How to auto-focus with Android CameraX

Just point out, to get the "Tap to focus" working with PreviewView, you need to use DisplayOrientedMeteringPointFactory. Otherwise you'll get messed up coordinates.

val factory = DisplayOrientedMeteringPointFactory(activity.display, camera.cameraInfo, previewView.width.toFloat(), previewView.height.toFloat())

For the rest use the MatPag's answer.

There is an issue with some android devices where the camera's aren't auto-focusing with CameraX. The CameraX team is aware of it and are tracking it with an internal ticket and hopefully will have a fix soon.

With the current CameraX 1.0.0, you can proceed in this 2 ways:

1. Auto-focus every X seconds:

    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)
        }
    }
   

2. Focus on-tap:

    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.
            }
        }
    }
   

afterMeasured extension function is a simple utility: (thanks ch271828n for improving it)

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()
                } 
            }
        })
    }
}

A Camera object can be obtained with

val camera = cameraProvider.bindToLifecycle(
    this@Activity, cameraSelector, previewView //this is a PreviewView
)