Help with model for repeater

maxwell31

Hi,

I am trying to make a QML component for drawing x vs y plots. I am drawing the ticks and labels using a repeater in QML:

        Item {
            anchors.fill: parent
            visible: true
            Repeater {
                model:canvas.xTickPos.length
                Rectangle{
                    height: 4
                    width: 2
                    x: canvas.xTickPos[index]
                    y: parent.height-height
                    visible: true
                    color: "black"
                    border.width: 2
                }
              }
        }

Right now, as a model I am using a javascript array which is a property in the qml file. However, I would like to move the model to the c++ side, and I guess I should do it with a QStandardItemModel or a QAbstractItemModel. The model should contain two variables: tick position (a double) and label (a string). How would you write such a model?

Gojir4

Here is a minimal example:

myitemmodel.h

#ifndef MYITEMMODEL_H
#define MYITEMMODEL_H

#include <QAbstractListModel>

struct MyItem{
    double tickPos;
    QString label;
};

class MyItemModel : public QAbstractListModel
{
    Q_OBJECT
    enum roles{
        ROLE_TICK_POS = Qt::UserRole + 1,
        ROLE_LABEL,
    };
public:
    MyItemModel(QObject *parent = nullptr);

    // Basic functionality:
    int rowCount(const QModelIndex &parent = QModelIndex()) const override;
    QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
    virtual QHash<int,QByteArray> roleNames() const;

    QList<MyItem> items() const;
    void setItems(const QList<MyItem> &items);

private:
    QList<MyItem> m_items;

};

#endif // MyItemModel_H

myitemmodel.cpp

#include "MyItemmodel.h"

MyItemModel::MyItemModel(QObject *parent)
    : QAbstractListModel(parent)
{

}

int MyItemModel::rowCount(const QModelIndex &parent) const
{
    if (parent.isValid())
        return 0;

    return m_items.count();
}

QVariant MyItemModel::data(const QModelIndex &index, int role) const
{
    if (!index.isValid() || index.row() >= m_items.count())
        return QVariant();

    MyItem i = m_items.at(index.row());

    switch(role){
    case ROLE_TICK_POS: return i.tickPos;
    case ROLE_LABEL: return i.label;
    }

    return QVariant();
}

QHash<int, QByteArray> MyItemModel::roleNames() const
{
    QHash<int, QByteArray> roles;
    roles[ROLE_TICK_POS] = "role_tickPos";
    roles[ROLE_LABEL] = "role_label";
    return roles;
}

QList<MyItem> MyItemModel::items() const
{
    return m_items;
}

void MyItemModel::setItems(const QList<MyItem> &items)
{
    beginResetModel();
    m_items = items;
    endResetModel();
}

main.cpp:

MyItemModel myModel;
myModel.setItems(...);

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

Then in QML:

 Repeater {
        model: myModel
        Rectangle{
                height: 4
                width: 2
                x: role_tickPos  //Use role_label to access label value of the current item
                y: parent.height-height
                visible: true
                color: "black"
                border.width: 2
        }
}

I didn't compile it so it mays have some errors in the code.
As I said this is the minimal example but you can then add more features to the model if you need it.
Note that the model can also be a property of a QObject instances set as context property in QML engine.

maxwell31

Thank you very much!