How to access nested QStandardItemModel's items from QML? - c++

Question

Background
I have a tree-like QStandardItemModel, whose items I would like to access from QML.
Here is how the model is defined on the C++ side:
backend.h
class Backend : public QObject
{
Q_OBJECT
Q_PROPERTY(QStandardItemModel *model READ model CONSTANT)
public:
explicit Backend(QObject *parent = nullptr);
QStandardItemModel *model() const;
private:
QStandardItemModel *m_model;
};
backend.cpp
Backend::Backend(QObject *parent) :
QObject(parent),
m_model(new QStandardItemModel(this))
{
auto *itemFirst = new QStandardItem(tr("First"));
auto *itemSecond = new QStandardItem(tr("Second"));
auto *subItem = new QStandardItem(tr("First_02"));
subItem->appendRow(new QStandardItem("First_02_01"));
itemFirst->appendRow(new QStandardItem(tr("First_01")));
itemFirst->appendRow(subItem);
itemFirst->appendRow(new QStandardItem(tr("First_03")));
itemSecond->appendRow(new QStandardItem(tr("Second_00")));
itemSecond->appendRow(new QStandardItem(tr("Second_01")));
m_model->appendRow(itemFirst);
m_model->appendRow(itemSecond);
}
QStandardItemModel *Backend::model() const
{
return m_model;
}
The model is exported to QML in main.cpp like this:
Backend backend;
QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("backend", &backend);
qmlRegisterUncreatableType<QStandardItemModel>("QStandardItemModel", 1, 0, "QStandardItemModel", "The model should be created in C++");
Using TreeView from QtQuick.Controls 1.4 in main.qml like this:
TreeView {
anchors.fill: parent
model: backend.model
TableViewColumn {
title: "Name"
role: "display"
}
}
I get the desired results, i.e. all items nested correctly:
Problem
When I try to manually iterate over the nested items using Repeater and DelegateModel like this:
ColumnLayout {
anchors.fill: parent
Repeater {
model: backend.model
Item {
Layout.fillWidth: true
Layout.fillHeight: true
ColumnLayout {
anchors.fill: parent
Text {
color: "blue"
text: model.display
}
Repeater {
model: DelegateModel {
model: backend.model
rootIndex: modelIndex(index)
Item {
Layout.fillWidth: true
Layout.fillHeight: true
ColumnLayout {
anchors.fill: parent
Text {
color: "green"
text: model.display
}
Repeater {
model: DelegateModel {
model: backend.model
rootIndex: modelIndex(index)
Text {
color: "red"
text: model.display
}
}
}
}
}
}
}
}
}
}
}
the main branches (marked with blue) and the items on the first nesting level (marked with green) are the right ones, but I get the wrong items on the second nesting level (marked with red):
How to fix the code to correctly iterate over the QStandardItemModel's items on each nesting level?

Answer 1

The problem is in these two lines: rootIndex: modelIndex(index).
index is the index of the 'parent' model, but modelIndex(...) is the method of the current model.
I've tried it with this (slightly modified) piece of code and it worked:
Repeater {
model: DelegateModel {
id: model1
model: backend.model
delegate: ColumnLayout{
Text {
text: "Data: " + display
}
Repeater {
model: DelegateModel {
id: model2
model: backend.model
// 'index' comes from 'model1', so use the 'modelIndex' method from 'model1'
rootIndex: model1.modelIndex(index)
delegate: ColumnLayout{
Text {
text: "- Data: " + display
}
Repeater {
model: DelegateModel {
id: model3
model: backend.model
// 'index' comes from 'model2', so use the 'modelIndex' method from 'model2'
rootIndex: model2.modelIndex(index)
delegate: Text {
text: "-- Data: " + display
}
}
}
}
}
}
}
}
}