为什么UIView：animateWithDuration立即完成？ [英] Why does UIView:animateWithDuration complete immediately?

问题描述

我有一个 MKPointAnnotation 的子类，它具有在iOS 4上运行的以下方法：

I have a subclass of MKPointAnnotation with the following method which I run on iOS 4:

- (void)animate {
    [UIView
     animateWithDuration: 3.0
     delay:1.0
     options:UIViewAnimationOptionAllowUserInteraction
     animations:^{
         CLLocationCoordinate2D loc = 
             CLLocationCoordinate2DMake([self coordinate].latitude + 0.001,
                                        [self coordinate].longitude + 0.001);
         [self setCoordinate:loc];

     }
     completion:^(BOOL finished) {
         NSLog(@"Is completed");
     }];
}

通过单击 UIBarButtonItem 。

我希望看到我的注释在 MKMapView 上移动。但是，当我这样调用方法时，我所看到的只是注释在其最终的静止位置：

I expect to see the my annotation travel across a MKMapView. However all I see is the annotation in its final resting place when I call the method like this:

[mapView addAnnotation:myAnnotation];
[myAnnotation animate];
[myAnnotation release];

仅当我调用如下方法时，才会出现预期的动画：

The intended animation only occurs if I call the method like this:

[mapView addAnnotation:myAnnotation];
[myAnnotation performSelector:@selector(animate) withObject:nil afterDelay:0.5];
[myAnnotation release];

请注意，如果 afterDelay较小，则会出现意想不到的行为，例如< 0.1s。

Note that I get the unintended behavior if the 'afterDelay', is smaller e.g. < 0.1s.

为什么会出现这种情况？

Any ideas why this could be the case?

推荐答案

动画最终会作用在 MKAnnotationView 上，而不是作用在 MKAnnotation 上。在 MKMapView 中添加注释并不一定意味着很快就会添加相应的视图。

The animation ultimately acts on the MKAnnotationView, not the MKAnnotation. Adding an annotation to a MKMapView does not necessarily mean that the corresponding view will be added any time soon.

因此如果您尝试为MKAnnotation设置动画，然后将其相应的 MKAnnotationView 添加到 MKMapView ，则会出现疯狂的行为。

Therefore you get crazy behaviour if you attempt to animate a MKAnnotation before its corresponding MKAnnotationView has been added to the MKMapView.

解决方案是仅在知道MKAnnotation对应的MKAnnotationView已添加到MKView后对其进行动画处理。您可以通过使用 MKMapViewDelegate -（void）mapView：（MKMapView *）mapView didAddAnnotationViews：（NSArray *）views 触发动画。

The solution is to only animate a MKAnnotation once you know its corresponding MKAnnotationView has been added to MKView. You can know this by using MKMapViewDelegate - (void)mapView:(MKMapView *)mapView didAddAnnotationViews:(NSArray *)views to trigger your animation.

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