Handling signals across several QMLs - c++

Question

I just began learning about Qt programming and found myself struggling with the signals and slot mechanism while making a simple test application.
I have two QML files: main.qml and grocery.qml.
I have a header file that manages the signals and slots of the application:
applicationamanger.h
#ifndef APPLICATIONMANAGER_H
#define APPLICATIONMANAGER_H
#include <QObject>
#include <QDebug>
class ApplicationManager : public QObject
{
Q_OBJECT
public:
explicit ApplicationManager(QObject *parent = 0);
signals:
void newGroceryItem();
public slots:
void addGroceryItem();
};
#endif // APPLICATIONMANAGER_H
The user starts the application on main.qml and when pressing a button loads grocery.qml
On grocery.qml I have an image that can be clicked by the user and emits the signal newGroceryItem()
MouseArea {
id: okBtnClkd
anchors.fill: parent
Connections {
onClicked: {
newGroceryItem()
}
}
}
And the main application main.cpp connects the signals but says it can't find the signal newGroceryItem() as it doesn't belong to main.qml. So my question is, how can I establish the connection to the slot addGroceryItem() from the secondary qml file grocery.qml?
EDIT:
As requested here're the contents of main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQuickWindow>
#include <QQmlContext>
#include "applicationmanager.h"
int main(int argc, char *argv[]){
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
QObject *topLevel = engine.rootObjects().value(0);
QQuickWindow *window = qobject_cast<QQuickWindow *>(topLevel);
ApplicationManager applicationManager;
QObject::connect(window, SIGNAL(newGroceryItem()), &applicationManager, SLOT(addGroceryItem()));
return app.exec();
}
And the contents of grocery.qml
import QtQuick 2.5
import QtQuick.Controls 1.4
ApplicationWindow {
//Declaration of signals.
signal newGroceryItem()
width: 300
height: 400
visible: true
TextField {
id: product
x: 14
y: 111
width: 270
height: 22
}
Text {
id: text1
x: 14
y: 81
width: 124
height: 24
text: qsTr("Product")
font.pixelSize: 20
}
Image {
id: okBtn
x: 99
y: 290
width: 100
height: 100
source: "img/main/okBtn.png"
MouseArea {
id: okBtnClkd
anchors.fill: parent
Connections {
onClicked: {
newGroceryItem()
}
}
}
}
}

Answer 1

Any method of a QObject-derived type is accessible from QML code if it is:
a public method flagged with the Q_INVOKABLE macro
a method that is a public Qt SLOT
So there are two ways to access addGroceryItem(). The first one is to use Q_INVOKABLE macro as follows:
class ApplicationManager : public QObject
{
Q_OBJECT
public:
explicit ApplicationManager(QObject *parent = 0);
Q_INVOKABLE void addGroceryItem();
};
The second way is to use public slots as follows:
class ApplicationManager : public QObject
{
Q_OBJECT
public:
explicit ApplicationManager(QObject *parent = 0);
public slots:
void addGroceryItem();
};
If you are creating your class object in C++ then you should set the object as the context data for main.qml as follows:
int main(int argc, char *argv[]) {
QCoreApplication app(argc, argv);
QQmlEngine engine;
ApplicationManager app;
engine.rootContext()->setContextProperty("applicationManager", &app);
QQmlComponent component(&engine, QUrl::fromLocalFile("main.qml"));
component.create();
return app.exec();
}
Now you can access the ApplicationManager object created in main.cpp from main.qml as follows:
MouseArea {
id: okBtnClkd
anchors.fill: parent
onClicked: {
applicationManager.addGroceryItem();
}
}
For more information see here.