iphone - UIGestureRecognizer 触发两次？

Question

我已经在 View Controller 的 viewDidLoad 上设置了 UITapGestureRecognizer，但不知何故，它会为单次点击触发两次选择器方法。

UITapGestureRecognizer *g = [[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(openInMapsApp:)] autorelease];
[self.mapView addGestureRecognizer:g];

我的方法:

-(void)openInMapsApp:(UIGestureRecognizer*)g {
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@""
                                                    message:@"This will open this location in the Maps application. Continue?"
                                                   delegate:self
                                          cancelButtonTitle:@"Cancel"
                                          otherButtonTitles:@"OK",nil];
[alertView show];
[alertView release];
}

Answer 1

手势识别器发送具有不同手势状态的 Action 。所以这不是一个错误。解决方法是:

 UITapGestureRecognizer *g = [[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(openInMapsApp:)] autorelease];
[self.mapView addGestureRecognizer:g];

<小时/>

-(void)openInMapsApp:(UIGestureRecognizer*)g {
if(g.state != UIGestureRecognizerStateRecognized)
    return;
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@""
                                                    message:@"This will open this location in the Maps application. Continue?"
                                                   delegate:self
                                          cancelButtonTitle:@"Cancel"
                                          otherButtonTitles:@"OK",nil];
[alertView show];
[alertView release];
}