UIScrollViewDelegate not firing

Question

这可能是一些sort of duplicate of this question。但我试图应用它的答案无济于事。

我有一个UIScrollView与pagingEnabled。我想用UIScrollViewDelegate来帮助检测我在哪个页面上。这里是我的代码：

@interface SearchMissionViewController : UIViewController <UIScrollViewDelegate> { 

    UIScrollView *scroll; 

} 
    @property (nonatomic, retain) UIScrollView *scroll; 

    - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView; 
    - (void)scrollViewDidScroll:(UIScrollView *)scrollView; 
    - (IBAction) popView; 


    @end 




- (void)viewDidLoad 
{ 
    [super viewDidLoad] ; 

    // Here I have also tried scroll.delegate = self; 
    self.scroll.delegate = self; 


    self.view.backgroundColor = [UIColor redColor]; 
    scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; 

    // Is this correct? I've added it to try to get the UIScrollView Delegate calling scrollViewDidEndScrollingAnimation (or whatever) 
    // [scroll setContentOffset:CGPointMake(0.0, 0.0) animated:YES]; 


    scroll.pagingEnabled = YES; 
    NSInteger numberOfViews = 3; 
    for (int i = 0; i < numberOfViews; i++) { 
     CGFloat yOrigin = i * self.view.frame.size.width; 
     UIView *awesomeView = [[UIView alloc] initWithFrame:CGRectMake(yOrigin, 0, self.view.frame.size.width, self.view.frame.size.height)]; 
     awesomeView.backgroundColor = [UIColor colorWithRed:0.9 green:0.9 blue:0.9 alpha:1]; 


     UIImageView *targetView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"targetImageA.png"]]; 
     targetView.frame = CGRectMake(0.0, 0.0, 139, 153); 
     targetView.frame = CGRectMake(yOrigin+90 , 80, 139, 153); 


     UILabel *targetNameLabel = [[UILabel alloc] initWithFrame:CGRectMake(yOrigin+95, 230, 100, 20)]; 
     targetNameLabel.text = @"Bond"; 
     targetNameLabel.backgroundColor = [UIColor clearColor]; 
     targetNameLabel.textColor = [UIColor redColor]; 


     UILabel *missionNameLabel = [[UILabel alloc] initWithFrame:CGRectMake(yOrigin+95, 250, 100, 20)]; 
     missionNameLabel.text = @"Mission"; 
     missionNameLabel.backgroundColor = [UIColor clearColor]; 
     missionNameLabel.textColor = [UIColor redColor]; 



     [scroll addSubview:awesomeView];   
     [scroll addSubview:targetView]; 
     [scroll addSubview:targetNameLabel]; 
     [scroll addSubview:missionNameLabel]; 

     // Why does this get released? Wouldn't it then dissappear from the scroll view? Should I not be releasing other objects from above? 
     [awesomeView release]; 


    } 
    scroll.contentSize = CGSizeMake(self.view.frame.size.width * numberOfViews, self.view.frame.size.height); 
    [self.view addSubview:scroll]; 
    [scroll release]; 




    // Overlap image 
    UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 0, 320, 460)]; 
    imgView.image= [UIImage imageNamed:@"mission-viewfinder.png"]; 
    [self.view addSubview:imgView]; 


    // Place back button ontop of the image. 
    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom ]; 
    [button addTarget:self 
       action:@selector(popView) 
    forControlEvents:UIControlEventTouchDown]; 
    button.frame = CGRectMake(0.0, 0.0, 100.0, 60.0); 
    [self.view addSubview:button]; 


    // Do any additional setup after loading the view from its nib. 
} 








- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView 
{ 
    NSLog(@" "); 
    NSLog(@" Scroll View Did End Decelerating"); 
    NSLog(@" "); 

} 



- (void)scrollViewDidScroll:(UIScrollView *)scrollView 
{ 
    NSLog(@" "); 
    NSLog(@" Scroll View Did End Scroll ! ! ! "); 
    NSLog(@" "); 

} 

本质的问题是，这两种方法之上，scrollViewDidEndDeclerating和scrollViewDidScroll不打印。换句话说，他们没有被召唤。

任何想法？

Answer 1

问题就出在语句的顺序：

self.scroll.delegate = self; 
... 
scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; 

试图为委托创建滚动视图之前，所以语句没有影响，因为scroll是nil。做到这一点，而不是：

self.scroll = [[[UIScrollView alloc] initWithFrame:CGRectMake(...)] autorelease]; 
self.scroll.delegate = self; 

---

我刚才注意到您的评论：

// Why does this get released? Wouldn't it then dissappear from the scroll view? Should I not be releasing other objects from above? 
[awesomeView release]; 

是的，你应该释放targetView，targetNameLabel和missionNameLabel将它们添加到了滚动后。你拥有它们是因为你创建了它们（通过alloc-init），你必须通过向它们发送release消息来放弃它们的所有权。当您将它们添加到scrollView时，它将保留它们，如addSubview:文档中所述，以确保它们在scrollView需要时不会被释放。

Answer 2

而不是

- (void)viewDidLoad 
{ 
    // Here I have also tried scroll.delegate = self; 
    self.scroll.delegate = self; 
    self.view.backgroundColor = [UIColor redColor]; 
    scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; 
} 

你应该这样做

- (void)viewDidLoad 
{ 
    self.view.backgroundColor = [UIColor redColor]; 
    scroll = [[UIScrollView alloc] initWithFrame:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)]; 

    self.scroll.delegate = self; 
}