使用UITapGestureRecognizer

Question

iPhone开发新手 我有一个视图,其中包含一个包含UIImageView的UIScrollView.我在图像视图上添加了一个(双)轻击手势识别器,使警报框打开.出于某种原因,我确信我只是迟钝,它开了3次.

这是我的代码:

- (void)viewDidLoad {

    scrollView.delegate = self;

    UIImage* image = imageView.image;
    imageView.bounds = CGRectMake(0, 0, image.size.width, image.size.height);
    scrollView.contentSize = image.size;

    UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(handleTapGesture:)];
    tapGesture.numberOfTapsRequired = 2;
    [imageView addGestureRecognizer:tapGesture];
    [tapGesture release];

    NSLog(@"LOADED");

    [super viewDidLoad];
}

-(IBAction) handleTapGesture:(UIGestureRecognizer *) sender {
    CGPoint tapPoint = [sender locationInView:imageView];
    int tapX = (int) tapPoint.x;
    int tapY = (int) tapPoint.y;
    NSLog(@"TAPPED X:%d Y:%d", tapX, tapY);
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Hello" message:@"How are you?" delegate:nil cancelButtonTitle:@"I'm awesome." otherButtonTitles:nil];
    [alert show];
    [alert release];
}

我几天前刚刚开始使用iPhone开发.这个问题让我想起了我在javascript中处理的事件冒泡问题.有任何想法吗？

Answer 1

不确定究竟是什么原因,但UIAlertView以某种方式导致手势再次触发.解决方法是使用performSelector执行手势处理程序外部的显示:

-(void) handleTapGesture:(UIGestureRecognizer *) sender {
    CGPoint tapPoint = [sender locationInView:imageView];
    int tapX = (int) tapPoint.x;
    int tapY = (int) tapPoint.y;
    NSLog(@"TAPPED X:%d Y:%d", tapX, tapY);
    [self performSelector:@selector(showMessage) withObject:nil afterDelay:0.0];
}

- (void)showMessage
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Hello" message:@"How are you?" delegate:nil cancelButtonTitle:@"I'm awesome." otherButtonTitles:nil];
    [alert show];
    [alert release];
}

编辑:
手势识别器在手势中经历不同的状态(开始,更改等),并且每次状态更改时都会调用处理程序方法.因此,更好且可能正确的解决方案是检查处理程序顶部的手势识别器的状态属性:

-(void) handleTapGesture:(UIGestureRecognizer *) sender {
    if (sender.state != UIGestureRecognizerStateEnded)  // <---
        return;                                         // <---

    CGPoint tapPoint = [sender locationInView:imageView];
    int tapX = (int) tapPoint.x;
    int tapY = (int) tapPoint.y;
    NSLog(@"TAPPED X:%d Y:%d", tapX, tapY);

    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Hello" message:@"How are you?" delegate:nil cancelButtonTitle:@"I'm awesome." otherButtonTitles:nil];
    [alert show];
    [alert release];
}