Auto-focus after X seconds and focus on tap in cameraX :

afterMeasuredExt.kt

inline fun View.afterMeasured(crossinline block: () -> Unit) {
    if (measuredWidth > 0 && measuredHeight > 0) {
        block()
    } else {
        viewTreeObserver.addOnGlobalLayoutListener(object : ViewTreeObserver.GlobalLayoutListener {
            override fun onGlobalLayout() {
                if (measuredWidth > 0 && measuredHeight > 0) {
                    viewTreeObserver.removeOnGlobalLayoutListener(this)
                    block()
                } 
            }
        })
    }
}

Autofocus.kt

 previewView.afterMeasured {
     val autoFocusPoint = SurfaceOrientedMeteringPointFactory(1f, 1f)
             .createPoint(.5f, .5f)
     try {
         val autoFocusAction = FocusMeteringAction.Builder(
             autoFocusPoint,
             FocusMeteringAction.FLAG_AF
         ).apply {
             //start auto-focusing after 2 seconds
             setAutoCancelDuration(2, TimeUnit.SECONDS)
         }.build()
         camera.cameraControl.startFocusAndMetering(autoFocusAction)
     } catch (e: CameraInfoUnavailableException) {
         Log.d("ERROR", "cannot access camera", e)
     }
 }

FocusOnTap.kt

previewView.afterMeasured {
     previewView.setOnTouchListener { _, event ->
         return@setOnTouchListener when (event.action) {
             MotionEvent.ACTION_DOWN -> {
                 true
             }
             MotionEvent.ACTION_UP -> {
                 val factory: MeteringPointFactory = SurfaceOrientedMeteringPointFactory(
                     previewView.width.toFloat(), previewView.height.toFloat()
                 )
                 val autoFocusPoint = factory.createPoint(event.x, event.y)
                 try {
                     camera.cameraControl.startFocusAndMetering(
                         FocusMeteringAction.Builder(
                             autoFocusPoint,
                             FocusMeteringAction.FLAG_AF
                         ).apply {
                             //focus only when the user tap the preview
                             disableAutoCancel()
                         }.build()
                     )
                 } catch (e: CameraInfoUnavailableException) {
                     Log.d("ERROR", "cannot access camera", e)
                 }
                 true
             }
             else -> false // Unhandled event.
         }
     }
 }