dynamic number of models

[Marek]

Hi
On QML side I have dynamic number of ListView, each of them needs data from Cpp, is there w way to provide dynamic number of models from Cpp ? Other than having QML ListModel in QML and fetch the data from Cpp by some javascript functions? All ListView require the same model but with different data

Something like:

foreach(ccpModel in models) {
   cppModel=new MyModel()
   cppModel->loadData()
   engine->rootContext()->setContextProperty("MyModel1",cppModel)
}

and when I need different models, delete old one, "unsetContextProperty" or just set it again with the same name "MyModel1" but pointing to different QObject ?

And how do I tell QML ListView to use this model?

property var my_model: "MyModel"+number 
model: my_model

is this doable or do I need javascript and QML ListModel ?

Best Regards
Marek

[LeLev]

@Marek you can use QVariantList as list of models in QML if it fits your requirement, however I don't know how efficient this will be with complex/large models.

class Backend : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QVariantList models READ models WRITE setModels NOTIFY modelsChanged)
public:
    explicit Backend(QObject *parent = nullptr);

    QVariantList models() const
    {
        return m_models;
    }
    void setModels(QVariantList models)
    {
        if (m_models == models)
            return;
        m_models = models;
        emit modelsChanged();
    }

signals:
    void modelsChanged();
private :
    QVariantList m_models;  
};


//--------------------------
   Backend backend;
  
    QVariantList myModels;
    QStringList model1;
    model1 << "item1";
    model1 << "item2";
    model1 << "item3";
    myModels.append(QVariant::fromValue(model1));

    QStringList model2;
    model2 << "item7";
    model2 << "item8";
    model2 << "item9";
    myModels.append(QVariant::fromValue(model2));
    backend.setModels(myModels);

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

//------------------------
 property var _models : backend.models

    Connections{
        target: backend
        function onModelsChanged (){
            _models = backend.models
        }
    }

 Column{
        anchors.fill: parent
        spacing: 20
        Repeater{
            model: 2
            Rectangle{
                height: 200
                width: 300
                border.width: 1
                color: "grey"
                ListView{
                    model: _models[index]
                    anchors.fill: parent
                    delegate: Text {
                        height: 20
                        text: modelData
                    }
                }
            }
        }
    }

[Marek]

@LeLev Thanks for hint
What if I need some more complex model, I mean instead of
model1 << "item1"

data with role names:

QString model_data="{
                    \"id_role\" : fe_id,
                    \"name_role\" : some_name
                    \"more_role\" : some_data}"
model1 << model_data;

Would this work? Speed is not required, there won't be many elements in the models

best,
Marek

[LeLev]

see
https://doc.qt.io/qt-5/qtquick-modelviewsdata-cppmodels.html#:~:text=Models can be defined in,a QObjectList or a QAbstractItemModel.

[Marek]

@LeLev Need a little help here
I'm using QAbstractListModel daily, but this list of models does not work for me.
It does not report any errors, just does not display anything, If I expose individual model like SingleModel0 to QML it works, but as a list of models it does not.
Can someone take a look, maybe I'm doing something wrong
Below individual files
main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "backend-models.h"
#include "single-model.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);

    QGuiApplication app(argc, argv);

    QVariantList list;

    QQmlApplicationEngine engine;
    BackendModels backendModels;
    for(int i=0;i<3;i++) {
        SingleModel *model=new SingleModel(&app,i);
        list.append(QVariant::fromValue(model));
        engine.rootContext()->setContextProperty(QString("SingleModel%1").arg(i),model);
    }
    backendModels.setModels(list);
    engine.rootContext()->setContextProperty("BackendModels",&backendModels);


    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

backend-models.h

#include <QtCore>

class BackendModels : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QVariantList models READ models WRITE setModels NOTIFY modelsChanged)
public:
    explicit BackendModels(QObject *parent = nullptr);

    QVariantList models() const;
    void setModels(QVariantList models);
signals:
    void modelsChanged();
private :
    QVariantList m_models;
};

backend-models.cpp

#include "backend-models.h"

BackendModels::BackendModels(QObject *parent):QObject(parent) {

}
QVariantList BackendModels::models() const {
    return m_models;
}
void BackendModels::setModels(QVariantList models)
{
    if (m_models == models)
        return;
    m_models = models;
    emit modelsChanged();
}

single-model.h

#include <QObject>
#include <QtCore>

struct SingleDataStruct {
    int     id;
    QString name;
};

class SingleModel : public QAbstractListModel
{
    Q_OBJECT
public:

    enum ItemRoles {
        IdRole = Qt::UserRole + 1,
        NameRole = Qt::UserRole + 2,
        RowRole=Qt::UserRole+3
    };

    SingleModel(QObject* parent,int idx);

    virtual int rowCount(const QModelIndex&) const;
    virtual QVariant data(const QModelIndex &index, int role) const;
    QHash<int, QByteArray> roleNames() const;
    QVariant getRoleData(int role, int row) const;

public slots:

signals:
private slots:

private:
    QVector<SingleDataStruct*> modelVector;
    QHash<int, QByteArray> roles;
};

single-model.cpp

#include "single-model.h"

SingleModel::SingleModel(QObject* parent,int idx) : QAbstractListModel (parent)
{
    roles[IdRole] = "id_role";
    roles[RowRole] = "row_role";
    roles[NameRole] = "name_role";

    SingleDataStruct *p;
    for(int i=0;i<10;i++) {
        p=new SingleDataStruct;
        p->id=i*10+idx;
        p->name=QString("name1_%1").arg(p->id);
        modelVector.append(p);
    }
}

int SingleModel::rowCount(const QModelIndex&) const {
    return modelVector.count();
}

QHash<int, QByteArray> SingleModel::roleNames() const {
    return roles;
}

QVariant SingleModel::data(const QModelIndex &index, int role) const {
    if(!index.isValid()) {
        return QVariant();
    }
    if(roles.contains(role) && modelVector.value(index.row(),nullptr)!=nullptr) {
        return getRoleData(role,index.row());
    }
    return QVariant();
}
QVariant SingleModel::getRoleData(int role, int row) const {
    SingleDataStruct *p = modelVector.at(row);

    switch(role) {
    case IdRole:
        return QVariant(p->id);
    case NameRole:
        return QVariant(p->name);
    case RowRole:
        return QVariant(row);
    default:
        qWarning()<<"SingleModel::getRoleData there is no role:" << role;
    }
    return QVariant();
}

Main.qml

import QtQuick 2.12
import QtQuick.Window 2.12

Window {
    visible: true
    width: 640
    height: 480
    title: qsTr("Hello World")


    ListView {
        id:listView0
        anchors.top: parent.top
        anchors.left: parent.left
        anchors.right: parent.right
        height:100
        orientation: ListView.Horizontal
        spacing: 20
        model:BackendModels.models[0]
        delegate: Rectangle {
            height:parent.height
            width:height
            color:"blue"
            Text {
                anchors.fill: parent
                text: name_role
            }
        }
    }
    ListView {
        id:listView1
        anchors.top: listView0.bottom
        anchors.left: parent.left
        anchors.right: parent.right
        height:100
        orientation: ListView.Horizontal
        spacing: 20
        model:BackendModels.models[1]
        delegate: Rectangle {
            height:parent.height
            width:height
            color:"green"
            Text {
                anchors.fill: parent
                text: name_role
            }
        }
    }
    ListView {
        id:listView2
        anchors.top: listView1.bottom
        anchors.left: parent.left
        anchors.right: parent.right
        height:100
        orientation: ListView.Horizontal
        spacing: 20
        model:BackendModels.models[2]
        delegate: Rectangle {
            height:parent.height
            width:height
            color:"yellow"
            Text {
                anchors.fill: parent
                text: name_role
            }
        }
    }
}

Best
Marek

[LeLev]

@Marek said in dynamic number of models:

model:BackendModels[1]

BackendModels is your object, you need the Q_PROPERTY models of that object, so please try
model:BackendModels.models [1]

[Marek]

@LeLev Great it works!
I have edited and corrected Main.qml in previous post.
Many Thanks
Marek