camerax-previewview-pinch-to-zoom.kt

// Create a listener with a callback invoked when a gesture event has occurred
val listener = object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
    override fun onScale(detector: ScaleGestureDetector): Boolean {
        // Get the current camera zoom ratio
        val currentZoomRatio: Float = cameraInfo.zoomRatio.value ?: 1F
      
        // Get by how much the scale has changed due to the user's pinch gesture
        val delta = detector.scaleFactor
      
        // Update the camera's zoom ratio
        cameraControl.setZoomRatio(currentZoomRatio * delta)
        return true
    }
}

// Attach PreviewView's touch events listener to the scale gesture listener
val scaleGestureDetector = ScaleGestureDetector(context, listener)

// Pass touch events from PreviewView to the scale gesture listener 
previewView.setOnTouchListener { _, event ->
    scaleGestureDetector.onTouchEvent(event)
    return@setOnTouchListener true
}