我想在上面加一个按钮，我试过很多程序，但都没用，按钮没有在相机上显示，有人能指导我吗？我希望扫描仪屏幕如下所示：https://i.stack.imgur.com/q9akx.png
这是密码
java文件

public class ScanCodeActivity extends AppCompatActivity implements ZXingScannerView.ResultHandler {

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

}

    @Override
    public void handleResult(Result result) {
        MainActivity.codigoBusquedaManual_AutoCompleteTextView.setText((result.getText()));
        MainActivity.codigoBusquedaManual_String = MainActivity.codigoBusquedaManual_AutoCompleteTextView.getText().toString();

        onBackPressed();

    }

    @Override
    protected void onPause() {
        super.onPause();

        ScannerView.stopCamera();
    }

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

这里是xml文件

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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=".ScanCodeActivity">

</android.support.constraint.ConstraintLayout>