ContextProperty of QQmlPropertyMap object is not writable at qml

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Hello
I have a conventional QQmlPropertyMap of contextproeprty working pretty well at qml ( is being read pretty well )
but at the qml side I am not able to write any new value to it . what could be the reason of making QQmlPropertyMap object is not writable at qml side ?

here is the C++ code side:

Code:

QQmlPropertyMap* gDataProp;
int main(int argc, char *argv[])
{
    set_qt_environment();
    QGuiApplication app(argc, argv);
    ControlObjTreeModel  uiObjectTreeMod;
    gDataProp =new QQmlPropertyMap();  
    gDataProp->insert(mapNumOfSchObj,0);
    QJsonObject paramObj ={{shcObjName,"K0"} };
    QJsonObject paramIns[3];
    QJsonObject paramOut[2];
 
    paramIns[0]={{ portName,"IN0"} , { portID,1}};
    paramIns[1]={{ portName,"IN1"} , { portID,2}};
    paramIns[2]={{ portName,"IN2"} , { portID,3}};
 
    paramOut[0]={{ portName,"Out0"} , { portID,1}};
    paramOut[1]={{ portName,"Out1"} , { portID,2}};
 
    GroupObject gIns  [3];
    GroupObject gOuts [2];
 
    qDebug() <<paramObj;
 
    knx1 =new InterfaceObject(gDataProp,&paramObj ,paramIns, paramOut, gIns,gOuts ,3,2);
    paramObj[shcObjName]="Sw";
    sw1 =new InterfaceObject(gDataProp,&paramObj ,paramIns, paramOut, gIns,gOuts ,3,2);
 
    QQmlApplicationEngine engine;
    const QUrl url(u"qrc:/qt/qml/Main/main.qml"_qs);
 
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        &app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        },
        Qt::QueuedConnection);
 
    // BOLDFACE by OP for emphasis (Mod.)
    engine.rootContext()->setContextProperty("gDatPr", gDataProp );
    //
 
    engine.addImportPath(QCoreApplication::applicationDirPath() + "/qml");
    engine.addImportPath(":/");
    engine.load(url);
 
    if (engine.rootObjects().isEmpty()) {
        return -1;
    }
 
    return app.exec();
}
 
InterfaceObject:: InterfaceObject(QQmlPropertyMap * dmap ,QJsonObject* objParams
                                 , QJsonObject* insParam , QJsonObject* outsParam,
                                 GroupObject *inGo ,GroupObject *outGo, uint16_t numIns , uint16_t numOuts)
    :QObject (dmap)
{
    int numOfSchObj ;
    schDataMap=  dmap;
    interfaceData= new QJsonObject (*objParams);
    numOfIns=numIns;
    numOfOuts=numOuts;
    qDebug()<<*interfaceData;
 
    numOfSchObj =schDataMap->value(mapNumOfSchObj).toInt();
    interfaceData->insert(shcObjID,numOfSchObj+1);
 
    ins = new InterfacePort*[numIns];
    outs = new InterfacePort*[numOuts];
 
    for (uint16_t  i=0;i<numIns;i++)
    {
        ins [i]=new InterfacePort(insParam[i], inGo[i]);
        jsonArrayIn.push_back(ins [i]->getPortObj());
    }
 
    interfaceData->insert(shcObjIns,jsonArrayIn);
    interfaceData->insert(shcObjNumOfIns,numOfIns);
    qDebug()<<*interfaceData;
 
    for (uint16_t  i=0;i<numOuts;i++)
    {
        outsParam[i].insert(pConnectionTarObjID,-2);
        outsParam[i].insert(pConnectionTarPortID,-4);
        outs [i]=new InterfacePort(outsParam[i], outGo[i]);
        jsonArrayIn2.push_back(outs[i]->getPortObj());
    }
 
    interfaceData->insert(shcObjOuts,jsonArrayIn2);
    interfaceData->insert(shcObjNumOfOuts,numOfOuts);
 
    objKey=new QString (mapSchObjHeader + QString::number(numOfSchObj));
    schDataMap->insert(*objKey ,  *interfaceData);
 
    // BOLDFACE by OP for emphasis (Mod.)
    schDataMap->insert( mapNumOfSchObj ,numOfSchObj+1);
 
 
    schDataMap->connect(
        schDataMap,
        &QQmlPropertyMap::valueChanged,
        this,
        &InterfaceObject::updateFromGuiSlot);
    // end boldface
 
}

and in qml Side:
gDatPr["SO0"] [api.shcObjName]="newName"
console.log( "test Name ",gDatPr["SO0"] [api.shcObjName])

console.log is still showing the old name "K0"

*** Moderator's note: inserted CODE tags for readability. I apologize that embedded boldface font is not supported in CODE sections. Hopefully my added comments will help.

26th January 2025, 16:58
d_stranz

Re: ContextProperty of QQmlPropertyMap object is not writable at qml

Everything that you are doing in this main() code is happening before the Qt event loop starts running (app.exec()). If the QML <-> C++ interaction depends on Qt events, signals, and slots, then nothing that happens before the event loop is running will have any effect.

So you need a QMainWindow or some other GUI where this code runs, after the QMainWindow constructor has exited and the GUI is active (eg. after the showEvent()).

Re: ContextProperty of QQmlPropertyMap object is not writable at qml

Quote:

Originally Posted by d_stranz

Everything that you are doing in this main() code is happening before the Qt event loop starts running (app.exec()). If the QML <-> C++ interaction depends on Qt events, signals, and slots, then nothing that happens before the event loop is running will have any effect.

So you need a QMainWindow or some other GUI where this code runs, after the QMainWindow constructor has exited and the GUI is active (eg. after the showEvent()).

Many thanks for your support Mr. d_stranz ... I missed the Threading model at this small test..
I got the Thread model running OK but I am still not able to write any new value the QQmlPropertyMap object at qml side !!
here is the new C++ code:

Code:

MainWindowCC * mWindow;
 QTranslator trans1;
int main(int argc, char *argv[])
{
    set_qt_environment();
    QGuiApplication app(argc, argv);
    mWindow = new MainWindowCC (& app ,&trans1);
    mWindow->start();
 
 
    return app.exec();
}
 
MainWindowCC::MainWindowCC(QGuiApplication *app, QTranslator *mtrans)
 
     : QThread()
{
    gDataProp =new QQmlPropertyMap();
    gDataProp->insert(mapNumOfSchObj,0);
    QJsonObject paramObj ={{shcObjName,"K0"} };
    QJsonObject paramIns[3];
    QJsonObject paramOut[2];
 
    paramIns[0]={{ portName,"IN0"} , { portID,1}};
    paramIns[1]={{ portName,"IN1"} , { portID,2}};
    paramIns[2]={{ portName,"IN2"} , { portID,3}};
 
    paramOut[0]={{ portName,"Out0"} , { portID,1}};
    paramOut[1]={{ portName,"Out1"} , { portID,2}};
 
    GroupObject gIns  [3];
    GroupObject gOuts [2];
 
    qDebug() <<paramObj;
 
    knx1 =new InterfaceObject(app,gDataProp,&paramObj ,paramIns, paramOut, gIns,gOuts ,3,2);
    knx1->start();
    paramObj[shcObjName]="Sw";
    sw1 =new InterfaceObject(app,gDataProp,&paramObj ,paramIns, paramOut, gIns,gOuts ,3,2);
    sw1->start();
 
    const QUrl url(u"qrc:/qt/qml/Main/main.qml"_qs);
 
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreated,
        app,
        [url](QObject *obj, const QUrl &objUrl) {
            if (!obj && url == objUrl)
                QCoreApplication::exit(-1);
        },
        Qt::QueuedConnection);
 
    engine.rootContext()->setContextProperty("gDatPr", gDataProp );
    engine.rootContext()->setContextProperty("uiObjectTreeModel", &uiObjectTreeMod );
 
    engine.addImportPath(QCoreApplication::applicationDirPath() + "/qml");
    engine.addImportPath(":/");
    engine.load(url);
 
}
 
 
InterfaceObject:: InterfaceObject(QGuiApplication *app,QQmlPropertyMap * dmap ,QJsonObject* objParams
                                 , QJsonObject* insParam , QJsonObject* outsParam,
                                 GroupObject *inGo ,GroupObject *outGo, uint16_t numIns , uint16_t numOuts)
    :QThread ()
{
    int numOfSchObj ;
    schDataMap=  dmap;
    interfaceData= new QJsonObject (*objParams);
    numOfIns=numIns;
    numOfOuts=numOuts;
    qDebug()<<*interfaceData;
 
    numOfSchObj =schDataMap->value(mapNumOfSchObj).toInt();
    interfaceData->insert(shcObjID,numOfSchObj+1);
 
    ins = new InterfacePort*[numIns];
    outs = new InterfacePort*[numOuts];
 
    for (uint16_t  i=0;i<numIns;i++)
    {
        ins [i]=new InterfacePort(insParam[i], inGo[i]);
        jsonArrayIn.push_back(ins [i]->getPortObj());
    }
 
    interfaceData->insert(shcObjIns,jsonArrayIn);
    interfaceData->insert(shcObjNumOfIns,numOfIns);
    qDebug()<<*interfaceData;
 
    for (uint16_t  i=0;i<numOuts;i++)
    {
        outsParam[i].insert(pConnectionTarObjID,-2);
        outsParam[i].insert(pConnectionTarPortID,-4);
        outs [i]=new InterfacePort(outsParam[i], outGo[i]);
        jsonArrayIn2.push_back(outs[i]->getPortObj());
    }
 
    interfaceData->insert(shcObjOuts,jsonArrayIn2);
    interfaceData->insert(shcObjNumOfOuts,numOfOuts);
 
    objKey=new QString (mapSchObjHeader + QString::number(numOfSchObj));
    schDataMap->insert(*objKey ,  *interfaceData);
    schDataMap->insert( mapNumOfSchObj ,numOfSchObj+1);
 
 
    QObject::connect(
        schDataMap,
        &QQmlPropertyMap::valueChanged,
        this,
        &InterfaceObject::updateFromGuiSlot);
 
}
 
void  InterfaceObject::updateFromGuiSlot(const QString &key, const QVariant &value)
{
    qDebug ()<<"Obj:"<<*objKey<<" before conditionhas been updated .. I am in its slot now";
    if(key==*objKey)
    {
        qDebug ()<<"Obj:"<<*objKey<<" has been updated .. I am in its slot now";
    }
}
void  InterfaceObject::run()
{
    while(loopActive==true)
    {
        //
 
    }
}

and in the qml side:

Code:

gDatPr["SO0"] [api.shcObjName]="new Name"
    console.log( "test Name: ",gDatPr["SO0"] [api.shcObjName])

console is still showing the old name ("test Name: K0")

wha t could be the reason that QQmlPropertyMap object is not connected with its valueChanged Event , and not writable at qml side_

27th January 2025, 17:25
d_stranz

Re: ContextProperty of QQmlPropertyMap object is not writable at qml

It still looks to me as though you are executing all of this code before the event loop is running. Things that happen in your MainWindowCC and InterfaceObject constructors are taking place before app.exec() (which starts the event loop). Your connect() statements set up signal-slot connections, but any signals emitted are ignored if the event loop is not running.

Anyway, if that isn't the problem, I can't be of much more help. I don't use qml and do not have any experience with it. What I am saying is from my own experience with C++ and unsuccessfully trying to use signals and slots before an event loop is running.
28th January 2025, 08:53
AmerQ

Re: ContextProperty of QQmlPropertyMap object is not writable at qml
Quote:

Originally Posted by d_stranz

It still looks to me as though you are executing all of this code before the event loop is running. Things that happen in your MainWindowCC and InterfaceObject constructors are taking place before app.exec() (which starts the event loop). Your connect() statements set up signal-slot connections, but any signals emitted are ignored if the event loop is not running.

Anyway, if that isn't the problem, I can't be of much more help. I don't use qml and do not have any experience with it. What I am saying is from my own experience with C++ and unsuccessfully trying to use signals and slots before an event loop is running.

Hello Mr.d_stranz
Many thanks for your support.
it seems that qml doesn't accept writing to multilevel JSON object like the next anymore:
Code:

gDatPr["SO0"] [api.shcObjName]="newName"
but it do accept :
Code:

var tempVar=gDatPr["SO0"] tempVar[api.shcObjName] ="newName" gDatPr["SO0"] =tempVar
i tworked like this , and the connected signal/slots are working as well