JetPack最新库的简单介绍

    private fun startCamera() {
        val cameraProviderFuture = ProcessCameraProvider.getInstance(this)

        cameraProviderFuture.addListener(Runnable {
            // Used to bind the lifecycle of cameras to the lifecycle owner
            val cameraProvider: ProcessCameraProvider = cameraProviderFuture.get()

            // Preview
            val preview = Preview.Builder()
                .build()
                .also {
                    it.setSurfaceProvider(mViewFinder.surfaceProvider)
                }

            imageCapture = ImageCapture.Builder().build()

            // Select back camera as a default
            val cameraSelector = CameraSelector.DEFAULT_BACK_CAMERA

            try {
                // Unbind use cases before rebinding
                cameraProvider.unbindAll()

                // Bind use cases to camera
                cameraProvider.bindToLifecycle(
                    this, cameraSelector, preview, imageCapture)

            } catch(exc: Exception) {
                Log.e(TAG, "Use case binding failed", exc)
            }
    }

    private fun takePhoto() {
        // Get a stable reference of the modifiable image capture use case
        val imageCapture = imageCapture ?: return

        // Create time-stamped output file to hold the image
        val photoFile = File(
            outputDirectory,
            SimpleDateFormat(FILENAME_FORMAT, Locale.US
            ).format(System.currentTimeMillis()) + ".jpg")

        // Create output options object which contains file + metadata
        val outputOptions = ImageCapture.OutputFileOptions.Builder(photoFile).build()

        // Set up image capture listener, which is triggered after photo has
        // been taken
        imageCapture.takePicture(
            outputOptions, ContextCompat.getMainExecutor(this), object : ImageCapture.OnImageSavedCallback {
                override fun onError(exc: ImageCaptureException) {
                    Log.e(TAG, "Photo capture failed: ${exc.message}", exc)
                }

                override fun onImageSaved(output: ImageCapture.OutputFileResults) {
                    val savedUri = Uri.fromFile(photoFile)
                    val msg = "Photo capture succeeded: $savedUri"
                    Toast.makeText(baseContext, msg, Toast.LENGTH_SHORT).show()
                    Log.d(TAG, msg)
                }
            })
    }