我正在使用Zxing库应用程序创建QR扫描仪，编译成功，但QR扫描仪未显示该应用程序

Question

package com.example.qr;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import com.google.zxing.Result;

import me.dm7.barcodescanner.zxing.ZXingScannerView;

public class Main2Activity extends AppCompatActivity implements ZXingScannerView.ResultHandler {

    private ZXingScannerView scannerView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        scannerView = new ZXingScannerView(this);
        setContentView(scannerView);
    }

    @Override
    public void handleResult(Result result) {

        MainActivity.txtqrsearch.setText(result.getText());
        onBackPressed();


    }

    @Override
    protected void onResume() {
        super.onResume();
        scannerView.setResultHandler(this);
        scannerView.startCamera();
    }

    @Override
    protected void onPause() {
        super.onPause();
        scannerView.stopCamera();
    }
}