Example 1: Direct Connection using a Static Source

1. 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();
       void server_slot(bool clientState) override;
   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, &QTimer::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();
   
   }

2. Create a registry

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

3. Create a host node

   The host node is created as shown below:

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

4. 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
   
       // Create host node without Registry:
       QRemoteObjectHost srcNode(QUrl(QStringLiteral("local:replica")));
       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.

   

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

1. 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.

2. 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:replica"))); // connect with remote host node

3. 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:replica"))); // 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() override = default;
       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(bool); // 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)
   {
       // Connect signal for replica initialized with initialization slot.
       initConnections();
       // We can connect to SimpleSwitchReplica Signals/Slots
       // directly because our Replica was generated by repc.
   }
   
   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: