我的应用未运行旧库zxing

您应遵循Android的文档检查和请求权限。 https://developer.android.com/training/permissions/requesting

我已经修改了您的代码，这应该是一个有效的示例。

public class MainActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler {
    private ZXingScannerView mScannerView;
    private static final int MY_PERMISSIONS_REQUEST_CAMERA = 101;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.activity_main);
        // Programmatically initialize the scanner view
        mScannerView = new ZXingScannerView(this);
        setContentView(mScannerView);
    }

    @Override
    public void handleResult(Result rawResult) {
        // Do something with the result here
        Log.v("TAG", rawResult.getText()); // Prints scan results
        // Prints the scan format (qrcode, pdf417 etc.)
        Log.v("TAG", rawResult.getBarcodeFormat().toString());
        AlertDialog.Builder builder = new AlertDialog.Builder(this);
        builder.setTitle("Scan Result");
        builder.setMessage(rawResult.getText());
        AlertDialog alert1 = builder.create();
        alert1.show();

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

    @Override
    public void onResume() {
        super.onResume();
        // Register ourselves as a handler for scan results.
        mScannerView.setResultHandler(this);
        // Start camera on resume

        if (hasPermission(Manifest.permission.CAMERA)) {
            startCamera();
        }
    }

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

    private void startCamera() {
        mScannerView.startCamera();
    }

    private Boolean hasPermission(String permission) {
        if (ContextCompat.checkSelfPermission(this, permission) != PackageManager.PERMISSION_GRANTED) {
            // you need to request the permission
            Log.d("TAG", "User hasn't granted permission.");

            // No explanation needed for camera. request the permission
            ActivityCompat.requestPermissions(this,
                    new String[]{permission},
                    MY_PERMISSIONS_REQUEST_CAMERA);
        }
        else {
            Log.d("TAG",  "User already granted permission.");
            return true;
        }
        return false;
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        switch (requestCode) {
            case MY_PERMISSIONS_REQUEST_CAMERA:
                // If request is cancelled, the result arrays are empty.
                if (grantResults.length > 0
                        && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                    startCamera();
                } else {
                    Log.d("TAG", "Permission denied by user...");
                }
                break;
        }
    }
}