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QStringList in QML?



  • Is is possible to access items of a QStringList from QML? I want to do something like this:

    Label {
        id: label1
        text: myCppClassQstringList.index0
    }
    Label {
        id: label2
        text: myCppClassQstringList.index1
    }
    

    I've read that QStringList can be handled by QML natively, but I can't find any examples of how to do it.

    Best regards,

    Scott


  • Moderators

    @MScottM said in QStringList in QML?:

    myCppClassQstringList[0]
    

    like any other list in JS



  • I can't seem to get access to the QStringList. I've tried various methods of exposing the variable to QML but I can't seem to make it work. It seems like it should be REALLY simple!

    I've exposed the class to QML using engine.rootContext:

    moduleFinder modFinder;
    
        engine.rootContext()->setContextProperty("modFinder", &modFinder);
    
    

    and from QML I can call the function that loads the QStringList:

    signal setModule(var lblMsg)
    
    Button {
            id: clickme
            x: 170
            y: 0
            visible: true
            height: 100
            width: 300
            text: "click me"
            onClicked: setModule("Module1")
        }
        onSetModule: {modFinder.setModule(lblMsg)     
        }
    

    I know this part is working, my QStringList gets loaded with the appropriate list of strings.

    When I try to set the QML labels' text using the resulting QStringList - nothing works. I've tried exposing the variable with Q_PROPERTY, etc.

    If someone could lead me a little further down the path, I would appreciate it!

    Best regards.

    By the way - thank you for your reply @raven-worx


  • Moderators

    hi @MScottM

    can you show us a bit more, how your c++ class looks like?



  • Yes - moduleFinder.h:

    #ifndef MODULEFINDER_H
    #define MODULEFINDER_H
    
    #include <QObject>
    #include <QStringListModel>
    
    class moduleFinder : public QObject
    {
        Q_OBJECT
        Q_PROPERTY(QStringList moduleIo MEMBER m_moduleIo NOTIFY moduleIoChanged)
    
    public:
        explicit moduleFinder( QObject *parent = nullptr );
    
        QString fileName = "list.txt";
        QString module;
        QStringList ioList;
        QStringList moduleIo;    
    
        Q_INVOKABLE void loadModules();
        QStringList getIo(QString);
        int index = 0;
        int newIndex = 0;
    
    public slots:
        Q_INVOKABLE void setModule( const QString m_module );
    
    signals:
        void moduleIoChanged(const QStringList &newModuleIoList);
        
    private:
       
    };
    
    #endif // MODULEFINDER_H
    

    moduleFinder.cpp:

    #include "modulefinder.h"
    #include <QFile>
    #include <QDebug>
    
    moduleFinder::moduleFinder(QObject *parent) : QObject(parent)
    {}
    
    void moduleFinder::setModule(QString m_module) {
        module = m_module;
        getIo(module);
    }
    
    void moduleFinder::loadModules(){
        QFile moduleFile(fileName);
    
        if (!moduleFile.exists()) {
            qWarning() << "file doesn't exist!";}
        else if (!moduleFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
            qWarning() << "Not open"; }
        else {
            QTextStream textStream(&moduleFile);
            while (!textStream.atEnd())
                ioList << textStream.readLine();
            moduleFile.close();
        }   
    }
    
    QStringList moduleFinder::getIo(QString myModule) {
        //qDebug()<<myModule;
        int lines = ioList.length();
        QString moduleId = myModule;
        for (int i=0;i<lines;i++) {
            //qDebug()<< "IO List" <<ioList.at(i);
            if (ioList.at(i).contains(moduleId)) { // if module is found in list
                index = i; // get index of position in list
            }
        }
        newIndex = index + 32;
        for (int y=index+1; y<newIndex+1; ++y) { // and copy relevant lines into new list
            moduleIo << ioList.at(y); //   <-this is the QStringList I want to access
        }    
        emit moduleIoChanged(m_moduleIo);
        //qDebug()<< moduleIo;
    }
    

    loadModules() is run once from main.cpp when the program starts.


  • Moderators

    @MScottM
    I'm surprised this actually compiles, as your class has no member m_moduleIo the member variable is called moduleIo



  • Oh, I put it under 'private':

    private:
        QStringList m_moduleIo;
    

    I had been trying a couple different things to get something to work - I copied and pasted the code above from between a change I had tried.


  • Moderators

    @MScottM
    I have some difficulties to follow your problem.

    Does this simple example help you?

    //main.cpp
    #include <QApplication>
    #include <QQmlApplicationEngine>
    
    #include "myclass.h"
    #include "QQmlContext"
    
    int main(int argc, char *argv[])
    {
        QApplication app(argc, argv);
    
        QQmlApplicationEngine engine;
    
        myClass mClass;
    
        engine.rootContext()->setContextProperty("cppListModel", &mClass);
    
        engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
        if (engine.rootObjects().isEmpty())
            return -1;
    
        return app.exec();
    }
    
    //main.qml
    import QtQuick 2.9
    import QtQuick.Window 2.2
    import QtQuick.Controls 2.5
    
    Window {
        visible: true
        width: 640
        height: 480
        title: qsTr("Hello World")
    
        id:root
    
    
        ListView{
            id: listView
            anchors.fill: parent
    
            model: cppListModel.myListModel
            delegate:Text {
                text: modelData
                color: index % 2 ? "red" : "blue"
            }
        }
    }
    
    
    //myClass
    #ifndef MYCLASS_H
    #define MYCLASS_H
    
    #include <QObject>
    
    class myClass : public QObject
    {
        Q_OBJECT
        Q_PROPERTY(QStringList myListModel READ myListModel WRITE setMyListModel NOTIFY myListModelChanged)
    public:
        explicit myClass(QObject *parent = nullptr) :QObject(parent)
        {
            setMyListModel({"Item1", "Item2", "Item3", "Item4"});
        }
    
    
        QStringList myListModel() const
        {
            return m_myListModel;
        }
    
    signals:
    
        void myListModelChanged(QStringList myListModel);
    
    public slots:
    
    
    void setMyListModel(QStringList myListModel)
    {
        if (m_myListModel == myListModel)
            return;
    
        m_myListModel = myListModel;
        emit myListModelChanged(m_myListModel);
    }
    
    private:
    
    QStringList m_myListModel;
    };
    
    #endif // MYCLASS_H
    


  • Hi @J-Hilk,

    Thank you for your example - I apologize for not being more clear in what I'm trying to do. I have a GUI that I want to display the inputs and outputs of the modules of a PLC, so that when a user clicks the module button, the main page updates with that modules' list of I/O.

    An over-simplified example:

    0_1563283804617_9963df82-e5c0-4373-a592-cb0c69e47631-image.png

    I can't get a ListView to work because it displays the whole list at a time, so I am trying to access a QStringList by index and put each indexes text in a corresponding label.

    I hope that better explains the problem I'm having!

    Best regards.



  • I've made some progress following a different track!

    I was able to bring the QStringList into QML by using a function to create an array:

    Button {
            id: clickme
            x: 170
            y: 0
            visible: true
            height: 100
            width: 300
            text: "click me"
            onClicked: {setModule( "Module1" ); readlistValues.readValues(modFinder.moduleIo);
            }
        }
        onSetModule: { modFinder.setModule(lblMsg) }    
    

    I had to create a property for each index value:

    property string label1Text: ""
    

    then assign them:

    Item {
            id: readlistValues
            function readValues(anArray) {
                for (var i=0; i<32; i++)
                    console.log("list: ", anArray[i])
                    label1Text = anArray[0]
            }
        }
    

    Now 'anArray' contains my list!! And I can assign the text as I hoped.

    Label {
            id: myLabel
            x: 270
            y: 106
            width: 100
            height: 50
            text: label1Text
            horizontalAlignment: Text.AlignHCenter
            verticalAlignment: Text.AlignVCenter
        }
    

    I followed information on this page:
    Data Type conversion Between QML and c++

    I'm sure I need to test this more, but I'm getting closer!


  • Moderators

    @MScottM

    like this ? (I only changed the main.qml from the previous example)

    import QtQuick 2.9
    import QtQuick.Window 2.2
    import QtQuick.Controls 2.5
    
    Window {
        visible: true
        width: 640
        height: 480
        title: qsTr("Hello World")
    
        id:root
    
    
        Button{
            id:list1
            anchors{
                left:parent.left
                top:parent.top
                right:parent.horizontalCenter
                margins: 2
                rightMargin: 1
            }
            height: width / 3
    
            text: qsTr("Set Model1")
    
            onClicked:cppListModel.myListModel = ["Left 1", "Left 2"]
            background: Rectangle{
                color: cppListModel.myListModel[0] === "Left 1" ? "red" : "grey"
            }
        }
    
        Button{
            id:list2
            anchors{
                left:parent.horizontalCenter
                top:parent.top
                right:parent.right
                margins: 2
                leftMargin: 1
            }
            height: width / 3
    
            text:  qsTr("Set Model2")
    
            onClicked:cppListModel.myListModel = ["Right 1", "Right 2"]
    
            background: Rectangle{
                color: cppListModel.myListModel[0] === "Right 1" ? "red" : "grey"
            }
        }
    
        Text {
            id: entry1
            text: cppListModel.myListModel[0]
    
            anchors{
                left: parent.left
                right: parent.right
                top: list1.bottom
                margins: 2
            }
            height: list1.height
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignHCenter
        }
        Text {
            id: entry2
            text: cppListModel.myListModel[1]
    
            anchors{
                left: parent.left
                right: parent.right
                top: entry1.bottom
                margins: 2
            }
            height: list1.height
    
            verticalAlignment: Text.AlignVCenter
            horizontalAlignment: Text.AlignHCenter
        }
    }
    

    0_1563339030826_9779f82f-26ed-4c4a-bab3-3a534d28e954-image.png

    0_1563339041241_027063d4-1562-48a2-a9bb-5a0f12d19d4f-image.png

    0_1563339052858_85112240-72a7-4654-951a-a6c867c711d8-image.png



  • Hi @J-Hilk,

    That is the right behavior, but not the way I'm hoping to go about it. It looks like you are updating the list from the QML button?

    In my 'real' application there will be something like 30 pieces of information to update on each button press, and like 20 possible modules (as I said - my example was over-simplified!). That is why I'm hoping to use a text file. Something like a config file that can be changed by a user as needed to update the I/O lists.

    I think I can actually mark this one as solved, as I can now access the list from the QML side and set my labels' text. Now my issue is that even though the list updates on the c++ side, it doesn't change in QML after the first button press.

    Shall I open a new question?


  • Moderators

    @MScottM said in QStringList in QML?:

    It looks like you are updating the list from the QML button

    yes, but it doesn't matter what updates the list, as long as setMyListModelis called

    I think I can actually mark this one as solved, as I can now access the list from the QML side and set my labels' text. Now my issue is that even though the list updates on the c++ side, it doesn't change in QML after the first button press.

    hey, at least progress ;)

    Shall I open a new question?

    You can, but this could continue as well

    Can you create a minimal compellable example? Should simplify things drastically 😉



  • I figured out what is happening! It's in this function:

    QStringList moduleFinder::getIo(QString myModule) {
        //qDebug() << "my Module from QML" << myModule; 
        int lines = ioList.length();
        //qDebug() << "lines:" << lines;                
        QString moduleId = myModule;
        for (int i=0;i<lines;i++) {
            //qDebug() << "IO List" << ioList.at(i);
            if (ioList.at(i).contains(moduleId)) {      
                index = i;                             
            }
        }
        newIndex = index + 32;
        qDebug()<<"Index:" << index;                   
        qDebug()<<"New Index:" << newIndex;             
        for (int y=index+1; y<newIndex+1; ++y) {
      // PROBLEM IS HERE
      //m_moduleIo is being appended with a new list each time
            m_moduleIo << ioList.at(y);
      // I need to check and clear it at each access, but not sure how!?
            qDebug() << "io List" << ioList.at(y);      
        }
        emit moduleIoChanged(m_moduleIo);              
        qDebug()<< "m_moduleIO" << m_moduleIo;          
        return m_moduleIo;
        //emit moduleIoChanged(m_moduleIo);
    }
    
    


  • Update:

    <smacks own forehead>

    QStringList moduleFinder::getIo(QString myModule) {   
        int lines = ioList.length();            
        QString moduleId = myModule;
        for (int i=0;i<lines;i++) {        
            if (ioList.at(i).contains(moduleId)) {      
                index = i;                             
            }
        }
        newIndex = index + 32;    
        m_moduleIo.clear();  //<- RESET BEFORE EACH TIME THROUGH      
        for (int y=index+1; y<newIndex+1; ++y) {  
            m_moduleIo << ioList.at(y);  
            qDebug() << "io List" << ioList.at(y);      
        }
        emit moduleIoChanged(m_moduleIo);          
        return m_moduleIo;    
    }
    

    It all works as I hoped now.


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