使用UITapGestureRecognizer

Question

新的iPhone開發。我有一個視圖，它包含一個包含UIImageView的UIScrollView。我在圖像視圖中添加了一個（雙）輕擊手勢識別器，這會使警告框打開。出於某種原因，我確信我只是被推遲了，它打開了3次。

這裏是我的代碼：

- (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]; 
} 

我剛開始iPhone開發幾天前。這個問題讓我想起了我在javascript中處理過的事件冒泡問題。有任何想法嗎？

Answer 1

不確定究竟是什麼原因，但UIAlertView以某種方式導致手勢再次觸發。一種解決方法是使用performSelector執行手勢處理機外部的顯示：

-(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]; 
} 

編輯：
姿勢識別經歷不同的狀態中的手勢（開始，改變等），它調用處理程序方法每次狀態改變。因此，一個更好，可能是正確的解決方案是在處理器的頂部檢查手勢識別器的狀態屬性：

-(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]; 
}