gestures-scale-gestures.kt

// Implementation details omitted. Check out full sample
class DrawingCanvas: View(context) {

    // When the user pinches the view, zoom in, when they reverse pinch the view, zoom out
    private val scaleGestureDetector = ScaleGestureDetector(context, object :
            ScaleGestureDetector.SimpleOnScaleGestureListener() {
        override fun onScale(detector: ScaleGestureDetector?): Boolean {
            detector?.let {
                scaleX *= detector.scaleFactor
                scaleY *= detector.scaleFactor
            }
            return true
        }
    })

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        // Handle the different types of actions
        when (event?.actionMasked) {
            // ...
        }
        
        // Let the scale gesture detector analyze the event. If a scale gesture is detected, `onScale()` is invoked
        scaleGestureDetector.onTouchEvent(event)
        
        invalidate()
        return true
    }
}