[SOLVED] Updating single item in CppModel does not update QML

[ortogonal]

Hi!

I've made a simple example which have a data model (class derived from QStandardItemModel). I've connected the model from C++ into the QML using setContextProperty(). Every thing works fine as long as I just "display" the model.

But when I start to update the data in an item it does not update the QML. I've made a simple connection (using Connections element) in QML that connects the models dataChanged signal. I see that signal in the QML when I update the model, but still the Text-element in the ListView delegate will not update.

This is my code:
main.cpp
@#include <QtGui/QGuiApplication>
#include "qtquick2applicationviewer.h"
#include "cppmodel.h"
#include "cppmodelitem.h"

#include <qqmlengine.h>
#include <qqmlcontext.h>
#include <QtQuick/qquickview.h>

int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);

CppModel model;
model.appendRow(new CppModelItem("Item 1"));
model.appendRow(new CppModelItem("Item 2"));
model.appendRow(new CppModelItem("Item 3"));


QtQuick2ApplicationViewer viewer;
viewer.rootContext()->setContextProperty("cppModel",  &model);
viewer.setMainQmlFile(QStringLiteral("qml/datamodeltest/main.qml"));
viewer.showExpanded();

return app.exec();

}
@

cppmodel.cpp
@#include "cppmodel.h"
#include "cppmodelitem.h"

#include <QDebug>

CppModel::CppModel()
{
CppModelItem dummy("");
this->setItemRoleNames(dummy.roleNames());
}

void CppModel::changeItem(int i)
{
if( this->rowCount() > i )
{
qDebug() << "using new data for row" << i;

    // This will NOT update the QML-Viewer with the new data.
    // But I can see the dataChanged signal within the QML code.
    this->item(i, 0)->setData("newData", CppModelItem::NameRole);

    // Appending row will make the QML-Viewer update
    //this->appendRow(new CppModelItem("Test"));
}

}
@

cppmodelitem.cpp
@#include "cppmodelitem.h"

CppModelItem::CppModelItem(const QString& name)
{
m_name = name;

this->setEditable(true);

}

QHash<int, QByteArray> CppModelItem::roleNames() const
{
QHash<int, QByteArray> names;
names[NameRole] = "name";
return names;
}

QVariant CppModelItem::data(int r) const
{
Roles role = (Roles)r;
switch(role)
{
case NameRole:
return m_name;
break;
default:
return QVariant();
}
}
@

main.qml
@import QtQuick 2.0

Rectangle {
width: 360
height: 360

ListView {
    id: listView
    anchors.fill: parent

    delegate: Text {
        height: 18
        width: 360
        text: name

        MouseArea {
            anchors.fill: parent
            onClicked: cppModel.changeItem(index)
        }
    }

    model: cppModel
}

Connections {
    target: listView.model
    onDataChanged: {
        console.log("Changing data")
    }
}

}
@

When I run the program I get this debug
@using new data for row 1
Changing data
using new data for row 2
Changing data@

To me that says that the C++ function changeItem() is invoked and the connection between C++ and QML is there, but how will I get the Element in the delegate to update?

Thanks!

[t3685]

Have you tried emitting a signal to notify that data has changed?

[ortogonal]

I've this Connections
@
Connections {
target: listView.model
onDataChanged: {
console.log("Changing data")
}
}
@

And I can see the log "Changing data". And as far as I understand QStandardItemModel will do the emitting of signals by it self, right?

[t3685]

I believe you still have to emit the signal yourself. Here is a thread with a similar problem:

http://qt-project.org/forums/viewthread/24294

The "Changing data" you see could have come from a different function that changes the data and not neccessarily from your changeItem function.
(I could always be wrong of course :))

[ortogonal]

Nothing :-(

I've added the following line to my changeItem() function right after the setData() call.

@
emit this->dataChanged(createIndex(i,0), createIndex(i,0));
@

The only difference is that I now see to "Chaning data" logs that probably comes from the added the extra emit.

[t3685]

Have you had a look at this link?

I believe it does something similar to what you're trying to do:

http://www.developer.nokia.com/Community/Wiki/Using_QStandardItemModel_in_QML

[ortogonal]

Sorry, but I can't see why that link would help.

[t3685]

I was thinking you could try out the model they provided to see if it would work with your QML file. Guess I should have been more clearer :)

[ortogonal]

I solved it!
To make it work I implemented my own setData() in CppModelItem, which seems really straight-forward when you think of it!

@
void CppModelItem::setData(const QVariant &value, int role)
{
if( role == NameRole )
{
m_name = value.toString();

    this->model()->dataChanged(this->index(), this->index());
}

}
@

In the setData() I call the models dataChanged() with this index and everything works!