//app.build lib
implementation 'me.dm7.barcodescanner:zxing:1.9.8'
//main clan for ui
package com.itclanbd.qr_code_reader;

import android.content.Intent;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    TextView resultview;
    Button capture;
    static String result_String="Scane is not complete";
    int REQUEST_CODE_FOR_QR = 1;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        resultview=(TextView)findViewById(R.id.result_show);
        capture=(Button)findViewById(R.id.cam_qr);
        capture.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                Intent intent = new Intent(getApplicationContext(), Result_activity.class);
                startActivityForResult(intent, REQUEST_CODE_FOR_QR);
            }
        });
    }
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data){
        if(requestCode == REQUEST_CODE_FOR_QR && resultCode == RESULT_OK && data!= null){
            result_String=data.getStringExtra(result_String);
            resultview.setText(result_String);
        }

    }
}

//qr class
package com.itclanbd.qr_code_reader;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;

import com.google.zxing.Result;

import me.dm7.barcodescanner.zxing.ZXingScannerView;

public class Result_activity extends AppCompatActivity implements ZXingScannerView.ResultHandler{

    private ZXingScannerView mScannerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        mScannerView = new ZXingScannerView(this);   // Programmatically initialize the scanner view
        setContentView(mScannerView);
    }
    @Override
    public void onResume() {
        super.onResume();
        mScannerView.setResultHandler(this); // Register ourselves as a handler for scan results.
        mScannerView.startCamera();          // Start camera on resume
    }

    @Override
    public void onPause() {
        super.onPause();
        mScannerView.stopCamera();           // Stop camera on pause
    }

    @Override
    public void handleResult(Result rawResult) {
        // Do something with the result here

        Intent resultIntent = new Intent();
        resultIntent.putExtra(MainActivity.result_String,rawResult.getText());
        setResult(RESULT_OK, resultIntent);
        finish();
        Toast.makeText(this, rawResult.getText(), Toast.LENGTH_LONG).show();
        Log.v("Text", rawResult.getText()); // Prints scan results
        Log.v("Barcode", rawResult.getBarcodeFormat().toString()); // Prints the scan format (qrcode, pdf417 etc.)

        // If you would like to resume scanning, call this method below:
        //mScannerView.resumeCameraPreview(this);
        //resultview.setText(rawResult.getText());
        //mScannerView.resumeCameraPreview(MainActivity.this);
    }

}