Trouble when using QNetworkReply in QT - c++

Question

I'm new in C++ also with QT, my current QT version is 5.5.1.
I have an issue when using connect with QNetworkReply and QNetworkAccessManager. When I try to assign a variable from another file to data fetched from API, it always calls the function first before connecting to the API so that the variable is always empty. Can you guys help me?
void NioshFunc::fetchDataFromAPI(){
QUrl url;
QUrlQuery querystr;
querystr.addQueryItem("$format","json");
url.setScheme("https");
url.setHost("example.com");
url.setPath("/aaaa/dataset");
url.setQuery(querystr);
QNetworkRequest request;
request.setUrl(url);
request.setRawHeader("KeyId", "xxx-xxx-xxx");
reply = manager->get(request);
connect(reply, &QNetworkReply::readyRead, this, &NioshFunc::readyRead);
connect(reply, &QNetworkReply::finished, this, &NioshFunc::finished);
}
void NioshFunc::readyRead(){
dataBuffer.append(reply->readAll());
}
void NioshFunc::finished(){
if(reply->error())
{
qDebug() << "ERROR!";
qDebug() << reply->errorString();
qDebug() << reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
qDebug() << reply->attribute(QNetworkRequest::HttpReasonPhraseAttribute).toString();
}else{
qDebug() << "SUCCESS";
qDebug() << reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt();
qDebug() << reply->attribute(QNetworkRequest::HttpReasonPhraseAttribute).toString();
nioshWPDataFromAPI = QJsonDocument::fromJson(dataBuffer);
qDebug() << nioshWPDataFromAPI;
dataBuffer.clear();
}
reply->deleteLater();
}
bool NioshFunc::parse(){
Globals *g = Globals::getHandle();
if (nioshWPDataFromAPI.isEmpty() || nioshWPDataFromAPI.isNull()) return false;
QVariantMap root = nioshWPDataFromAPI.toVariant().toMap();
if (root.isEmpty()) return false;
QVariantMap d = root["d"].toMap();
if (d.isEmpty()) return false;
QVariantList results = d["results"].toList();
if (results.isEmpty()) return false;
foreach (QVariant varResult, results)
{
QVariantMap result = varResult.toMap();
if (result.isEmpty()) return false;
g->struct_tableColumn.input.duration = result["Duration"].toString();
g->struct_tableColumn.input.id = result["Id"].toString();
if (id.isEmpty() || id.isNull()) return false;
g->struct_tableColumn.input.load_cumul_Limit = result["LoadCumulLimit"].toString();
g->struct_tableColumn.input.Notes = result["Notes"].toString();
qDebug() << g->struct_tableColumn.input.id << g->struct_tableColumn.input.duration << g->struct_tableColumn.input.load_cumul_Limit << g->struct_tableColumn.input.Notes; // "it is empty for all variable from globals file.
}
return true;
}
When I can function fetchDataFromAPI() and call function parse() in another file named globals, that is always called 2 these functions first before connecting to API, so that the variable named "nioshWPDataFromAPI" is always empty. But when I read nioshWPDataFromAPI in function finished(), it still has data, but only in function finished(). Could you guys help me? Sorry if my question is not too clear for you guys