Issue with QNetworkAccessManager Singleton Injection - c++

Question

I'm writing a RSS Feed Reader in Qt. My approach is to save every Feed in an object of the class Feed. The download is handled inside the Feed class, therefore I need to make sure that every object of Feed can access the (one) NetworkAccessManager. To manage this (and to make sure the NetworkAccessManager has only one instance) I want to make a Singleton injection. The problem is, with my current code I get the following error message
...main.cpp:-1: Fehler: undefined reference to `NetworkMgr::qnam'
Following is the code of which I think it is the most relevant for the problem, if you need anything more let me know.
I try to get the pointer on the instance of the NetworkAccessManager directly inside the constructor of the Feed class and then safe it in a private variable.
#ifndef FEED_H
#define FEED_H
#include <QObject>
#include <QGuiApplication>
#include <QtQuick>
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QNetworkRequest>
#include <QPixmap>
#include <iostream>
#include <QDomDocument>
#include "NetworkMgr.h"
using namespace std;
class Feed : public QObject {
Q_OBJECT
Q_PROPERTY(QString name READ name WRITE setName NOTIFY nameChanged)
Q_PROPERTY(QString url READ url WRITE setUrl NOTIFY urlChanged)
Q_PROPERTY(int id READ id WRITE setId NOTIFY idChanged)
Q_PROPERTY(bool active READ active WRITE setActive NOTIFY activeChanged)
public:
Feed(QObject* parent = NULL) : QObject(parent){
m_nMgr = NetworkMgr::getInstance();
connect(m_nMgr, SIGNAL(finished(QNetworkReply*)), this, SLOT(parse(QNetworkReply*)));
m_active = false;
};
QString name();
void setName(QString);
QString url();
void setUrl(QString);
int id();
void setId(int);
bool active();
void setActive(bool);
public slots:
void get();
private:
QString m_name;
QString m_url;
int m_id;
bool m_active;
QNetworkAccessManager* m_nMgr;
private slots:
void parse(QNetworkReply* reply);
signals:
void nameChanged();
void urlChanged();
void idChanged();
void activeChanged();
};
#endif
This is my Singleton class:
#ifndef NETWORKMGR_H
#define NETWORKMGR_H
#include <QObject>
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QNetworkRequest>
class NetworkMgr : public QObject {
Q_OBJECT
NetworkMgr(QObject* parent = NULL) : QObject(parent){};
~NetworkMgr(){
delete qnam;
}
static QNetworkAccessManager* qnam;
public:
static QNetworkAccessManager* getInstance(){
if(qnam == NULL){
qnam = new QNetworkAccessManager();
}
return qnam;
}
NetworkMgr(NetworkMgr const& copy) = delete;
NetworkMgr& operator=(NetworkMgr const& copy) = delete;
};
//QNetworkAccessManager* NetworkMgr::qnam = NULL;
#endif
As you can see, I also tried to initialize qnam to nullpointer, but then I get the error:
...Feed.h:17: Fehler: multiple definition of NetworkMgr::qnam' debug/main.o: In function Feed::~Feed()':
...Feed.h:17: multiple definition of `NetworkMgr::qnam'
And this is how I tried to call it as a test from main.cpp:
Feed feed;
feed.setUrl("https://www.deskmodder.de/blog/feed/");
feed.get();
I tried getting the instance of NetworkAccessManager outside the constructor as well, but the error stays the same.
I would really appreciate it, if anybody here has an idea what I could try to get rid of this error.. Before I take a completely different approach, I'd like to try it this way.
Thanks in advance to anyone contributing to fix my problem!