QStringList in QML?

[MScottM]

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

[raven-worx]

@MScottM said in QStringList in QML?:

myCppClassQstringList[0]

like any other list in JS

[MScottM]

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

[J.Hilk]

hi @MScottM

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

[MScottM]

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.

[J.Hilk]

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

[MScottM]

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.

[J.Hilk]

@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

[MScottM]

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:

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.

[MScottM]

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!

[J.Hilk]

@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
    }
}

[MScottM]

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?

[J.Hilk]

@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 😉

[MScottM]

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);
}

[MScottM]

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.