Expose C++ Submodel to QML

[PavloPonomarov]

@KroMignon said in Expose C++ Submodel to QML:

I use since many years now a template class create by Thomas Boutrou which creates an QAbstractListModel by introspection of the base QObject.

Thank you. But I think those templates won't help in my case. I haven't found any possibility to build a multi-level model from the template

[GrecKo]

@PavloPonomarov said in Expose C++ Submodel to QML:

The issue here is that when I return this map from C++ it loses its connection to model and won't be updated in QML when the model is changed

Maybe you did something wrong there. Not sure about what you said about the slot and dataChanged signal, if that is done in QML, that's definitely not the correct way to do things. Anyway, using QStandardItemModel is fine for very basic PoC, if you need something more, it will get in the way and be more complicated than implementing your own model.

@PavloPonomarov said in Expose C++ Submodel to QML:

Thank you. But I think those templates won't help in my case. I haven't found any possibility to build a multi-level model from the template

If you have a QQmlObjectListModel of A and the class A has a property of type QQmlObjectListModel, you know have a multi-level model. I've done this multiple times.

I can't really help you more than that if you don't post a small self-sufficient code reproducing the problems you met.

[PavloPonomarov]

@GrecKo said in Expose C++ Submodel to QML:

Not sure about what you said about the slot and dataChanged signal

I've added a new role for the QVariantMap into my model, but to keep it up-to-date with model changes I had to create a slot connected to dataChanged of the model. It looks like this:

void MyModel::updateMap(const QModelIndex &topLeft, const QModelIndex &bottomRight, const QVector<int> &roles)
    bool changed = false;
    if(roles[0] == ItemObject) return; //ItemObject is a role
    QVariantMap item = topLeft.data(ItemObject).toMap();
    item[roleNames[roles[0]]] = topLeft.data(roles[0]); //roleNames[roles[0]] to get string representation
    itemFromIndex(topLeft)->setData(item, ItemObject);
}

Then I wrote an invokable function to get this map:

QVariant MyModel::getItem(const QModelIndex &index){
    return index.data(ItemObject);
}

And this is where the issue appears. I can call this function from QML, but is will return only current state of the map, without any binding.

@GrecKo said in Expose C++ Submodel to QML:

I can't really help you more than that if you don't post a small self-sufficient code reproducing the problems you met.

I will try to write a small example to my problem

[PavloPonomarov]

Here is the example:

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "mymodel.h"

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

    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    QQmlContext *context = engine.rootContext();
    myModel *model = new myModel();
    context->setContextProperty("myModel", model);
    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();
}

mymodel.h

#ifndef MYMODEL_H
#define MYMODEL_H

#include <QStandardItemModel>
#include <QObject>
#include <QDebug>

#define ROWS 10
#define NESTED 3
#define SUBITEMS 8

class myModel : public QStandardItemModel
{
    Q_OBJECT
public:
    myModel();
    void fillModel();

    QVariantMap getObject(const QModelIndex &index);
    QVariantMap getObject(QStandardItem *item);
    Q_INVOKABLE QVariant getQMLObject(const QModelIndex &index);
    Q_INVOKABLE void setValue(const QModelIndex &index, int value);
    enum Roles{
        Name=Qt::UserRole+1,
        Value,
        Description,
        QMLObject
    };
public slots:
    void updateObject(const QModelIndex &left, const QModelIndex &right, const QVector<int> &roles);
private:
     QHash<int, QByteArray> roleNames;
     QHash<int,QVector<QPersistentModelIndex>> m_Objects;
};

#endif // MYMODEL_H

mymodel.cpp

#include "mymodel.h"

myModel::myModel()
{
    roleNames[Name] = "name";
    roleNames[Value] = "value";
    roleNames[Description] = "description";
    roleNames[QMLObject] = "qmlObject";
    setItemRoleNames(roleNames);
    fillModel();
    connect(this, &QAbstractItemModel::dataChanged, this, &myModel::updateObject);
}

void myModel::fillModel()
{
    for(int i = 0; i < 3; i++){
        QStandardItem *item = new QStandardItem();
        item->setData("TreeParameter"+QString::number(i+1), Name);
        item->setData(i, Value);
        item->setData("Tree item"+QString::number(i+1), Description);
        item->setData(getObject(item), QMLObject);
        for(int j = 0; j < 8; j++){
            QStandardItem *subItem = new QStandardItem();
            subItem->setData("SubItem"+QString::number(j+1), Name);
            subItem->setData(j, Value);
            subItem->setData("Nested item"+QString::number(j+1), Description);
            subItem->setData(getObject(subItem), QMLObject);
            item->appendRow(subItem);
        }
        this->appendRow(item);
    }
    for(int i = 3; i < 10; i++){
        QStandardItem *item = new QStandardItem();
        item->setData("Parameter"+QString::number(i+1), Name);
        item->setData(i, Value);
        item->setData("Usual item"+QString::number(i+1), Description);
        item->setData(getObject(item), QMLObject);
        this->appendRow(item);
    }
}

QVariantMap myModel::getObject(const QModelIndex &index)
{
    return getObject(itemFromIndex(index));
}

QVariantMap myModel::getObject(QStandardItem *item)
{
    QVariantMap result;
    result[roleNames[Name]] = item->data(Name);
    result[roleNames[Value]] = item->data(Value);
    result[roleNames[Description]] = item->data(Description);
    return result;
}

QVariant myModel::getQMLObject(const QModelIndex &index)
{
    return index.data(QMLObject);
}

void myModel::setValue(const QModelIndex &index, int value)
{
    setData(index, value, Value);
}

void myModel::updateObject(const QModelIndex &left, const QModelIndex &right, const QVector<int> &roles)
{
    if(roles[0] == QMLObject) return;
    QVariantMap obj = left.data(QMLObject).toMap();
    obj[roleNames[roles[0]]] = left.data(roles[0]);
    setData(left, obj, QMLObject);
}

main.qml

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Layouts 1.12
import QtQuick.Controls 1.4 as QC1
import QtQuick.Controls 2.12
import QtQml.Models 2.11

Window {
    width: 640
    height: 280
    visible: true
    title: qsTr("Hello World")
    RowLayout{
        anchors.fill: parent
        QC1.TreeView{
            id: tree
            Layout.fillWidth: true;
            Layout.fillHeight: true;
            model: myModel
            selection: ItemSelectionModel{
                id:mySelectionModel
                model: myModel
            }
            itemDelegate: ItemDelegate{
                Text{
                    text: styleData.value
                }
                MouseArea{
                    anchors.fill: parent
                    onClicked:{
                        tree.selection.setCurrentIndex(styleData.index,ItemSelectionModel.SelectCurrent);
                        target.modelItem = myModel.getQMLObject(styleData.index);
                        target.modelIndex = styleData.index;
                    }
                }
            }
            QC1.TableViewColumn{
                width: 150
                title: "Name"
                role: "name"
            }
            QC1.TableViewColumn{
                width: 50
                title: "Value"
                role: "value"
                delegate: TextEdit{
                    text: styleData ? styleData.value : "";
                    Keys.onReturnPressed: {
                        focus = false;
                        myModel.setValue(styleData.index, text);
                    }
                }
            }
            QC1.TableViewColumn{
                width: 150
                title: "Description"
                role: "description"
            }
        }
        RowLayout{
            id: target
            Layout.fillWidth: true;
            property var modelIndex: false
            property var modelItem: false
            Rectangle{
                implicitHeight: 20
                implicitWidth: 65
                border.color: "black";
                border.width: 1
                TextEdit{
                    id: targetValue
                    anchors.fill: parent
                    horizontalAlignment: Text.AlignHCenter
                    verticalAlignment: Text.AlignVCenter
                    text: target.modelItem ? target.modelItem.value : "NaN"
                    Keys.onReturnPressed: {
                        targetValue.focus = false;
                        if(target.modelIndex) myModel.setValue(target.modelIndex, targetValue.text);
                    }
                }
            }
            TextArea{
                id: targetText
                readOnly: true
                implicitWidth: 130
                wrapMode: Text.Wrap
                text: target.modelItem ? target.modelItem.name : "Nothing yet"
            }
        }
    }
}

Guess I'll have to explain it a little bit. When I click an item of the model in TreeView its QMLObject role is sent to target component, where Value is given to TextEdit and Name is given to TextArea along with the QModelIndex of selected item. So when I change the value inside of TextEdit it updates the value in model. The issue here is that if I change the value inside TreeView it won't be updated in TextEdit, because target receives only a copy of QMLObject role through return index.data(QMLObject);. I know about possibility to pass QQmlDMAbstractItemModelData from TreeView to the taget, but I'm trying to bind model item to target directly, this TreeView is only to make this example more clear. Sorry, couldn't think of something smaller, guess I'm too deep in this topic to keep it simple