Scope issues with Qt Quick and C++ classes - c++

Question

I have a project that I am working on, that will hopefully result in C++ code with a QML UI as a console, communicating with other consoles and equipment.
My test setup is based on a RaspBerry Pi running UDP comms (works fine into a normal Qt application).
I have tried to port to Qt Quick, and use a simple QML UI, but if I declare the subclass early in my "main.cpp" it doesn't connect properly.
If I declare it in the main.cpp "main" function, then I have scope issues with the subclass functions that I want to use to transfer data.
Open to suggestions / critique......and I am 100% sure that there is a "proper" way of doing this, so if anyone wants to point me at it......I will be enraptured!
Qt version is Qt5.3.
import QtQuick 2.2
import QtQuick.Controls 1.1
Rectangle {
width: 440; height: 150
color: "orange"
Column {
anchors.fill: parent; spacing: 20
Text {
text: rootItem.theChange
font.pointSize: 12; anchors.horizontalCenter: parent.horizontalCenter
}
}
}
// signalgrab.h
#ifndef SIGNALGRAB_H
#define SIGNALGRAB_H
#include <QObject>
#include <QUdpSocket>
#include <QString>
class SignalGrab : public QObject
{
Q_OBJECT
public:
explicit SignalGrab(QObject *parent = 0);
int SendValue();
void setupUDP();
signals:
public slots:
void readyRead();
private:
QUdpSocket *socket;
QHostAddress groupAddress;
};
#endif // SIGNALGRAB_H
// signalgrab.cpp
#include "signalgrab.h"
int i3 = 0;
SignalGrab::SignalGrab(QObject *parent) :
QObject(parent)
{
// create a QUDP socket
socket = new QUdpSocket(this);
socket->bind(QHostAddress("0.0.0.0"), 45454);
connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
qDebug() << "Socket connected ok!";
}
void SignalGrab::readyRead()
{
// when data comes in
QByteArray buffer;
buffer.resize(socket->pendingDatagramSize());
QHostAddress sender;
quint16 senderPort;
socket->readDatagram(buffer.data(), buffer.size(),
&sender, &senderPort);
std::string s1 (buffer);
std::string s2 = s1.substr(26,sizeof(s1));
i3 = atoi(s2.data());
SendValue();
}
int SignalGrab::SendValue()
{
qDebug() << "sending i3 as: "<< i3;
return i3;
}
// main.cpp
#include <QtGui>
#include <QApplication>
#include <QQmlContext>
#include <QQuickView>
#include <QString>
#include "signalgrab.h"
int y=13;
// ///////////////////////////////////
//SignalGrab nc;
// ///////////////////////////////////
class Object : public QObject
{
Q_OBJECT
Q_PROPERTY(QString theChange READ getTheChange NOTIFY changeOfStatus)
public:
Object()
{
changeMe = false;
myTimer = new QTimer(this);
myTimer->start(5000);
connect(myTimer, SIGNAL(timeout()), this, SLOT(testSlot()));
}
QString getTheChange()
{
if (theValue == 0)
{
return "The Acid QML Test";
}
if (theValue == 1)
{
y = (fetchValue());
qDebug() << "New y!" << y;
return QString("Returning %1").arg(y);
}
return "nothing has happened yet";
}
int fetchValue()
{
// return (nc::SendValue());
return y;
}
Q_INVOKABLE void someFunction(int i)
{
if ( i == 0) {
theValue = 0;
}
if (i == 1) {
theValue = 1;
}
emit changeOfStatus(i);
}
signals:
void changeOfStatus(int i) ;
public slots:
void testSlot()
{
if (changeMe)
{
someFunction(0);
} else {
someFunction(1);
}
changeMe = !changeMe;
}
private:
bool changeMe;
int theValue;
QTimer *myTimer;
};
#include "main.moc"
int main(int argc, char** argv)
{
QApplication app(argc, argv);
Object myObj;
// //////////////////////////////
SignalGrab nc; //added
// //////////////////////////////
nc.SendValue();
QQuickView view;
view.rootContext()->setContextProperty("rootItem", (QObject *)&myObj);
view.setSource(QUrl::fromLocalFile("main.qml"));
view.show();
return app.exec();
}