QByteArray helloWorld = "Hello World";

    QVariantList list;
    list << helloWorld;

    QJsonArray array = QJsonArray::fromVariantList(list);
    qDebug().noquote() << "Source" << helloWorld;
    qDebug().noquote() << "String" << array.first().toString();
    qDebug().noquote() << "ByteArray" << array.first().toVariant().toByteArray();