C++ Calling a getter method when it is not ready - c++

Question

I'm working on a project and it works but it is really messy so I am trying to clean it up by moving things around.
Here is a short version of the class containing the getter method
Link::Link
{
jsonUrl = QUrl("www.example.json");
QNetworkAccessManager *nam = new QNetworkAccessManager(this);
connect(nam,SIGNAL(finished(QNetworkReply*)),this,SLOT(downloadFinished(QNetworkReply*)));
QNetworkRequest request(jsonUrl);
nam->get(request)
}
void Link::downloadFinished(QNetworkReply *reply)
{
jsonArray = reply->readAll();
jsonStuff();
}
void Link::jsonStuff()
{
//does a bunch of json stuff then gets a string
string = map["url"].toString();
}
QString Link::getString()
{
return string;
}
Here is a short version of the class that calls the getter in the constructor
Header
class Commands
{
private:
Link link;
}
Source inside the constructor
Commands::Commands()
{
addCommand("!test", link.getString());
}
The problem is when I try to do it like this, I think the Commands constructor runs first and the string from the Link class is not ready yet so the string that comes out of link.getString() is empty. Is there a way to wait until the Link class finishes doing it's stuff and fills up the string before calling link.getString() inside the constructor of Commands? Not sure if this matters but most of my code is written in Qt
I hope you guys can understand what I'm trying to ask. My terminology is really poor.
Edit: Added more to my Link class

Answer 1

When the constructor of Commands (in this case Commands()) is called firstly it creates all variables(they are unintialized) in Commands class. That being said link is created via Link(). What you might want to do is to use jsonStuff() in the Link() constructor (it creates all member variables as well as), NOTE THAT it creates variables in this case it creates string with base costructor - it creates empty string.) Try following to fill the string:
Link() {
jsonStuff(); // string will be set
}
Or you can initialize it via initialization section:
Link() : string("Text") { }
Also you might want to return reference to string from getString() function. Reference means it doesn't create additional copy and it returns string which is stored in Link, so you can change string in a function where getString() is called. Also if it is read only you should use const reference.

Answer 2

Is there a way to wait until the Link class finishes doing it's stuff and fills up the string before calling link.getString() inside the constructor of Commands?
Certainly. The Link class must be a QObject that emits a signal when it has changed its properties - presumably based on the replies it got to its network request.
class Link : public QObject {
Q_OBJECT
Q_PROPERTY(QString string READ string WRITE setString NOTIFY stringChanged)
QString m_string;
public:
void jsonStuff() {
...
connect(reply, &QNetworkReply::finished, this, [this]{
...
setString(map["url"].toString());
});
}
void setString(const QString &s) {
if (m_string == s) return;
m_string = s;
emit stringChanged(m_string);
}
QString string() const { return m_string; }
Q_SIGNAL void stringChanged(const QString &);
};
You can then add the command when the link is ready:
Commands::Commands()
{
connect(&link, &Link::stringChanged, this, [this](const QString &string){
if (!string.isEmpty()) addCommand("!test", string);
});
}