编写简单的翻页效果

beike

 
http://marshal.easymorse.com/archives/3760
 
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：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:self action:@selector(handleSwipeFrom:)]; 
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionRight)]; 
    [[self view] addGestureRecognizer:recognizer]; 
    [recognizer release]; 
    
    recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeFrom:)]; 
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionUp)]; 
    [[self view] addGestureRecognizer:recognizer]; 
    [recognizer release]; 
    
    recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeFrom:)]; 
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionDown)];
    [[self view] addGestureRecognizer:recognizer]; 
    [recognizer release]; 
    
    recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeFrom:)]; 
    [recognizer setDirection:(UISwipeGestureRecognizerDirectionLeft)]; 
    [[self view] addGestureRecognizer:recognizer]; 
    [recognizer release]; 
    
    
    [super viewDidLoad];
 

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:UIViewAnimationTransitionCurlDown forView: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]; 
[UIView setAnimationTransition: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:[NSURL fileURLWithPath:path] error:NULL]; 
    
    //[[UIApplication sharedApplication] setStatusBarHidden:YES animated:NO]; 
    [[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation: UIStatusBarAnimationSlide]; 
    UIImageView *contentView = [[UIImageView alloc] initWithFrame:[[UIScreen mainScreen] applicationFrame]];  
    [contentView setImage:[UIImage imageNamed:[pages objectAtIndex:(currentTag-1)]]];  
    [contentView setUserInteractionEnabled: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:[[UIScreen mainScreen] applicationFrame]]; 
    [contentView setImage:[UIImage imageNamed:[pages objectAtIndex:(currentTag-1)]]];  
    [contentView setUserInteractionEnabled:YES]; 
    contentView.tag=currentTag; 
    
    [UIView beginAnimations:@"animationID" context:nil]; 
    [UIView setAnimationDuration:0.7f]; 
    [UIView setAnimationCurve:UIViewAnimationCurveEaseInOut]; 
    [UIView setAnimationRepeatAutoreverses:NO]; 
    [UIView setAnimationTransition:UIViewAnimationTransitionCurlUp forView:self.view cache:YES]; 
    
    [currentView removeFromSuperview]; 
    [self.view addSubview:contentView]; 
    
    [UIView commitAnimations];