How QR Code Scanner Work in Android Studio

In this article, we will read How QR Code Scanner Work in Android Studio . QR code stands for quick response code. It is 2 dimension bar code.QR code may store some data and this data can read by a Camera.

To generate your own QR Code you can go to th is link.

Let’s start code

build.gradle

For the Camera and bar code Detector we will use the following dependency

implementation  'com.google.android.gms:play-services-vision:20.1.3'

1	implementation 'com.google.android.gms:play-services-vision:20.1.3'

MainActivity

In MainActivity we create a button and when you click on that button you will be redirected to Scanner Acitivity.

    public class MainActivity extends AppCompatActivity {
        Button btnScanBarcode;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btnScanBarcode = findViewById(R.id.btnScanBarcode);
        btnScanBarcode.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this, ScanBarCodeActivity.class));
            }
        });
    }
}

public class MainActivity extends AppCompatActivity {

Button btnScanBarcode;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

btnScanBarcode = findViewById(R.id.btnScanBarcode);

btnScanBarcode.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View view) {

startActivity(new Intent(MainActivity.this, ScanBarCodeActivity.class));

}

});

}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    
    <Button
        android:id="@+id/btnScanBarcode"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="44dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:text="@string/scan_barcode"
    />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

tools:context=".MainActivity">

<Button

android:id="@+id/btnScanBarcode"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="44dp"

android:layout_marginEnd="8dp"

android:layout_marginStart="8dp"

android:layout_alignParentBottom="true"

android:layout_centerHorizontal="true"

android:text="@string/scan_barcode"

</RelativeLayout>

when you click on the button you will be redirected to ScanBarCodeActivity.

ScanBarCodeActivity

In initViews() method we parse intent data that is scanned from the scanner and on the resume method, we initialized initialiseDetectorsAndSources(). When we detect any code then reciveDetection() method will be called and intent data will be displayed.

  public class ScanBarCodeActivity extends AppCompatActivity {

    SurfaceView surfaceView;
    TextView txtBarcodeValue;
    private BarcodeDetector barcodeDetector;
    private CameraSource cameraSource;
    private static final int REQUEST_CAMERA_PERMISSION = 201;
    Button btnAction;
    String intentData = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scan_bar_code);
        initViews();
    }

    private void initViews() {
        txtBarcodeValue = findViewById(R.id.txtBarcodeValue);
        surfaceView = findViewById(R.id.surfaceView);
        btnAction = findViewById(R.id.btnAction);
        btnAction.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (intentData.length() > 0) {
                    startActivity(new Intent(Intent.ACTION_VIEW , Uri.parse(intentData)));
                }
            }
        });
    }

    private void initialiseDetectorsAndSources() {

        Toast.makeText(getApplicationContext() , "Barcode scanner started" , Toast.LENGTH_SHORT).show();
        barcodeDetector = new BarcodeDetector.Builder(this)
                .setBarcodeFormats(Barcode.ALL_FORMATS)
                .build();

        cameraSource = new CameraSource.Builder(this , barcodeDetector)
                .setRequestedPreviewSize(1920 , 1080)
                .setAutoFocusEnabled(true) //you should add this feature
                .build();

        surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder holder) {
                try {
                    if (ActivityCompat.checkSelfPermission(ScanBarCodeActivity.this , Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {
                        cameraSource.start(surfaceView.getHolder());
                    } else {
                        ActivityCompat.requestPermissions(ScanBarCodeActivity.this , new
                                String[]{Manifest.permission.CAMERA} , REQUEST_CAMERA_PERMISSION);
                    }

                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void surfaceChanged(SurfaceHolder holder , int format , int width , int height) {
            }

            @Override
            public void surfaceDestroyed(SurfaceHolder holder) {
                cameraSource.stop();
            }
        });


        barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
            @Override
            public void release() {
                Toast.makeText(getApplicationContext() , "To prevent memory leaks barcode scanner has been stopped" , Toast.LENGTH_SHORT).show();
            }

            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> barcodes = detections.getDetectedItems();
                if (barcodes.size() != 0) {
                    txtBarcodeValue.post(new Runnable() {
                        @Override
                        public void run() {
                            btnAction.setText("LAUNCH URL");
                            intentData = barcodes.valueAt(0).displayValue;
                            txtBarcodeValue.setText(intentData);
                        }
                    });
                }
            }
        });
    }


    @Override
    protected void onPause() {
        super.onPause();
        cameraSource.release();
    }

    @Override
    protected void onResume() {
        super.onResume();
        initialiseDetectorsAndSources();
    }
}

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public class ScanBarCodeActivity extends AppCompatActivity {

SurfaceView surfaceView;

TextView txtBarcodeValue;

private BarcodeDetector barcodeDetector;

private CameraSource cameraSource;

private static final int REQUEST_CAMERA_PERMISSION = 201;

Button btnAction;

String intentData = "";

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_scan_bar_code);

initViews();

}

private void initViews() {

txtBarcodeValue = findViewById(R.id.txtBarcodeValue);

surfaceView = findViewById(R.id.surfaceView);

btnAction = findViewById(R.id.btnAction);

btnAction.setOnClickListener(new View.OnClickListener() {

@Override

public void onClick(View v) {

if (intentData.length() > 0) {

startActivity(new Intent(Intent.ACTION_VIEW , Uri.parse(intentData)));

}

});

}

private void initialiseDetectorsAndSources() {

Toast.makeText(getApplicationContext() , "Barcode scanner started" , Toast.LENGTH_SHORT).show();

barcodeDetector = new BarcodeDetector.Builder(this)

.setBarcodeFormats(Barcode.ALL_FORMATS)

.build();

cameraSource = new CameraSource.Builder(this , barcodeDetector)

.setRequestedPreviewSize(1920 , 1080)

.setAutoFocusEnabled(true) //you should add this feature

.build();

surfaceView.getHolder().addCallback(new SurfaceHolder.Callback() {

@Override

public void surfaceCreated(SurfaceHolder holder) {

try {

if (ActivityCompat.checkSelfPermission(ScanBarCodeActivity.this , Manifest.permission.CAMERA) == PackageManager.PERMISSION_GRANTED) {

cameraSource.start(surfaceView.getHolder());

} else {

ActivityCompat.requestPermissions(ScanBarCodeActivity.this , new

String[]{Manifest.permission.CAMERA} , REQUEST_CAMERA_PERMISSION);

}

} catch (IOException e) {

e.printStackTrace();

}

@Override

public void surfaceChanged(SurfaceHolder holder , int format , int width , int height) {

}

@Override

public void surfaceDestroyed(SurfaceHolder holder) {

cameraSource.stop();

}

});

barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {

@Override

public void release() {

Toast.makeText(getApplicationContext() , "To prevent memory leaks barcode scanner has been stopped" , Toast.LENGTH_SHORT).show();

}

@Override

public void receiveDetections(Detector.Detections<Barcode> detections) {

final SparseArray<Barcode> barcodes = detections.getDetectedItems();

if (barcodes.size() != 0) {

txtBarcodeValue.post(new Runnable() {

@Override

public void run() {

btnAction.setText("LAUNCH URL");

intentData = barcodes.valueAt(0).displayValue;

txtBarcodeValue.setText(intentData);

}

});

}

});

}

@Override

protected void onPause() {

super.onPause();

cameraSource.release();

}

@Override

protected void onResume() {

super.onResume();

initialiseDetectorsAndSources();

}

activity_scan_bar_code

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp">

    <SurfaceView
        android:id="@+id/surfaceView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_above="@+id/btnAction"
        android:layout_alignParentLeft="true"
        android:layout_alignParentStart="true"
        android:layout_centerVertical="true" />

    <TextView
        android:id="@+id/txtBarcodeValue"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_marginLeft="10dp"
        android:layout_marginStart="10dp"
        android:text="No Barcode Detected"
        android:textColor="@android:color/white"
        android:textSize="20sp" />


    <Button
        android:id="@+id/btnAction"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:text="MOVE TO QR CODE" />
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:padding="10dp">

<SurfaceView

android:id="@+id/surfaceView"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:layout_above="@+id/btnAction"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_centerVertical="true" />

<TextView

android:id="@+id/txtBarcodeValue"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentTop="true"

android:layout_marginLeft="10dp"

android:layout_marginStart="10dp"

android:text="No Barcode Detected"

android:textColor="@android:color/white"

android:textSize="20sp" />

<Button

android:id="@+id/btnAction"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:text="MOVE TO QR CODE" />

</RelativeLayout>

Please check attached screenshot.In First Screenshot you can see Main Layout and when you click on scan button then camera will be open.After scanning QR code bar code detector will detect code and then you can see that code or search the link.