当我们想给MKMapView添加拖动手势时，第1个想法多是这样：
- (void)viewDidLoad
{
//....
UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
[self.mapView addGestureRecognizer:panGesture];
}
- (void)handlePan:(UIPanGestureRecognizer*) recognizer
{
NSLog("handlePan");
}
运行程序，然后拖动地图，我们会发现，控制台并没有打印任何的“handlePan”，也就是说手势辨认处理函数handlePan历来没有被履行。后来在stackoverflow上找到了答案，正确的解决方法以下：
- (void)viewDidLoad
{
//......
UIPanGestureRecognizer *panGesture = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handlePan:)];
panGesture.delegate = self;
[self.mapView addGestureRecognizer:panGesture];
}
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
return YES;
}
- (void)handlePan:(UIPanGestureRecognizer*) recognizer
{
NSLog("handlePan");
}
对照1下前后两段程序，后1段程序对手势辨认的代理进行了赋值，并实现了shouldRecognizeSimultaneouslyWithGestureRecognizer代理方法。
分析1下第2段代码运行成功的缘由：MKMapView内部实现时，已添加了1个UIPanGestureRecognizer，而这里我们又添加了另外1个UIPanGestureRecognizer，也就是说同1个MKMapView有两个相同类型的手势辨认，但是运行时内部默许相同类型的手势辨认只有1个会得到处理，所以第1段代码始终没有输出handlePan。幸亏UIPanGestureRecognizerDelegate提供了gestureRecognizer:shouldRecognizeSimultaneouslyWithGestureRecognizer方法，该方法返回YES时，意味着所有相同类型的手势辨认都会得到处理。