectionUp){
NSLog(@"swipe up");

有关动画的处理，比如向下（往回）翻页，类似这样：

[UIView beginAnimations:@"animationID" context:nil];
[UIView setAnimationDuration:0.7f];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationRepeatAutoreverses:NO];
[UIView setAnimationTransition:UIViewAnimationTransitionCurlDownforView:self.view cache:YES];

[currentView removeFromSuperview];
[self.view addSubview:contentView];

[UIView commitAnimations];

向上（向前）翻页，只需改为：

[UIView beginAnimations:@"animationID" context:nil];
[UIView setAnimationDuration:0.7f];
[UIView setAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIView setAnimationRepeatAutoreverses:NO];
[UIViewsetAnimationTransition:UIViewAnimationTransitionCurlUpforView:self.view cache:YES];

[currentView removeFromSuperview];
[self.view addSubview:contentView];

[UIView commitAnimations];

如果是电子书，还需要考虑一个问题，就是有多个页面（图形），比如50页。那么需要有一个数据结构来保存这些页面的图片路径：

• objc数据结构，比如数组
• sqlite数据库表

这样，写一套翻页代码和加载什么图形之间就可以解耦。

本文示例使用的是数组，类似这样：

pages=[[NSArray alloc]initWithObjects:@"1.jpg",@"2.jpg",@"3.jpg",@"4.jpg",@"5.jpg",@"6.jpg",
nil];

图片保存在resources下。

为了能让上页下页翻页的时候找到关联的页面，采用了如下机制：

• 将图片封装为UIImageView显示
• 可以为UIImageView设置一个tag值，值为数组下标+1
• 这样，上级view有方法能根据tag查询到UIImageView，比如：UIView*currentView=[self.view viewWithTag:currentTag];
• 设置一个成员变量currentTag保存当前的tag值

比如这样，当应用加载的时候显示第一页：

currentTag=1;

NSString*path = [[NSBundle mainBundle] pathForResource:@"pageflip1"ofType:@"mp3"];
player=[[AVAudioPlayer alloc] initWithContentsOfURL:[NSURLfileURLWithPath:path] error:NULL];

//[[UIApplication sharedApplication] setStatusBarHidden:YESanimated:NO];
[[UIApplication sharedApplication] setStatusBarHidden:YESwithAnimation: UIStatusBarAnimationSlide];
UIImageView*contentView = [[UIImageView alloc] initWithFrame:[[UIScreenmainScreen] applicationFrame]];
[contentViewsetImage:[UIImage imageNamed:[pagesobjectAtIndex:(currentTag-1)]]];
[contentViewsetUserInteractionEnabled:YES];
contentView.tag=currentTag;

在翻页时的处理：

if (currentTag<[pages count]) {
UIView*currentView=[self.view viewWithTag:currentTag];
currentTag++;

UIImageView*contentView = [[UIImageView alloc] initWithFrame:[[UIScreenmainScreen] applicationFrame]];
[contentViewsetImage:[UIImage imageNamed:[pagesobjectAtIndex:(currentTag-1)]]];
[contentViewsetUserInteractionEnabled:YES];
contentView.tag=currentTag;

[UIViewbeginAnimations:@"animationID" context:nil];
[UIViewsetAnimationDuration:0.7f];
[UIViewsetAnimationCurve:UIViewAnimationCurveEaseInOut];
[UIViewsetAnimationRepeatAutoreverses:NO];
[UIViewsetAnimationTransition:UIViewAnimationTransitionCurlUpforView:self.view cache:YES];

[currentViewremoveFromSuperview];
[self.viewaddSubview:contentView];

[UIViewcommitAnimations];