How can I freeze picture of camera with CameraX API in Android Studio?

Question

I'm learning CameraX API, and CameraXBasic is a office sample code.

CameraFragment.kt in CameraXBasic displays a real camera preview, I hope to add a Switch button to freeze current preview, by which the picture will not change even if I move mobile phone camera lens.

How can I do with CameraX API? Thanks!

CameraFragment.kt

private lateinit var viewFinder: TextureView

private fun bindCameraUseCases() {
    // Get screen metrics used to setup camera for full screen resolution
    val metrics = DisplayMetrics().also { viewFinder.display.getRealMetrics(it) }
    val screenAspectRatio = Rational(metrics.widthPixels, metrics.heightPixels)
    Log.d(TAG, "Screen metrics: ${metrics.widthPixels} x ${metrics.heightPixels}")

    // Set up the view finder use case to display camera preview
    val viewFinderConfig = PreviewConfig.Builder().apply {
        setLensFacing(lensFacing)
        // We request aspect ratio but no resolution to let CameraX optimize our use cases
        setTargetAspectRatio(screenAspectRatio)
        // Set initial target rotation, we will have to call this again if rotation changes
        // during the lifecycle of this use case
        setTargetRotation(viewFinder.display.rotation)
    }.build()

    // Use the auto-fit preview builder to automatically handle size and orientation changes
    preview = AutoFitPreviewBuilder.build(viewFinderConfig, viewFinder)

 ....

 CameraX.bindToLifecycle(
            viewLifecycleOwner, preview, imageCapture, imageAnalyzer)
}

Answer 1

Add a PreviewOutputUpdateListener to the Preview , you can then decide wether to update the TextureView :

Java:

preview.setOnPreviewOutputUpdateListener(
        previewOutput -> {
            if(!frozen){
               textureView.setSurfaceTexture(previewOutput.getSurfaceTexture());
            }
});

Kotlin:

preview.setOnPreviewOutputUpdateListener {
    previewOutput: Preview.PreviewOutput? ->
        if(!frozen)
        textureView.setSurfaceTexture(previewOutput.getSurfaceTexture());
}

From Preview Documentation :

The preview use case produces a SurfaceTexture which streams the camera input. It also provides additional information for a View to crop, scale, or rotate for proper display.

The image preview is streamed to this SurfaceTexture when the camera becomes active. The SurfaceTexture can be connected to a TextureView or a GLSurfaceView.

So Preview by itself does not render anything and just provides a Texture to be rendered, it is up to you to decide what to do with this Texture returned by previewOutput.getSurfaceTexture() .