Git Link: https://github.com/ismithpasha/QRCodeScanner

Code MainActivity.java:

package apps.scanner.qrscanner;

import android.*;
import android.Manifest;
import android.content.Context;
import android.content.pm.PackageManager;
import android.os.Vibrator;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.SparseArray;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
import android.widget.TextView;

import com.google.android.gms.vision.CameraSource;
import com.google.android.gms.vision.Detector;
import com.google.android.gms.vision.barcode.Barcode;
import com.google.android.gms.vision.barcode.BarcodeDetector;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    SurfaceView cameraPreview;
    TextView txtResult;
    BarcodeDetector barcodeDetector;
    CameraSource cameraSource;
    final int RequestCameraPermissionID = 1001;


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        switch (requestCode) {
            case RequestCameraPermissionID: {
                if (grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                         return;
                    }
                    try {
                        cameraSource.start(cameraPreview.getHolder());
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
           }
           break;
       }
    }

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

        cameraPreview = (SurfaceView) findViewById(R.id.cameraPreview);
        txtResult = (TextView) findViewById(R.id.txtResult);

        barcodeDetector = new BarcodeDetector.Builder(this)
                .setBarcodeFormats(Barcode.QR_CODE)
                .build();
        cameraSource = new CameraSource
                .Builder(this, barcodeDetector)
             //   .setRequestedPreviewSize(640, 480)
                .build();
        //Add Event
        cameraPreview.getHolder().addCallback(new SurfaceHolder.Callback() {
            @Override
            public void surfaceCreated(SurfaceHolder surfaceHolder) {
                if (ActivityCompat.checkSelfPermission(getApplicationContext(), Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                    //Request permission
                    ActivityCompat.requestPermissions(MainActivity.this,
                            new String[]{Manifest.permission.CAMERA},RequestCameraPermissionID);
                    return;
                }
                try {
                    cameraSource.start(cameraPreview.getHolder());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

            }

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

            }
        });

        barcodeDetector.setProcessor(new Detector.Processor<Barcode>() {
            @Override
            public void release() {

            }

            @Override
            public void receiveDetections(Detector.Detections<Barcode> detections) {
                final SparseArray<Barcode> qrcodes = detections.getDetectedItems();
                if(qrcodes.size() != 0)
                {
                    txtResult.post(new Runnable() {
                        @Override
                        public void run() {
                            //Create vibrate
                            Vibrator vibrator = (Vibrator)getApplicationContext().getSystemService(Context.VIBRATOR_SERVICE);
                            vibrator.vibrate(1000);
                            txtResult.setText(qrcodes.valueAt(0).displayValue);
                        }
                    });
                }
            }
        });
    }
}

Code activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:orientation="vertical"
    android:layout_height="match_parent"
    tools:context="apps.scanner.qrscanner.MainActivity">

    <SurfaceView
        android:id="@+id/cameraPreview"
        android:layout_width="match_parent"
        android:layout_height="0dip"
        android:layout_weight="3"/>

    <TextView
        android:gravity="center_horizontal"
        android:textSize="20sp"
        android:id="@+id/txtResult"
        android:layout_marginTop="20dp"
        android:text="Scan"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="3"/>

</LinearLayout>