如何在特定的图像旋转上触发事件？

Question

I'm using this code to align the myCompass -ImageView to the current device heading. (Rotate the image to point in North direction --> it's a compass )

func locationManager(_ manager: CLLocationManager, didUpdateHeading newHeading: CLHeading) {
    let Heading = newHeading.trueHeading.toRadians

    UIView.animate(withDuration: 0.5) {
        self.myCompass.transform = CGAffineTransform(rotationAngle: CGFloat(-Heading))
    }
}

This code is working quiet fine but as you can see I've added a small animation so that the rotation of the IMageView doesn't looks that ugly.

Problem: Now I want to fire an event if the myCompass -view is pointing exactly to the north pole .

if (Heading > -4 && Heading < 4) {
  event()
}

• --> Because of the animation I can not check the heading because it could take about 0.5 seconds till the needle exactly points to North.

• --> I can not check the heading & add a 0.5-delay because the heading could change within this 0.5 seconds again

---

SO to my question:

Is it possible to listen for some kind of specific rotation event of an ImageView?

Or is there some more elegant way to get a result like this?

Maybe something like this pseudo code:

myCompass.onOrientation(rotationAngleMin: 5, rotationAngleMax: -5, event) 
func event() {
  print("hurray")
}

Answer 1

You can try key-value observing on transform property of you image by:

myCompass.addObserver(self, forKeyPath: "transform", options: [.old, .new], context: nil)

and then observe it in the following method

override func addObserver(_ observer: NSObject, forKeyPath keyPath: String, options: NSKeyValueObservingOptions = [], context: UnsafeMutableRawPointer?) {
    if keyPath == "transform" {
        // Check your updates here

    }
}

Hope it works!!