Warning

This section contains snippets that were automatically translated from C++ to Python and may contain errors.

Example 1: Direct Connection using a Static Source#

Describes how the Qt Remote Objects establishes a direct connection using a static source. .. _qtro-example1: In this example, the source object is a simple binary switch that toggles its state based on a timer. When the state changes, a signal is emitted by the source which QtRO propagates to all replicas. Since the replicas have the same properties, signals, and slots as were exposed from the source, any slots connected to the replica’s signal will be called when the replica receives that signal. The client process then echoes back the received switch state to the source by emitting its own signal which is connected to a slot on the replica.

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
from rep_simpleswitch_source import *
class SimpleSwitch(SimpleSwitchSimpleSource):

    Q_OBJECT
# public
    SimpleSwitch(QObject parent = None)
    ~SimpleSwitch()
    def server_slot(clientState):
public Q_SLOTS:
    def timeout_slot():
# private
    stateChangeTimer = QTimer()

#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
from simpleswitch import *
# constructor
def __init__(self, SimpleSwitchSimpleSource(parent):

    stateChangeTimer = QTimer(self) # Initialize timer
    stateChangeTimer.timeout.connect(self.timeout_slot); // connect timeout() signal from stateChangeTimer to timeout_slot() of simpleSwitch
    stateChangeTimer.start(2000) # Start timer and set timout to 2 seconds
    print("Source Node Started")

#destructor
SimpleSwitch.~SimpleSwitch()

    stateChangeTimer.stop()

def server_slot(self, clientState):

    print("Replica state is ", clientState) # print switch state echoed back by client

def timeout_slot(self):

    # 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
    print("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:
srcNode = QRemoteObjectHost(QUrl("local:replica"))
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
from PySide6.QtCore import QCoreApplication
from simpleswitch import *
if __name__ == "__main__":

    a = QCoreApplication(argc, argv)
    SimpleSwitch srcSwitch # create simple switch
    # Create host node without Registry:
    srcNode = QRemoteObjectHost(QUrl("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#

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("local:replica")) # connect with remote host node

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

First, we instantiate a replica:

ptr = QSharedPointer()
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

from PySide6.QtCore import QCoreApplication
from client import *
if __name__ == "__main__":

    a = QCoreApplication(argc, argv)
    QSharedPointer<SimpleSwitchReplica> ptr # shared pointer to hold source replica
    QRemoteObjectNode repNode # create remote object node
    repNode.connectToNode(QUrl("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
from PySide6.QtCore import QObject

from rep_simpleswitch_replica import *
class Client(QObject):

    Q_OBJECT
# public
    Client(QSharedPointer<SimpleSwitchReplica> ptr)
    ~Client() override = default
    def initConnections():
Q_SIGNALS:
    def echoSwitchState(server_slot(..):
public Q_SLOTS:
    def recSwitchState_slot(bool):
# private
    bool clientSwitchState # holds received server switch state
    QSharedPointer<SimpleSwitchReplica> reptr# holds reference to replica

#endif

client.cpp

from client import *
# constructor
def __init__(self, ptr):
    QObject(None),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.

def initConnections(self):

    # initialize connections between signals and slots
    # connect source replica signal currStateChanged() with client's recSwitchState() slot to receive source's current state
    reptr.currStateChanged.connect(self.recSwitchState_slot)
    # connect client's echoSwitchState(..) signal with replica's server_slot(..) to echo back received state
    self.echoSwitchState.connect(reptr.server_slot)

def recSwitchState_slot(self, value):

    print("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: