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 .pro file:

    REPC_SOURCE = simpleswitch.rep

    The REPC_SOURCE variable is only relevant for the Qt Remote Object module, so you need to add it to your project as well:

    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, SIGNAL(timeout()), this, SLOT(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:switch")));
  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
    
        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

  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. Include the following line in your client side .pro file, specifying a .rep file input:

    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:switch"))); // 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: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(), SIGNAL(currStateChanged()), this, SLOT(recSwitchState_slot()));
           // connect client's echoSwitchState(..) signal with replica's server_slot(..) to echo back received state
            QObject::connect(this, SIGNAL(echoSwitchState(bool)),reptr.data(), SLOT(server_slot(bool)));
    }
    
    void Client::recSwitchState_slot()
    {
        qDebug() << "Received source state "<<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"

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