objective-c - 拖动MKAnnotationView时如何获得连续回调

Question

我有MKAnnotationView哪个是可拖动的，并且我已经实现didChangeDragState:了委托方法，我在拖动开始和结束时获得回调，但不是连续的。我想跟踪注释的当前坐标，因为它被拖动，请帮助我一些解决方案。谢谢你。

Answer 1

坐标可以从 annotationview.coordinates 获得：

  -(void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view   
  didChangeDragState:(MKAnnotationViewDragState)newState fromOldState:
  (MKAnnotationViewDragState)oldState
  {
  CLLocationCoordinate2D currentCoordinates = view.annotation.coordinate;
  }

Answer 2

据我所知，没有 Apple 提供的方法供您执行此操作，但您可以通过 KVO 实现它（h/t to this answer）。

您还需要手动确定注解视图的坐标，因为注解的坐标在进入MKAnnotationViewDragStateEnding.

完整的解决方案如下所示：

// Somewhere in your code before the annotation view gets dragged, subscribe your observer object to changes in the annotation view's frame center
annotationView.addObserver(DELEGATE_OBJECT, forKeyPath: "center", options: NSKeyValueObservingOptions.New, context: nil)

// Then in the observer's code, fill out the KVO callback method
// Your observer will need to conform to the NSKeyValueObserving protocol -- all `NSObject`s already do
override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
    // Check that we're observing an annotation view. The `where` clause can be omitted if you're only observing changes in its frame, or don't care about extra calls
    if let annotationView = object as? MKAnnotationView where keyPath == "center" {
        // Defined below, `coordinateForAnnotationView` converts a CGPoint measured within a given MKMapView to the geographical coordinate represented in that location
        let newCoordinate = coordinateForAnnotationView(pin, inMapView: self.mapView)

        // Do stuff with `newCoordinate`
    }
}

func coordinateForAnnotationView(annotationView: MKAnnotationView, inMapView mapView: MKMapView) -> CLLocationCoordinate2D {
    // Most `MKAnnotationView`s will have a center offset, including `MKPinAnnotationView`
    let trueCenter = CGPoint(x: annotationView.center.x - annotationView.centerOffset.x,
        y: annotationView.center.y - annotationView.centerOffset.y)

    return mapView.convertPoint(trueCenter, toCoordinateFromView: mapView)
}