How to emit signals from source to replica using QT Remote Objects

Question

How to emit a signal from source c++ file and capture it using connections in replica file. I have declared the signal and the slot emitting the signal in rep file.Trying to catch the signal using Connections: and target as replica object.I have setcontext the replicaobject in my client qt engine. //.rep file class test { SLOT(test()); SIGNAL(testsignal()); }

//Interface.cpp file in source side
void Interface::test()
{
    Q_EMIT testsignal();
}

//main.qml in the client side Connections { target: Interfacereplica onTestsignal: { console.log("Alert!!!"); }

score 2 · Answer 1 · answered Jan 17 '22 at 20:50

You need to store your replica in a class instance that can be accessed from QML. You can connect replica's signal to signal that you declared in the class then receive it from QML.

Please review the code below. (replicaexample.h, replicaexample.cpp and main.qml)

(Host Application is a console app and client is a QtQuick app.)

Host Application

"Hello! I am sending message, counter: 0"
"Hello! I am sending message, counter: 1"
"Hello! I am sending message, counter: 2"
"Hello! I am sending message, counter: 3"
"Hello! I am sending message, counter: 4"
"Hello! I am sending message, counter: 5"

ExampleReplica.rep

class ExampleRep
{
    SIGNAL(my_signal(QString message));
};

sourceexample.h

#ifndef SOURCEEXAMPLE_H
#define SOURCEEXAMPLE_H

#include <QTimer>
#include <QDebug>

#include "rep_ExampleReplica_source.h"

class SourceExample : public ExampleRepSimpleSource
{
    Q_OBJECT
public:
    SourceExample(QObject* parent = nullptr);
    ~SourceExample();

private Q_SLOTS:
    void _timerSlot();

private:
    int _counter;
    QTimer* _timer;
    QString _message;
};

#endif // SOURCEEXAMPLE_H

sourceexample.cpp

#include "sourceexample.h"

SourceExample::SourceExample(QObject* parent)
    : ExampleRepSimpleSource(parent)
    , _counter(0)
{
    _timer = new QTimer(this);
    _timer->setInterval(2000);
    connect(_timer, &QTimer::timeout, this, &SourceExample::_timerSlot);
    _timer->start();
}

SourceExample::~SourceExample()
{

}

void SourceExample::_timerSlot()
{
    _message = "Hello! I am sending message, counter: " + QString::number(_counter++);
    qInfo() << _message;
    Q_EMIT my_signal(_message);
}

main.cpp

#include <QCoreApplication>
#include <iostream>

#include "sourceexample.h"

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    SourceExample sourceObject;

    QRemoteObjectHost srcNode(QUrl(QStringLiteral("local:sourceNode")));
    srcNode.enableRemoting(&sourceObject);

    return a.exec();
}

Client Application

qml: console log: Hello! I am sending message, counter: 0
qml: console log: Hello! I am sending message, counter: 1
qml: console log: Hello! I am sending message, counter: 2
qml: console log: Hello! I am sending message, counter: 3
qml: console log: Hello! I am sending message, counter: 4
qml: console log: Hello! I am sending message, counter: 5

replicaexample.h

#ifndef REPLICAEXAMPLE_H
#define REPLICAEXAMPLE_H

#include <QObject>
#include <QSharedPointer>
#include <QDebug>

#include "rep_ExampleReplica_replica.h"

class ReplicaExample : public QObject
{
    Q_OBJECT
public:
    ReplicaExample(QSharedPointer<ExampleRepReplica> repNode, QObject* parent = nullptr);
    ~ReplicaExample();

Q_SIGNALS:
    void my_signal(QString message);

private:
    QSharedPointer<ExampleRepReplica> _repNode;
};

#endif // REPLICAEXAMPLE_H

replicaexample.cpp

#include "replicaexample.h"

ReplicaExample::ReplicaExample(QSharedPointer<ExampleRepReplica> repNode, QObject* parent)
    : QObject(parent)
    , _repNode(repNode)
{
    QObject::connect(_repNode.data(), &ExampleRepReplica::my_signal, this, &ReplicaExample::my_signal);
}

ReplicaExample::~ReplicaExample()
{

}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlEngine>
#include <QQmlContext>

#include "replicaexample.h"

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

    QSharedPointer<ExampleRepReplica> ptr;

    QRemoteObjectNode repNode;
    repNode.connectToNode(QUrl(QStringLiteral("local:sourceNode")));

    ptr.reset(repNode.acquire<ExampleRepReplica>());

    ReplicaExample client(ptr);

    QQmlApplicationEngine engine;
    const QUrl url(QStringLiteral("qrc:/main.qml"));
    engine.rootContext()->setContextProperty("repObject", &client);

    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

main.qml

import QtQuick 2.12
import QtQuick.Window 2.12

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

    Connections {
        target: repObject

        function onMy_signal(message) {
            console.log("console log: " + message)
        }
    }
}

How to emit signals from source to replica using QT Remote Objects

1 Answers1