How to update a QML text with c++ - c++

Question

I have a small problem. Can someone show me how can I update a qml text from c++. I have an example using threads but I don't want to apply this method because I don't know how to set a
parameter in run() function.To fully understand me here is my code.In the main function when I start the thread I want to put my custom text or a string variable that has a text.
thread.h
#ifndef THREAD_H
#define THREAD_H
#include <QThread>
class Thread : public QThread
{
Q_OBJECT
public:
Thread(QObject *parent=nullptr);
~Thread() override;
Q_SLOT void stop();
Q_SIGNAL bool textChanged(const QString & text);
protected:
void run() override;
};
#endif // THREAD_H
thread.c
#include "thread.h"
#include <QDebug>
Thread::Thread(QObject *parent):
QThread(parent)
{
}
Thread::~Thread()
{
}
void Thread::stop()
{
requestInterruption();
wait();
}
void Thread::run() //here I want to specify a QString variable such that in main function to call the function with my text, and not specified the text from here
{
int i=0;
while(!isInterruptionRequested()){
QString text;
text = QString("I changed the text"); // I don't want to declare from here the text.
Q_EMIT textChanged(text);
QThread::msleep(20);
qDebug() <<i++;
}
}
main.cpp
...
Thread thread;
QQmlApplicationEngine engine;
QObject::connect(&app, &QGuiApplication::aboutToQuit, &thread, &Thread::stop);
thread.start();
engine.rootContext()->setContextProperty("thread", &thread);
engine.load(QUrl("qrc:/main.qml"));
thread.stop();
...
main.qml
.....
Text {
objectName: "myLabel"
id: txt
width: 200
height: 29
color: "#faf9f9"
text: qsTr("Text")
font.pixelSize: 12
}
Connections{
target: thread
onTextChanged: txt.text = text
}
.....

Answer 1

You can send data from C++ to qml using signals, like this:
//main.cpp
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
// Class init
YourClass yourObject;
// Embedding C++ Objects into QML with Context Properties
QQmlContext* ctx = engine.rootContext();
ctx->setContextProperty("yourObject", &yourObject);
return app.exec();
}
//main.qml
import QtQuick 2.6
Window {
id: mainWindow
Connections {
target: gapi
onSignalData: {
console.log("Data: " + data)
textToChange.text = "Changed to: " + data
}
}
Text {
id: textToChange
text: "beforeChange"
}
}
//yourClass.h
class YourClass : public QObject
{
signals:
// Signal from YourClass to QML
void signalData(QString data);
}
//yourClass.cpp
emit signalData("Hello QML"); // Signal from GAPI to QML
This page https://felgo.com/cross-platform-development/how-to-expose-a-qt-cpp-class-with-signals-and-slots-to-qml have a complete tutorial about "How to Expose a Qt C++ Class with Signals and Slots to QML"