如果一個UIView關聯多個UIGestureRecognizer, 會發生一個奇怪的問題，如下面代碼

[cpp]
    UIPanGestureRecognizer *pang = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panned:)]; 
    [self.view addGestureRecognizer:pang]; 
     
    UISwipeGestureRecognizer *swip = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swip:)]; 
    [self.view addGestureRecognizer:swip]; 
- (void)swip:(UISwipeGestureRecognizer *)gesture { 
    NSLog(@"swip"); 
} 
 
- (void)panned:(UIPanGestureRecognizer *)gesture { 
    NSLog(@"pan"); 
} 

    UIPanGestureRecognizer *pang = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(panned:)];
    [self.view addGestureRecognizer:pang];
   
    UISwipeGestureRecognizer *swip = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(swip:)];
    [self.view addGestureRecognizer:swip];
- (void)swip:(UISwipeGestureRecognizer *)gesture {
    NSLog(@"swip");
}

- (void)panned:(UIPanGestureRecognizer *)gesture {
    NSLog(@"pan");
}
結果是看不到swip的手勢觸發。

原因是系統event傳遞是，當有一個相響了，event就不會傳遞下去了。

要想兩個gesturerecognizer都起作用，只需要加幾行代碼就可以了

[cpp]
swip.delegate = self; 

swip.delegate = self;
然後實現，返回YES,表示還要響應otherGestureRecognizer.

[cpp] 
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer { 
    return YES; 
} 

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}
這下就可以看到swip在consol中打印出來。