Example 1: Direct Connection using a Static Source

Create a source object

To create this Source object, first we create the definition file, simpleswitch.rep. This file describes the properties and methods for the object and is input to the Qt Remote Objects Compiler repc. This file only defines interfaces that are necessary to expose to the Replicas.

simpleswitch.rep

class SimpleSwitch
{
    PROP(bool currState=false);
    SLOT(server_slot(bool clientState));
};

In simpleswitch.rep,

currState holds the current state of the switch.
server_slot() allows us to interact with the source - it will be connected to the echoSwitchState(bool newstate) signal.

For repc to process this file, add the following line to your cmake file:

qt6_add_repc_sources(directconnectserver
    simpleswitch.rep
)

If you're using qmake:

REPC_SOURCE = simpleswitch.rep

These instructions are only relevant for the Qt Remote Object module, so you need to add it to your project as well. If you're using CMake, add:

find_package(Qt6 REQUIRED COMPONENTS RemoteObjects)
target_link_libraries(directconnectserver PRIVATE Qt6::RemoteObjects)

If you're using qmake:

QT       += remoteobjects

repc creates the rep_SimpleSwitch_source.h header in the build directory that you specify. For more information, see Source.

repc creates three helper classes for use with QtRO. For this example, we use the basic: SimpleSwitchSimpleSource. It's an abstract class, defined in rep_SimpleSwitch_source.h. We derive from it to define our SimpleSwitch implementation class as shown below:

simpleswitch.h

#ifndef SIMPLESWITCH_H
#define SIMPLESWITCH_H

#include "rep_simpleswitch_source.h"

class SimpleSwitch : public SimpleSwitchSimpleSource
{
    Q_OBJECT
public:
    SimpleSwitch(QObject *parent = nullptr);
    ~SimpleSwitch();
    virtual void server_slot(bool clientState);
public Q_SLOTS:
    void timeout_slot();
private:
    QTimer *stateChangeTimer;
};

#endif

In simpleswitch.h,

stateChangeTimer is a QTimer that is used to toggle the state of our SimpleSwitch.
timeout_slot() is connected to stateChangeTimer's timeout() signal.
server_slot() -- which is called automatically on the source whenever any replica calls their version of the slot -- outputs the received value.
currStateChanged(bool), defined in the repc-generated rep_SimpleSwitch_source.h, is emitted whenever currState toggles. In this example, we ignore the signal on the source side, and handle it later on the replica side.

The definition of our SwitchState class is shown below:

simpleswitch.cpp

#include "simpleswitch.h"

// constructor
SimpleSwitch::SimpleSwitch(QObject *parent) : SimpleSwitchSimpleSource(parent)
{
    stateChangeTimer = new QTimer(this); // Initialize timer
    QObject::connect(stateChangeTimer, &SimpleSwitch::timeout, this, &SimpleSwitch::timeout_slot); // connect timeout() signal from stateChangeTimer to timeout_slot() of simpleSwitch
    stateChangeTimer->start(2000); // Start timer and set timout to 2 seconds
    qDebug() << "Source Node Started";
}

//destructor
SimpleSwitch::~SimpleSwitch()
{
    stateChangeTimer->stop();
}

void SimpleSwitch::server_slot(bool clientState)
{
    qDebug() << "Replica state is " << clientState; // print switch state echoed back by client
}

void SimpleSwitch::timeout_slot()
{
    // slot called on timer timeout
    if (currState()) // check if current state is true, currState() is defined in repc generated rep_simpleswitch_source.h
        setCurrState(false); // set state to false
    else
        setCurrState(true); // set state to true
    qDebug() << "Source State is "<<currState();

}

Create a registry
Because this example uses a direct connection between nodes, we can omit this step.

Create a host node

The host node is created as shown below:

QRemoteObjectHost srcNode(QUrl(QStringLiteral("local:switch")));

Host source object and remoting

The following statements instantiate the Source object and pass it on to the host to enable "remoting", which is the process of making an object visible to the QtRO network:

SimpleSwitch srcSwitch; // create simple switch
srcNode.enableRemoting(&srcSwitch); // enable remoting

The contents of main.cpp file that implements the steps described above are as follows:

main.cpp

#include <QCoreApplication>
#include "simpleswitch.h"

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

    SimpleSwitch srcSwitch; // create simple switch

    QRemoteObjectHost srcNode(QUrl(QStringLiteral("local:switch"))); // create host node without Registry
    srcNode.enableRemoting(&srcSwitch); // enable remoting/sharing

    return a.exec();
}

Compile and run this source-side project. The output, without any replicas created, should look as shown below with the switch state toggling between true and false every two seconds.

"Example 1: Server Output"

The subsequent steps are for creating the replica side of the network, which in this example gets the state of switch from the Source and echoes it back.

Replica Code

Use repc to add a replica to your project
We use the same API definition file as we did on the source side, SimpleSwitch.rep, to create a Replica header file using the repc. If you're using cmake, include the following line in your client side cmake file, specifying a .rep file input:
```
qt6_add_repc_replicas(directconnectclient
    simpleswitch.rep
)
```
If you're using qmake, add the following line to your client side .pro file:
```
REPC_REPLICA = simpleswitch.rep
```
The repc tool generates a rep_SimpleSwitch_replica.h file in the build directory. For more information, see Replica.
Create a node to connect with the source's host node
The following code instantiates the second node on the network and connects it with the source host node:
```
QRemoteObjectNode repNode; // create remote object node
repNode.connectToNode(QUrl(QStringLiteral("local:switch"))); // connect with remote host node
```

Call the node's acquire() to create a pointer to a replica

First, we instantiate a replica:

QSharedPointer<SimpleSwitchReplica> ptr;
ptr.reset(repNode.acquire<SimpleSwitchReplica>()); // acquire replica of source from host node

Note: acquire() returns a pointer to the replica, but doesn't manage its lifetime. This example shows the recommended process of wrapping the returned pointer in a QSharedPointer or QScopedPointer to ensure that the pointer is always deleted properly.

main.cpp implements the steps described above and instantiates our object:

main.cpp

#include <QCoreApplication>
#include "client.h"

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

    QSharedPointer<SimpleSwitchReplica> ptr; // shared pointer to hold source replica

    QRemoteObjectNode repNode; // create remote object node
    repNode.connectToNode(QUrl(QStringLiteral("local:switch"))); // connect with remote host node

    ptr.reset(repNode.acquire<SimpleSwitchReplica>()); // acquire replica of source from host node

    Client rswitch(ptr); // create client switch object and pass reference of replica to it

    return a.exec();
}

The complete declaration and definition for the Client class is as follows:

client.h

#ifndef _CLIENT_H
#define _CLIENT_H

#include <QObject>
#include <QSharedPointer>

#include "rep_simpleswitch_replica.h"

class Client : public QObject
{
    Q_OBJECT
public:
    Client(QSharedPointer<SimpleSwitchReplica> ptr);
    ~Client();
    void initConnections();// Function to connect signals and slots of source and client

Q_SIGNALS:
    void echoSwitchState(bool switchState);// this signal is connected with server_slot(..) on the source object and echoes back switch state received from source

public Q_SLOTS:
    void recSwitchState_slot(); // slot to receive source state
private:
    bool clientSwitchState; // holds received server switch state
    QSharedPointer<SimpleSwitchReplica> reptr;// holds reference to replica

 };

#endif

client.cpp

#include "client.h"

// constructor
Client::Client(QSharedPointer<SimpleSwitchReplica> ptr) :
    QObject(nullptr),reptr(ptr)
{
    initConnections();
    //We can connect to SimpleSwitchReplica Signals/Slots
    //directly because our Replica was generated by repc.
}

//destructor
Client::~Client()
{
}

void Client::initConnections()
{
    // initialize connections between signals and slots

    // connect source replica signal currStateChanged() with client's recSwitchState() slot to receive source's current state
    QObject::connect(reptr.data(), &SimpleSwitchReplica::currStateChanged, this, &Client::recSwitchState_slot);
    // connect client's echoSwitchState(..) signal with replica's server_slot(..) to echo back received state
    QObject::connect(this, &Client::echoSwitchState, reptr.data(), &SimpleSwitchReplica::server_slot);
}

void Client::recSwitchState_slot(bool value)
{
    qDebug() << "Received source state "<< value << reptr.data()->currState();
    clientSwitchState = reptr.data()->currState();
    Q_EMIT echoSwitchState(clientSwitchState); // Emit signal to echo received state back to server
}

Compiling and running this example together with the source-side example generates the following output:

"Direct Connect Server Client Communication output"

Contents

Example 1: Direct Connection using a Static Source

Replica Code

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