当MKAnnotationView被拖动时如何获得连续的回调

Question

我有一个可以拖动的 MKAnnotationView，并且我已经实现了 didChangeDragState: 代理方法，在拖动开始和结束时会得到回调，但不是连续的。我想要在注释被拖动时跟踪其当前坐标，请帮我提供一些解决方案。谢谢。

- Kumaran

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尝试使用这个方法： - (void)mapView:(MKMapView *)mapView regionDidChangeAnimated:(BOOL)animated - Dhruv

Answer 1

据我所知，苹果没有提供一种方法让你这样做，但是你可以通过 KVO 实现（感谢 this answer）。

此外，你还需要手动确定注释视图的坐标，因为注释的坐标在进入 MKAnnotationViewDragStateEnding 后才会更新。

完整的解决方案如下：

// 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)
}

- Ziewvater

Answer 2

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;
  }

- Ashwin G

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当注释视图的拖动状态从一个状态更改为另一个状态时，才会调用此方法，它不会在视图被拖动时连续调用。仅在更改为“Dragging”状态时调用一次。此外，注释上的坐标仅在状态更改为“Ended”时更新，而在拖动时不会更新。 - Ziewvater