Calling a variable from C++ in QML

[KroMignon]

@mamoud To create the instance:

Mysystem mysystem(0,1); // x= 0, y =1

viewer.rootContext()->setContextProperty("thepnumber", &mysystem);

[J.Hilk]

@mamoud

https://www.learncpp.com/cpp-tutorial/85-constructors/

[mamoud]

@VRonin

thanks
do you mean like this:

Q_PROPERTY(QString pNumber READ pNumber_read WRITE pNumber_write NOTIFY pNumber_changed)

and adding this as well:

public: QVariant pNumber_read() const;
public slots: void pNumber_write(QString value);  // i am not sure about this
signals: void pNumber_changed();
private: QString m_pNumber;

[VRonin]

@mamoud

Q_PROPERTY(QString pNumber READ pNumber WRITE setPNumber NOTIFY pNumberChanged)

public:
const QString& pNumber() const {return m_pNumber;}
void setPNumber(const QString& val){
if(val==m_pNumber) return;
m_pNumber=val;
pNumberChanged(m_pNumber);
}
signals:
void pNumberChanged(const QString& pN);
private:
QString m_pNumber;

[J.Hilk]

Pro (QtCreator) tip:

write

Q_PROPERTY(QString pNumber READ pNumber WRITE setPNumber NOTIFY pNumberChanged)

right click on Q_PROPERTY
select Refactor
click on Generate Missing Q_Property Members

saves a lot of time

[mamoud]

Great thank you,

but i still have this problem, that i cannot read the value in QML when i write this:

console.log (thepnumber.pNumber)

it shows nothing

[J.Hilk]

@mamoud said in Calling a variable from C++ in QML:

Great thank you,

but i still have this problem, that i cannot read the value in QML when i write this:

console.log (thepnumber.pNumber)

it shows nothing

more context please, where exactly is this called?

---

//General solution
Connections{
target: thepnumber

onpNumberChanged: console.log(thepnumber.pNumber)
}

[mamoud]

I have a QML called PageInfo.qml

Rectangle {
    id: infopage

    function pageEnter() {
        console.log("The part is: " + thepnumber.pNumber)
    }

[J.Hilk]

@mamoud said in Calling a variable from C++ in QML:

pageEnter

and when you call pageEnter?

[mamoud]

Once i enter this page it will be called

[J.Hilk]

@mamoud
if you write

function pageEnter() {
console.log("Enter Function to get Number")
console.log("The part is: " + thepnumber.pNumber)
}

do you see any console logs?

[VRonin]

Did you set a value to m_pNumber? if you never assign anything to it than it's totally natural that the log shows an empty string.

[mamoud]

Yeah i see
Enter Function to get Number
and also i see
The part is:
but no value is shown for thepnumber.pNumber

[mamoud]

@VRonin

No but this m_pNumber should get values from a CAN signal (canalyzer) which is set in .cpp file