iphone - UIScrollViewDelegate 不触发

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和pagingEnabled。我想使用 UIScrollViewDelegate 来帮助检测我所在的页面。这是我的代码:

@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(@" ");

}

本质上，问题在于上面的两种方法scrollViewDidEndDeclerating和scrollViewDidScroll没有打印。换句话说，他们没有被召唤。

有任何想法吗？

最佳答案

问题在于语句的顺序:

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

您尝试在创建滚动 View 之前设置委托(delegate)，因此该语句无效，因为scroll是nil。改为执行此操作:

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

我刚刚注意到您的评论:

// 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，应在将它们添加到scrollView之后释放targetView，targetNameLabel和missionNameLabel。您拥有它们是因为它们是通过alloc-init创建的，并且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，它将按照addSubview:文档中的说明保留它们，以确保在scrollView需要它们时不会将它们释放。

关于iphone - UIScrollViewDelegate 不触发，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/6842568/