Exposing QList to QML

Question

I am trying to expose QList with custom objects (Sample) into QML. Whenever I store those custom objects (they inherits form QObject) into QList<QObject *>, they show up, but without info, but when I try expose them as a QList<Sample *>, they don't.

sample.h

class Sample : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString getVar READ getVar WRITE setVar NOTIFY varChanged)
public:
    explicit Sample();

    //! Returns var
    QString getVar() const { return var; }

    //! Sets var
    void setVar(const QString &a);

signals:
    varChanged();

protected:
    QString var;
};

Class containing list looks like this

samplecontrol.h

class SampleManager : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QList<Sample *> getSampleList READ getSampleList NOTIFY sampleListChanged)
public:
    SampleManager(const QString &path);

    //! Returns sample list
    QList<Sample *> getSampleList() const { return sampleList_; }

signals:
    sampleListChanged();

protected:
    QList<Sample *> sampleList_;
};

I am setting context with

view_->rootContext()->setContextProperty("slabGridModel", QVariant::fromValue(samplecontrol.getSampleList()));

As I said, when i tired

QList<QObject *> datalist;
datalist.append(sampleManager.getSampleList().first());
datalist.append(sampleManager.getSampleList().last());

it worked. How can I make it work with QList<Sample *>?

Thanks for your help!

Answer 1

You can pass a list of QObjects, but the problem is that it will not notify the view if more elements are added, if you want the view to be notified you must use a model that inherits from QAbstractItemModel. On the other hand how are you doing the datamodel as qproperty it is better to expose the SampleManager:

samplemodel.h

#ifndef SAMPLEMODEL_H
#define SAMPLEMODEL_H

#include "sample.h"

#include <QAbstractListModel>

class SampleModel : public QAbstractListModel
{
    Q_OBJECT
public:
    using QAbstractListModel::QAbstractListModel;
    ~SampleModel(){
        qDeleteAll(mSamples);
        mSamples.clear();
    }
    int rowCount(const QModelIndex &parent = QModelIndex()) const override{
        if (parent.isValid())
            return 0;
        return mSamples.size();
    }

    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override{
        if (!index.isValid())
            return QVariant();
        if(role == Qt::UserRole){
            Sample *sample =  mSamples[index.row()];
            return QVariant::fromValue(sample);
        }
        return QVariant();
    }

    void appendSample(Sample * sample)
    {
        beginInsertRows(QModelIndex(), rowCount(), rowCount());
        mSamples << sample;
        endInsertRows();
    }

    QHash<int, QByteArray> roleNames() const{
        QHash<int, QByteArray> roles;
        roles[Qt::UserRole] = "sample";
        return roles;
    }

private:
    QList<Sample *> mSamples;
};


#endif // SAMPLEMODEL_H

samplemanager.h

#ifndef SAMPLEMANAGER_H
#define SAMPLEMANAGER_H

#include "samplemodel.h"

#include <QObject>

class SampleManager : public QObject
{
    Q_OBJECT
    Q_PROPERTY(SampleModel* model READ model WRITE setModel NOTIFY modelChanged)
public:
    using QObject::QObject;
    SampleModel *model() const{
        return mModel.get();
    }
    void setModel(SampleModel *model){
        if(mModel.get() == model)
            return;
        mModel.reset(model);
    }
signals:
    void modelChanged();
private:
    QScopedPointer<SampleModel> mModel;
};

#endif // SAMPLEMANAGER_H

main.cpp

#include "samplemanager.h"
#include "samplemodel.h"

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

#include <QTime>
#include <QTimer>

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

    QGuiApplication app(argc, argv);

    SampleManager manager;
    manager.setModel(new SampleModel);

    // test
    QTimer timer;
    QObject::connect(&timer, &QTimer::timeout, [&manager](){
        manager.model()->appendSample(new Sample(QTime::currentTime().toString()));
    });
    timer.start(1000);

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

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

    GridView {
        anchors.fill: parent
        model: manager.model
        delegate:
            Rectangle {
            width: 100
            height: 100
            color: "darkgray"
            Text {
                text: sample.getVar
                anchors.centerIn: parent
            }
        }
    }
}

The complete example can be found in the following link.