iOS开发--MKMapView添加UIPanGestureRecognizer

当我们想给MKMapView添加拖动手势时，第一个想法可能是这样：

- (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”，也就是说手势识别处理函数handlePan从来没有被执行。后来在stackoverflow上找到了答案，正确的解决方法如下：

- (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");
}

对比一下前后两段程序，后一段程序对手势识别的代理进行了赋值，并实现了shouldRecognizeSimultaneouslyWithGestureRecognizer代理方法。

分析一下第二段代码运行成功的原因：MKMapView内部实现时，已经添加了一个UIPanGestureRecognizer，而这里我们又添加了另外一个UIPanGestureRecognizer，也就是说同一个MKMapView有两个相同类型的手势识别，然而运行时内部默认相同类型的手势识别只有一个会得到处理，所以第一段代码始终没有输出handlePan。幸好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识别都会得到处理。