How to update QAbstractItemModel view when a Data is updated - qt

Question

I use the Qt example for QAbstractItemModel and I try to update an Item to a given index.
I tried to use emit DataChangedbut it doesn't work, the view is not updated.
Here is an example:
What I want: When you click on the button, it will update Data at index 0, the type of the animal will be changed, it will become a Lion.
#include <QAbstractListModel>
#include <QStringList>
#include <qqmlcontext.h>
//![0]
class Animal
{
public:
Animal(const QString &type, const QString &size);
//![0]
QString type() const;
QString size() const;
void setType(QString q) {
m_type = q;
}
private:
QString m_type;
QString m_size;
//![1]
};
class AnimalModel : public QAbstractListModel
{
Q_OBJECT
public:
Q_INVOKABLE void test() ;
void setName(const QString &name);
enum AnimalRoles {
TypeRole = Qt::UserRole + 1,
SizeRole
};
AnimalModel(QObject *parent = 0);
//![1]
//!
//!
void setContext(QQmlContext *ctx) {
m_ctx = ctx;
}
void addAnimal(const Animal &animal);
int rowCount(const QModelIndex & parent = QModelIndex()) const;
QVariant data(const QModelIndex & index, int role = Qt::DisplayRole) const;
QHash<int, QByteArray> roleNames() const;
protected:
private:
QList<Animal> m_animals;
QQmlContext* m_ctx;
signals:
void dataChanged(const QModelIndex & topLeft, const QModelIndex & bottomRight);
//![2]
};
//![2]
model.h
#include "model.h"
#include "qDebug"
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();
}
void AnimalModel::test() {
m_animals[0].setType("Lion");
emit dataChanged(QModelIndex(),QModelIndex());
//I also tried:
QModelIndex topLeft = createIndex(0,0);
emit dataChanged(topLeft, topLeft);
}
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]
model.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);
QQmlContext *ctxt = view.rootContext();
ctxt->setContextProperty("myModel", &model);
//![0]
view.setSource(QUrl("qrc:view.qml"));
view.show();
return app.exec();
}
main.cpp
import QtQuick 2.0
import QtQuick 2.4
import QtQuick.Controls 1.3
import QtQuick.Window 2.2
import QtQuick.Dialogs 1.2
import QtQuick.Layouts 1.2
import QtQml.Models 2.1
import QtQuick.Controls.Styles 1.2
//![0]
ListView {
width: 200; height: 250
model: myModel
delegate: Text { text: "Animal: " + type + ", " + size }
MouseArea {
anchors.fill: parent
cursorShape: Qt.PointingHandCursor
onClicked: {
}
}
Button {
anchors.bottom: parent.bottom
width:50; height:50
text:"click"
onClicked: {
myModel.test()
}
}
}
//![0]
View.qml
Do you have any idea why it doesn't work ?
Thanks a lot !

Answer 1

Don't redefine signals in subclasses.
Remove the following lines (in model.h) and it should work as expected :
signals:
void dataChanged(const QModelIndex & topLeft, const QModelIndex & bottomRight);
Also this when calling dataChanged() you have to specify a valid QModelIndex. This is correct :
// I also tried:
QModelIndex topLeft = createIndex(0,0);
emit dataChanged(topLeft, topLeft);

Answer 2

You need create topLeft index and bottom right index and emit dataChanged. This update all model data in view.
QModelIndex topLeft = createIndex(0,0);
QModelIndex bottomRight = createIndex( rows count ,0);
emit dataChanged( topLeft, bottomRight );