C++ data didn't update in Qml
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Hello guys ,
I have a frontend Qml , i want to display some data .
What i do is i create a backend.cpp class#ifndef BACKEND_H #define BACKEND_H #include <QObject> #include <QQmlEngine> class Backend : public QObject { Q_OBJECT Q_PROPERTY(QString directiontext READ getdirectiontext WRITE setdirectiontext NOTIFY directiontextChanged) QML_ELEMENT public: explicit Backend(QObject *parent = nullptr); QString getdirectiontext() {return m_directiontext;} ;} } //Setter methode // void setdirectiontext(QString text); signals: void directiontextChanged(); private : QString m_directiontext; }; #endif // BACKEND_H```//Backend.cpp
#include"backend.h"
#include<QDebug>
Backend::Backend(QObject *parent ) :QObject(parent)
{
m_directiontext="test direct";void Backend::setdirectiontext(QString text)
{
qDebug("signal direction called");
if(m_directiontext == text)
return;
m_directiontext = text;
emit directiontextChanged();
}I used a quickwidget to display Qml file here is my MainwindowqmlRegisterType<Backend>("com.beckend", 1, 0, "Myback");
m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);
m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));```and my qmlfile
import com.beckend 1.0 Myback{ id:back } Label { id: label5 x: 879 y: 192 text: back.directiontext }I have another class for change , so i create a command.cpp class and this is my code .
Backend back; QString Mode= ui->modecommande->currentText(); // this is a combobox qDebug() << Mode << "this is Mode select commande" ; back.setdirectiontext(Mode);when the combobox value change the data should change in my qmlfile .
Currently , i couldn't do this .
Any help please
thank you@dziko147 said in C++ data didn't update in Qml:
when the combobox value change the data should change in my qmlfile .
Currently , i couldn't do this .This cannot work as it is.
Backend back; QString Mode= ui->modecommande->currentText(); // this is a combobox qDebug() << Mode << "this is Mode select commande" ; back.setdirectiontext(Mode);This will create a local variable
backupdatesm_directiontextand destroy the variable on function end.
Why should QML be aware about this?
import com.beckend 1.0 Myback{ id:back }Will create a QML component
back, there is no link with C++ side.
The right way is to create a global instance of
Backend, and register it into QML context.qmlRegisterType<Backend>("com.beckend", 1, 0, "Myback"); m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView); // supposing m_ui has a member `m_back` m_ui->quickWidget->rootContext()->setContextProperty("backend", &m_back); m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));```Use this reference in QML and then all changes on C++ will be available on QML side.
Label { id: label5 x: 879 y: 192 text: backend.directiontext } -
@KroMignon thanks for your reply .
I tried this solution and it doesn't work . :/@dziko147 said in C++ data didn't update in Qml:
I tried this solution and it doesn't work . :/
Did you change also change the update method?
QString Mode= ui->modecommande->currentText(); // this is a combobox qDebug() << Mode << "this is Mode select commande" ; ui->m_back.setdirectiontext(Mode); -
@dziko147 said in C++ data didn't update in Qml:
I tried this solution and it doesn't work . :/
Did you change also change the update method?
QString Mode= ui->modecommande->currentText(); // this is a combobox qDebug() << Mode << "this is Mode select commande" ; ui->m_back.setdirectiontext(Mode); -
@dziko147 said in C++ data didn't update in Qml:
@KroMignon No ,
Can you suggest a method ?I don't understand what you mean, please be more clear.
No what?- No you don't have change the update method?
- After changing the update method, the QML didn't be update?
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@KroMignon the update method is in another class .
So how can get this m_back :)
i am really new in Qt developpment .
So excuse meif my question is stupid :)@dziko147 said in C++ data didn't update in Qml:
the update method is in another class .
So how can get this m_back :)
i am really new in Qt developpment .
So excuse meif my question is stupid :)I don't want to hurt you, but this has nothing to do with Qt, this is C++ basic.
Do you have any knowledge about C++ programming?
Do you know what is a class?
Do you know what is a class method or member?Please take time to got basic knowledge about the programming language you want to use.
There are many C++ tutorials available, take one and do at least the first step to understand what you are doing.Basic C++ knowledge is mandatory if you want to program with Qt which is a C++ framework.
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@KroMignon ok i will :)
but can you provide a way to create this m_back instance :)@dziko147 said in C++ data didn't update in Qml:
but can you provide a way to create this m_back instance :)
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@KroMignon I know how to use class/object .
I know how to manipulate c++ .
But my problem is how can get this in my second classm_ui->quickWidget->rootContext()->setContextProperty("backend", &m_back); -
@dziko147 said in C++ data didn't update in Qml:
So my problem is how can i get the m_back in the commande.cpp
Again, this is C++ basic => variable scope and life-cycle:
