Change QML Label text from a C++ function - c++

Question

I have a Label in QML and I want to change its text value when I click on a button. I have tried many different ways to achieve this, but nothing seems to work properly. I have used QObject::setProperty() and it seems to work when I print the new text value with qDebug(), but it does not refresh on the GUI. What am I doing wrong?
main.cpp:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include <QSettings>
#include <QQuickStyle>
#include <QtQuickControls2>
#include <QQmlContext>
#include <QIcon>
#include "Controllers/Network/network.hpp"
#include "Controllers/NFC/nfc.hpp"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QIcon::setThemeName("gallery");
QQuickStyle::setStyle("Material");
// Property bindings:
qmlRegisterType<RFS::Communication::Network>("rfs.communication.network", 1, 0, "Network");
qmlRegisterType<RFS::Communication::NFC>("rfs.communication.nfc", 1, 0, "NFC");
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("availableStyles", QQuickStyle::availableStyles());
engine.load(QUrl("qrc:/main.qml"));
if (engine.rootObjects().isEmpty()) return -1;
return app.exec();
}
nfc.hpp:
#include <QObject>
#include <QtNfc/qnearfieldmanager.h>
#include <QtNfc/qnearfieldtarget.h>
namespace RFS::Communication
{
class NFC : public QObject
{
Q_OBJECT
public:
explicit NFC(QObject *parent = nullptr);
Q_INVOKABLE bool getStatus() { return pairingStatus; }
Q_INVOKABLE void changeTextValue();
private:
bool pairingStatus;
};
}
nfc.cpp:
#include <QtQuick>
#include <QQuickView>
#include "Controllers/NFC/nfc.hpp"
void RFS::Communication::NFC::changeTextValue()
{
QQuickView view;
view.setSource(QUrl("qrc:/Views/overview.qml"));
QObject *rootObject = view.rootObject();
QList<QObject*> list = rootObject->findChildren<QObject*>();
QObject *testLabel = rootObject->findChild<QObject*>("testLabel");
qDebug() << "Object" << testLabel->property("text"); // Successfully prints old value
testLabel->setProperty("text", "test1");
qDebug() << "Object" << testLabel->property("text"); // Successfully prints new value
QQmlProperty(testLabel, "text").write("test2");
qDebug() << "Object" << testLabel->property("text"); // Successfully prints new value
}
overview.qml:
import QtQuick 2.12
import QtQuick.Controls 2.12
import rfs.communication.nfc 1.0
Page {
id: page
NFC {
id: nfc
}
SwipeView {
id: swipeView
anchors.fill: parent
currentIndex: tabBar.currentIndex
Pane {
id: overviewTab
width: swipeView.width
height: swipeView.height
Button {
id: pairButton
text: qsTr("Pair new receiver")
onClicked: {
nfc.changeTextValue()
}
}
Label {
id: testLabel
objectName: "testLabel"
text: "hei" // I want to change this value
}
}
}
}
Is there any better way to achieve this? Thanks a lot in advance.

Answer 1

Anyone looking for a simple solution, I just came up with this trying to achieve changing label's text on c++ side by pressing a button in QML
Add to main.cpp:
Backend backend;
engine.rootContext()->setContextProperty("backend", &backend);
Create a new class (backend.h & backend.cpp)
In backend.h:
#ifndef CONTROLLERS_H
#define CONTROLLERS_H
#include <Qt>
#include <QObject>
#include <QCoreApplication>
#include <QWindow>
#include <QString>
class Backend : public QObject
{
Q_OBJECT
public:
explicit Backend(QObject *parent = nullptr);
public slots:
void setText();
QString getText();
};
#endif // CONTROLLERS_H
In backend.cpp:
#include "backend.h"
QString text = ""; // don't forget this
Backend::Backend(QObject *parent) : QObject(parent)
{
}
QString Backend::getText()
{
return text; //returns the text you set or didnt in setText()
}
void Backend::setText()
{
text = "text"; // or do anything you want with global QString text
}
In QML:
Label{
id: myLabel
}
Button{
id: myButton
onClicked:{
backend.setText()
myLabel.text = backend.getText()
}
}