如何在CameraX接口中切换摄像头？

implementation 'androidx.camera:camera-camera2:1.0.0'
implementation 'androidx.camera:camera-lifecycle:1.0.0'
implementation 'androidx.camera:camera-view:1.0.0-alpha23'

<androidx.camera.view.PreviewView
    android:id="@+id/previewView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

private fun startCamera() {
    val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
    cameraProviderFuture.addListener(Runnable {
        val cameraProvider = cameraProviderFuture.get()
        bindPreview(cameraProvider)
    }, ContextCompat.getMainExecutor(this))
}

private fun bindPreview(cameraProvider: ProcessCameraProvider) {
    val preview = Preview.Builder()
        .build()
        .also {
            it.setSurfaceProvider(previewView.createSurfaceProvider())
        }

    val cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA

    try {
        cameraProvider.unbindAll()
        cameraProvider.bindToLifecycle(this, cameraSelector, preview)
    } catch (exc: Exception) {
        Log.e(TAG, "Error binding camera", exc)
    }
}

private fun switchCamera() {
    val cameraProviderFuture = ProcessCameraProvider.getInstance(this)
    cameraProviderFuture.addListener(Runnable {
        val cameraProvider = cameraProviderFuture.get()
        val cameraSelector = if (currentCameraSelector == CameraSelector.DEFAULT_BACK_CAMERA) {
            CameraSelector.DEFAULT_FRONT_CAMERA
        } else {
            CameraSelector.DEFAULT_BACK_CAMERA
        }
        bindPreview(cameraProvider, cameraSelector)
    }, ContextCompat.getMainExecutor(this))
}