Android-BAR|QR-Code-Scanner.kt

class MainActivity : AppCompatActivity() {

    private lateinit var surfaceView: SurfaceView
    private lateinit var barCodeDetector: BarcodeDetector
    private lateinit var cameraSource: CameraSource
    private val REQUST_CAMERA_PERMISSION = 123

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    override fun onStart() {
        super.onStart()
        initBarCodeDetectorAndCameraSources()
    }

    private fun initBarCodeDetectorAndCameraSources() {
        // Getting Surface View from Layout...
        surfaceView = findViewById(R.id.surfaceView)

        // Building Bar/QR Code Detector
        barCodeDetector = BarcodeDetector.Builder(this)
            .setBarcodeFormats(Barcode.ALL_FORMATS)
            .build()

        // Building Camera source for scanning BAR?QR Code
        cameraSource = CameraSource.Builder(this, barCodeDetector)
            .setRequestedPreviewSize(1920, 1080) // 640, 480 || 1024, 768 || 1920, 1080
            .setAutoFocusEnabled(true) // Obvious we should make auto focus enabled
            .setRequestedFps(25f)
            .build()

        // Reading BAR/QR Code data
        barCodeDetector.setProcessor(object : Detector.Processor<Barcode> {
            override fun release() {
                /** This method will call when we will release the barCodeDetector. And We must release the
                 barCodeDetector to prevent memory leaks */
            }
            override fun receiveDetections(detections: Detector.Detections<Barcode>?) {
                val barCodes = detections?.detectedItems
                barCodes?.let {
                    if (it.size() > 0) {
                        surfaceView.post {
                            showToast(it.valueAt(0).displayValue)
                            cameraSource.stop()
                        }
                    }
                }
            }
        })

        // Opening Camera When Surface is Created
        surfaceView.holder.addCallback(object : SurfaceHolder.Callback {

            override fun surfaceChanged(holder: SurfaceHolder?, format: Int, width: Int, height: Int) {}

            override fun surfaceDestroyed(holder: SurfaceHolder?) {
                cameraSource.stop()
            }

            override fun surfaceCreated(holder: SurfaceHolder?) {
                // Checking Camera Permission before starting camera for scanning
                try {
                    if (ContextCompat.checkSelfPermission(
                            this@MainActivity,
                            Manifest.permission.CAMERA
                        ) == PackageManager.PERMISSION_GRANTED
                    ) {
                        cameraSource.start(holder)
                    } else {
                        // Requesting Camera Permission if Permission is Missing
                        ActivityCompat.requestPermissions(this@MainActivity, arrayOf(Manifest.permission.CAMERA), REQUST_CAMERA_PERMISSION)
                    }
                } catch (e: IOException) {
                }
            }
        })
    }


    // Handing Camera Permission for Scanning BAR/QR Code...
    @SuppressLint("MissingPermission")
    override fun onRequestPermissionsResult(requestCode: Int, permissions: Array<out String>, grantResults: IntArray) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults)
        if (requestCode == REQUST_CAMERA_PERMISSION) {
            if (grantResults.isNotEmpty() && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                cameraSource.start(surfaceView.holder)
            } else showToast("Sorry, Scanner won't work without Camera Permission.")
        }
    }

    override fun onStop() {
        super.onStop()
        // Releasing detector and Camera Source to prevent memory leaks
        barCodeDetector.release()
        cameraSource.stop()
        cameraSource.release()
    }
}