QML access C++ model from parent component in nested object - c++

Question

I have a C++ list model, where I can read data properly
model.h
class Animal
{
public:
Animal(const QString &type, const QString &size);
//![0]
QString type() const;
QString size() const;
private:
QString m_type;
QString m_size;
//![1]
};
class AnimalModel : public QAbstractListModel
{
Q_OBJECT
public:
enum AnimalRoles {
TypeRole = Qt::UserRole + 1,
SizeRole
};
AnimalModel(QObject *parent = 0);
//![1]
void addAnimal(const Animal &animal);
int rowCount(const QModelIndex & parent = QModelIndex()) const;
QVariant data(const QModelIndex & index, int role = Qt::DisplayRole) const;
protected:
QHash<int, QByteArray> roleNames() const;
private:
QList<Animal> m_animals;
//![2]
};
model.cpp
#include "model.h"
Animal::Animal(const QString &type, const QString &size)
: m_type(type), m_size(size)
{
}
QString Animal::type() const
{
return m_type;
}
QString Animal::size() const
{
return m_size;
}
AnimalModel::AnimalModel(QObject *parent)
: QAbstractListModel(parent)
{
}
void AnimalModel::addAnimal(const Animal &animal)
{
beginInsertRows(QModelIndex(), rowCount(), rowCount());
m_animals << animal;
endInsertRows();
}
int AnimalModel::rowCount(const QModelIndex & parent) const {
Q_UNUSED(parent);
return m_animals.count();
}
QVariant AnimalModel::data(const QModelIndex & index, int role) const {
if (index.row() < 0 || index.row() >= m_animals.count())
return QVariant();
const Animal &animal = m_animals[index.row()];
if (role == TypeRole)
return animal.type();
else if (role == SizeRole)
return animal.size();
return QVariant();
}
//![0]
QHash<int, QByteArray> AnimalModel::roleNames() const {
QHash<int, QByteArray> roles;
roles[TypeRole] = "type";
roles[SizeRole] = "size";
return roles;
}
//![0]
main.cpp
#include "model.h"
#include <QGuiApplication>
#include <qqmlengine.h>
#include <qqmlcontext.h>
#include <qqml.h>
#include <QtQuick/qquickitem.h>
#include <QtQuick/qquickview.h>
//![0]
int main(int argc, char ** argv)
{
QGuiApplication app(argc, argv);
AnimalModel model;
model.addAnimal(Animal("Wolf", "Medium"));
model.addAnimal(Animal("Polar bear", "Large"));
model.addAnimal(Animal("Quoll", "Small"));
QQuickView view;
view.setResizeMode(QQuickView::SizeRootObjectToView);
view.setInitialProperties({{"model", QVariant::fromValue(&model)}});
//![0]
view.setSource(QUrl("qrc:view.qml"));
view.show();
return app.exec();
}
If I want to add a parent component to my listview, model is not accessible anymore because its visibility it's only from parent object. How can I expose the model then?
import QtQuick 2.0
import QtQuick.Window 2.15
//![0]
Window{
id: root
// how to catch here the model?
visible: true
width: 640
height: 480
ListView {
anchors.fill: parent
model: root.model // does not work
delegate: Text {
required property string type
required property string size
text: "Animal: " + type + ", " + size
}
}
}

Answer 1

Ok, that's really funny bug.
First of all, according to the Qt docs the property definition is:
[default] [required] [readonly] property <propertyType> <propertyName>
as you see the keyword property is mandatory.
The another issue is setInitialProperties says: Note: You can only use this function to initialize top-level properties.. So moving the ListView from the root item (and the model property too) makes this property inaccessible.
and one more issue is that the ListView already has a property named model, the attempt to redefine is incorrect. So you have to add some root item with the property model and that will solve the issue. Sure you will need to bind the ListView.model to this property
And the small example :)
Item {
id: root
width: 600
height: 400
property var model
ListView {
model: root.model
delegate: Text {
text: "Animal: " + type + ", " + size
}
}
}
Window can't be a root item since you use QQuickView.

Answer 2

Create an alias property in the root element with the same name of view.setInitialProperties allow to everything to work
main.cpp
view.setInitialProperties({{"mylistmodel", QVariant::fromValue(&model)}});
view.qml
import QtQuick 2.0
import QtQuick.Window 2.15
Window{
id: root
property alias mylistmodel : listView.model
visible: true
width: 640
height: 480
ListView {
id: listView
anchors.fill: parent
required model
delegate: Text {
required property string type
required property string size
text: "Animal: " + type + ", " + size
}
}
}