Accessing nested ListView with QQmlContext - c++

Question

I am trying to populate a QML ListView using a class that inherits QAbstractListModel. So far, I managed to create this using the QT Documentation here, under the "QAbstractItemModel subclass" section:
main.cpp
#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>
#include "gamemodel.h"
int main(int argc, char *argv[])
{
QGuiApplication app(argc, argv);
QQmlApplicationEngine engine;
GameModel model; //A class similar to AnimalModel in Qt Documentation.
//It contains a QList of Objects, each having 2 QString
//members (title and genre).
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));
model.readFile("c:/somePath/XML_G.xml"); //Initializing GameModel QList member
//using an XML file
QQmlContext *ctxt = engine.rootContext();
ctxt->setContextProperty("myModel", &model);
return app.exec();
}
main.qml
import QtQuick 2.5
import QtQuick.Window 2.2
Window
{
id: win
visible: true
width: 640
height: 480
title: qsTr("Hello World")
ListView
{
id: myList
width: parent.width
height: 50
clip: true
spacing: 5
orientation: ListView.Horizontal
model: myModel
delegate:
Rectangle
{
width: 150
height: 20
color: "#2255ff"
Text
{
text: gameTitle + " " + genre
}
}
}
}
Up to this point, my code works. However, if I try to change my main.qml file like this:
import QtQuick 2.5
import QtQuick.Window 2.2
Window
{
id: win
visible: true
width: 640
height: 480
title: qsTr("Hello World")
Item //ListView is now nested in this Item
{
ListView
{
id: myList
width: parent.width
height: 50
clip: true
spacing: 5
orientation: ListView.Horizontal
model: myModel
delegate:
Rectangle
{
width: 150
height: 20
color: "#2255ff"
Text
{
text: gameTitle + " " + genre
}
}
}
}
}
I end up being unable to set my model using ctxt->setContextProperty("myModel", &model);. From what little I can gather from the Qt Documentation (although I am most likely wrong), QQmlContext acts like a scope for the QML file. Thinking that, I tried changing this:
QQmlContext *ctxt = engine.rootContext();
to this:
QQmlContext *ctxt = engine.rootContext()->findChild<QQmlContext*>("list");
As well as setting my Item's objectName property to "list". Obviously, that failed, and it also caused a crash. Since my experience with QML is limited to the Qt Docs, I have been unsuccessful at finding a workaround. Is a solution using QQmlContext possible, or do I have to use QObject? If so, what would the QObject equivalent of ctxt->setContextProperty("myModel", &model) be?

Answer 1

The first argument of the setContextProperty() call is basically the "identifier" of the object, like the id property on the QML side.
You need to set that before accessing it in QML, otherwise it is unknown at the time of usage.
So you don't need any other call, but you need to do it before you load QML that needs it.
Just move it before the engine.load(...) line in your main.cpp

Answer 2

OK, apparently my problem was in my QML file. In my code, I setup my ListView like this:
width: parent.width
However, when I added an Item as the parent of my ListView, I forgot to set an initial width for my Item, thus turning ListView's width to 0. After I set an initial width for my Item, everything works as expected again.