How to run a C++ function when QML button is clicked? Using QQmlApplicationEngine

[Alaa Elrifaie]

myclass.h
@#ifndef MYCLASS_H
#define MYCLASS_H

#include <QDebug>
#include <QObject>

class MyClass : public QObject
{
public:
MyClass();

public slots:
void buttonClicked();
void buttonClicked(QString &in);
};

#endif // MYCLASS_H@

---

myclass.cpp
@#include "myclass.h"

MyClass::MyClass()
{
}

void MyClass::buttonClicked()
{
// Do Something
}

void MyClass::buttonClicked(QString &in)
{
qDebug() << in;
}@

---

main.cpp
@#include <QApplication>
#include <QQmlApplicationEngine>
#include <myclass.h>
#include <QQmlContext>

int main(int argc, char *argv[])
{
QApplication app(argc, argv);

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));

MyClass myClass;  // A class containing my functions

// Trying to "SetContextProperty" as I saw people do it to achieve C++/QML connection
QQmlContext *context = new QQmlContext(engine.rootContext());
context->setContextProperty("_myClass", &myClass);

return app.exec();

}@

............
I want to use a function in myClass class which takes a QString parameter when a QML button is clicked ..
When I compile & run .. it all goes smoothly. But when I click on the button .. it shows this error in the debugger:
qrc:///main.qml:80: ReferenceError: _myClass is not defined
~> "Line 80 in my QML file":
@74: MouseArea {
75: id: mouseArea1
76: anchors.fill: parent
77: hoverEnabled: true;
78: onEntered: { rectangle1.border.width = 2 }
79: onExited: { rectangle1.border.width = 1 }
80: onClicked: _myClass.buttonClicked("Worked?")
81: }@

[andreyc]

Welcome to Qt DevNet!

I think you missed Q_OBJECT macro in MyClass declaration
@
class MyClass : public QObject
{
Q_OBJECT // <-- This one
public:
@

[Alaa Elrifaie]

[quote author="andreyc" date="1406088144"]Welcome to Qt DevNet!

I think you missed Q_OBJECT macro in MyClass declaration[/quote]

Hi andreyc,
Now myclass.h looks like this:
@#ifndef MYCLASS_H
#define MYCLASS_H

#include <QDebug>
#include <QObject>

class MyClass: public QObject
{
Q_OBJECT

public:
MyClass();

public slots:
void buttonClicked();
void buttonClicked(QString &in);
};

#endif // MYCLASS_H
@

But now my code wouldn't compile at all! it gives me this compile error:
@C:\Users\Dell\Documents\Workspace\ProjectOne\myclass.h:7: error: undefined reference to `vtable for MyClass'@

[andreyc]

Have you rebuild the whole project after you added Q_OBJECT ?

[Alaa Elrifaie]

[quote author="andreyc" date="1406130397"]Have you rebuild the whole project after you added Q_OBJECT ?[/quote]

Oh sorry, I feel like an idiot now.
I've rebuilt the whole project, and it runs perfectly.

But when I click on the button I get this in the debugger:
@qrc:///main.qml:80: ReferenceError: _myClass is not defined@
<~ Same main problem.

[andreyc]

It works for me.

• main.cpp
  @
  int main(int argc, char *argv[])
  {
  QApplication app(argc, argv);

  QQmlApplicationEngine engine;
  engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
  QQmlContext *item = engine.rootContext();
  MyClass myClass;
  item->setContextProperty("_myClass", &myClass);

  return app.exec();
  }
  @

• MyClass.h
  @
  class MyClass : public QObject
  {
  Q_OBJECT
  public:
  //explicit MyClass(QObject *parent = 0) : QObject(parent) {}
  MyClass() {}

  signals:

  public slots:
  void buttonClicked(QString in)
  {
  qDebug() << "buttonClicked" << in;
  }

};
@

• main.qml
  @
  import QtQuick 2.2
  import QtQuick.Controls 1.1

ApplicationWindow {
visible: true
width: 640
height: 480
title: qsTr("Hello World")

menuBar: MenuBar {
    Menu {
        title: qsTr("File")
        MenuItem {
            text: qsTr("Exit")
            onTriggered: Qt.quit();
        }
    }
}


Rectangle {
    id: rectangle1
    width: 100
    height: 100
    color: "red"
    border.color: "black"
    border.width: 5
    radius: 10
}

MouseArea {
    id: mouseArea1
    anchors.fill: parent
    hoverEnabled: true;
    onEntered: { rectangle1.border.width = 2 }
    onExited: { rectangle1.border.width = 1 }
    onClicked: _myClass.buttonClicked("Worked?")
}

}
@

[dheerendra]

If your problem is still not resolved, Can you try item->setContextProperty("_myClass", &myClass); before loading the QML ?

[Alaa Elrifaie]

Thanks guys, it's solved.

I just had to remove the first declaration of my slot:
myclass.h

@#ifndef MYCLASS_H
#define MYCLASS_H

#include <QDebug>
#include <QObject>

class MyClass : public QObject
{
public:
MyClass();

public slots:
//void buttonClicked(); <~ This had to be removed in order to make it work
void buttonClicked(QString &in);
};

#endif // MYCLASS_H
@