QML and C++ connect to signal - c++

Question

I want to connect QML Signals to c++ functions. I do not really understand how I can get the right item. Right now I try it in the following way, which is not working (Also, would there be easier ways?), here is the code I tried:
main.cpp:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "include/myclass.h"
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
QQmlComponent component(&engine, "qrc:/Page1.qml");
QObject *item = component.create();
MyClass myClass;
QObject::connect(item, SIGNAL(testSignal()),&myClass,SLOT(cppSlot()));
return app.exec();
}
main.qml:
import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0
ApplicationWindow {
visible: true
width: 800
height: 460
Page1 {
id: page1
visible: true
}
}
Page1.qml:
import QtQuick 2.7
import QtQuick.Window 2.2
Item {
width: 800
height: 460
signal testSignal()
CustomButton {
id: cppSignalButton
x: 14
y: 55
buttonText: "Test CPP Signal"
onButtonClicked: {
testSignal();
}
}
}
CustomButton.qml:
import QtQuick 2.7
import QtQuick.Window 2.2
Rectangle {
id: root
width: 200
height: 50
color: "#000000"
border.color: "#FFFFFF"
property string buttonText
signal buttonClicked()
MouseArea {
id: mouseArea
anchors.fill: parent
onClicked:{
root.buttonClicked();
}
}
Text {
id: text1
x: 105
y: 31
color: "#ffffff"
text: buttonText
anchors.verticalCenter: parent.verticalCenter
anchors.horizontalCenter: parent.horizontalCenter
font.pixelSize: 20
}
}
and myclass.cpp:
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <iostream>
#include <fstream>
#include <QQuickItem>
#include <QQuickView>
class MyClass : public QObject
{
Q_OBJECT
public:
MyClass(){
};
public slots:
void cppSlot() {
std::ofstream textfile;
textfile.open("test.txt");
textfile << "Signal worked" << std::endl;
textfile.close();
qInfo( "Called the C++ slot" );
}
};

Answer 1

First you should read this article: Integrating QML and C++
You can invoke your MyClass object method from qml in the following way:
//main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "include/myclass.h"
int main(int argc, char *argv[])
{
QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
MyClass myClass;
engine.rootContext()->setContextProperty("myClass", &myClass);
engine.load(QUrl(QLatin1String("qrc:/main.qml")));
return app.exec();
}
//Page1.qml
import QtQuick 2.7
import QtQuick.Window 2.2
Item {
width: 800
height: 460
signal testSignal()
CustomButton {
id: cppSignalButton
x: 14
y: 55
buttonText: "Test CPP Signal"
onButtonClicked: {
myClass.cppSlot(); //now you can use the context property to invoke your slot
}
}
}