ios - 是否可以使用 KVO 来跟踪对 `MKMapView.camera.heading` 属性的更改？

Question

我正在尝试使用相机航向属性跟踪 map 方向的变化。

// Register for notifications of changes to camera
if let camera = self.mapView?.camera {
    self.camera = camera
    camera.addObserver(self, forKeyPath: "heading", options: NSKeyValueObservingOptions.new, context: &MapViewController.myContext)
}

...

override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if context == &MapViewController.myContext {
        if keyPath == "heading" {
            if let heading = change?[NSKeyValueChangeKey.newKey] as? CLLocationDirection {
                self.heading = heading
            }
        }
    } else {
        super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
    }
}

Answer 1

相机属性模式是复制，因此您观察的不是当前相机实例，而只是观察调用 getter 时复制的相机实例。您需要在 map View 上观察 @"camera.heading" 或 @"camera" 的关键路径，并希望在标题发生变化时在内部设置一个新的相机对象.