Creating listview from QQuickItem in C++ - qt

Question

I am trying to make a listview component using QQuickItem and load its model using QAbstractListModel. Below are the steps which i tried.
listviewComponent.qml
ListView {
required model
delegate: Text {
required property string type
required property string size
text: type + ", " + size
}
}
Model.h
class Model
{
public:
Model(const QString& type, const QString& size);
QString type() const;
QString size() const;
private:
QString m_type;
QString m_size;
};
class CustomModel : public QAbstractListModel
{
Q_OBJECT
public:
enum Roles {
TypeRole = Qt::UserRole + 1,
SizeRole
};
CustomModel(QObject* parent = 0);
void addElement(const Model& pElement);
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<Model> m_list;
};
Model.cpp
Model::Model(const QString& type, const QString& size)
: m_type(type), m_size(size)
{
}
QString Model::type() const
{
return m_type;
}
QString Model::size() const
{
return m_size;
}
CustomModel::CustomModel(QObject* parent)
: QAbstractListModel(parent)
{
}
void CustomModel::addElement(const Model &pElement)
{
beginInsertRows(QModelIndex(), rowCount(), rowCount());
m_list << pElement;
endInsertRows();
}
int CustomModel::rowCount(const QModelIndex& parent) const {
Q_UNUSED(parent);
return m_list.count();
}
QVariant CustomModel::data(const QModelIndex& index, int role) const {
if (index.row() < 0 || index.row() >= m_list.count())
return QVariant();
const Model& mod = m_list[index.row()];
if (role == TypeRole)
return mod.type();
else if (role == SizeRole)
return mod.size();
return QVariant();
}
QHash<int, QByteArray> CustomModel::roleNames() const {
QHash<int, QByteArray> roles;
roles[TypeRole] = "type";
roles[SizeRole] = "size";
return roles;
}
Myclass.h
class myclass : public QObject
{
Q_OBJECT
public:
myclass();
inline int createUI(QQmlApplicationEngine &engine){
QQuickWindow *window = qobject_cast<QQuickWindow*>(engine.rootObjects().at(0));
if (!window) {
qFatal("Error: Your root item has to be a window.");
return -1;
}
QQuickItem *root = window->contentItem();
window->setWidth(600);
window->setHeight(500);
QQmlComponent listviewComp(&engine, QUrl(QStringLiteral("qrc:/listviewComponent.qml")));
CustomModel model;
model.addElement(Model("Wolf", "Medium"));
model.addElement(Model("Polar bear", "Large"));
model.addElement(Model("Quoll", "Small"));
QQuickItem *listview = qobject_cast<QQuickItem*>(listviewComp.createWithInitialProperties({ {"model", QVariant::fromValue(&model)} }));
QQmlEngine::setObjectOwnership(listview, QQmlEngine::CppOwnership);
listview->setParentItem(root);
listview->setParent(&engine);
listview->setProperty("objectName", "lv");
listview->setWidth(200);
listview->setHeight(100);
listview->setX(250);
listview->setY(30);
window->show();
return 0;
}
};
main.cpp
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
const QUrl url(QStringLiteral("qrc:/main.qml"));
engine.load(url);
QQmlContext *item = engine.rootContext();
myclass myClass;
item->setContextProperty("_myClass", &myClass);
myClass.createUI(engine);
return app.exec();
}
Problem: Listview is getting displayed but with only one row, but there are 3 rows added in CustomModel. I am assuming some problem with createWithInitialProperties, but couldnt able to crack it.

Answer 1

The problem is caused because "model" is a local variable that will be destroyed as soon as createUI is finished executing, and what you see as the first row is just a cache, you shouldn't actually see a row (it looks like a bug). The solution is to use the heap memory:
// ...
CustomModel *model = new CustomModel(window);
model->addElement(Model("Wolf", "Medium"));
model->addElement(Model("Polar bear", "Large"));
model->addElement(Model("Quoll", "Small"));
QQuickItem *listview = qobject_cast<QQuickItem*>(listviewComp.createWithInitialProperties({ {"model", QVariant::fromValue(model)} }));
// ...