HorizontalHeaderView not reading data from headerData

[sandro4912]

I have the following constellation:

A QuestionSqlTableModel model which is based on QSqlTableModel.

A QuestionsProxyModel model which is based on QIdentityProxyModel

In Qml I expose QuestionsProxyModel it should work as an adaptor to adapt the role names in QML to the SQL columns in the QSqlTableModel.

Now this already looks like it works fine. I see the correct data of the QSqlTableModel in QML. However what does not work anymore is the HorizontalHeaderView.

In qml I disply the data like this in a tableView:

import QtQuick 2.15
import QtQuick.Controls 2.15
import QtQuick.Window 2.15
import Qt.labs.qmlmodels 1.0

import "data"

Item {
    id: root
    HorizontalHeaderView {
        id: horizontalHeaderView
        syncView: tableView
        anchors.left: tableView.left
    }
    TableView {
        id: tableView
        width: parent.width
        height: parent.height - horizontalHeaderView.height
        anchors.top: horizontalHeaderView.bottom
        boundsBehavior: Flickable.StopAtBounds

        reuseItems: true
        clip: true
        property var columnWidths: [60, 220, 220, 220, 220, 220, 100, 140]
        columnWidthProvider: function (column) {
            return columnWidths[column]
        }

        model: questionsProxyModel

        delegate: // Various delegates with Delegate Chooser ....

        ScrollBar.vertical: ScrollBar {}
    }
}

Now on start I get these errors with HorizontalHeaderView:

file:///home/sandro/Qt/5.15.0/gcc_64/qml/QtQuick/Controls.2/Universal/HorizontalHeaderView.qml:60:13: Unable to assign [undefined] to QString

The QuestionsProxyModel which is based on QIdentityProxyModel provides the header data like this:

#ifndef QUESTIONSPROXYMODEL_H
#define QUESTIONSPROXYMODEL_H

#include <QObject>
#include <QIdentityProxyModel>

class QuestionsProxyModel : public QIdentityProxyModel
{
    Q_OBJECT

    enum questionRoles {
        idRole = Qt::UserRole + 1,
        askedQuestionRole,
        answer1Role,
        answer2Role,
        answer3Role,
        answer4Role,
        correctAnswerRole,
        pictureRole
    };

public:
    QuestionsProxyModel(QObject* parent = nullptr);

    QHash<int, QByteArray> roleNames() const override;

    Q_INVOKABLE QVariant headerData(int section, Qt::Orientation orientation,
                                    int role) const override;

    Q_INVOKABLE QVariant data(const QModelIndex &index, int role) const override;

private:
    QModelIndex mapIndex(const QModelIndex &index, int role) const;
};

#endif // QUESTIONSPROXYQML_H

#include "../include/questionsproxymodel.h"

#include "../include/questionsqlcolumnnames.h"

#include <QPixmap>
#include <QBuffer>

#include <QByteArray>

QuestionsProxyModel::QuestionsProxyModel(QObject* parent)
    :QIdentityProxyModel(parent)
{
}

QHash<int, QByteArray> QuestionsProxyModel::roleNames() const
{
    QHash <int,QByteArray> roles;
    roles[idRole] = "id";
    roles[askedQuestionRole] = "askedQuestion";
    roles[answer1Role] = "answer1";
    roles[answer2Role] = "answer2";
    roles[answer3Role] = "answer3";
    roles[answer4Role] = "answer4";
    roles[correctAnswerRole] = "correctAnswer";
    roles[pictureRole] = "picture";

    return roles;
}

QVariant QuestionsProxyModel::headerData(int section,
                                         Qt::Orientation orientation, int role) const
{
    if(orientation != Qt::Orientation::Horizontal) {
        return QVariant{};
    }

    if(role == Qt::DisplayRole) {
        switch (section) {
            case 0:
                return tr("Id");
            case 1:
                return tr("Question");
            case 2:
                return tr("Answer 1");
            case 3:
                return tr("Answer 2");
            case 4:
                return tr("Answer 3");
            case 5:
                return tr("Answer 4");
            case 6:
                return tr("Correct Answer");
            case 7:
                return tr("Picture");
        }
    }
    return QVariant{};
}

QVariant QuestionsProxyModel::data(const QModelIndex &index, int role) const
{
    QModelIndex newIndex = mapIndex(index, role);
    if (role == idRole
            || role == askedQuestionRole
            || role == answer1Role
            || role == answer2Role
            || role == answer3Role
            || role == answer4Role
            || role == correctAnswerRole
            || role == pictureRole) {

        return QIdentityProxyModel::data(newIndex, Qt::DisplayRole);
    }
    return QIdentityProxyModel::data(newIndex, role);
}

QModelIndex QuestionsProxyModel::mapIndex(const QModelIndex &source, int role) const
{
    switch(role) {
    case idRole:
        return createIndex(source.row(), QuestionColumn::id);
    case askedQuestionRole:
        return createIndex(source.row(), QuestionColumn::askedQuestion);
    case answer1Role:
        return createIndex(source.row(), QuestionColumn::answer1);
    case answer2Role:
        return createIndex(source.row(), QuestionColumn::answer2);
    case answer3Role:
        return createIndex(source.row(), QuestionColumn::answer3);
    case answer4Role:
        return createIndex(source.row(), QuestionColumn::answer4);
    case correctAnswerRole:
        return createIndex(source.row(), QuestionColumn::correct_answer);
    case pictureRole:
        return createIndex(source.row(), QuestionColumn::picture);
    }
    return source;
}

I assumed that horizontalHeaderView calls QuestionsProxyModel::headerData but it does not even call it somehow.

The full code can be found here:
https://github.com/SandroWissmann/Quiz/tree/Editable-Question-Table

[sandro4912]

I think I found the reason why it is not working. The Qt docs state this for the model of headerView:

If the model is a QAbstractTableModel, then the header will display the model's horizontal headerData(); otherwise, the model's data().

So how do I have to implement data to show the headers? I tried this:

QVariant QuestionsProxyModel::data(const QModelIndex &index, int role) const
{
    if(role == Qt::DisplayRole) {
        switch (index.column()) {
            case 0:
                return tr("Id");
            case 1:
                return tr("Question");
            case 2:
                return tr("Answer 1");
            case 3:
                return tr("Answer 2");
            case 4:
                return tr("Answer 3");
            case 5:
                return tr("Answer 4");
            case 6:
                return tr("Correct Answer");
            case 7:
                return tr("Picture");
        }
    }
    
    QModelIndex newIndex = mapIndex(index, role);
    if (role == idRole
            || role == askedQuestionRole
            || role == answer1Role
            || role == answer2Role
            || role == answer3Role
            || role == answer4Role
            || role == correctAnswerRole
            || role == pictureRole) {

        return QIdentityProxyModel::data(newIndex, Qt::DisplayRole);
    }
    return QIdentityProxyModel::data(newIndex, role);
}

With the same result as before.

The hacky workarround was to set an own model on headerView with the names:

HorizontalHeaderView {
    id: horizontalHeaderView
    syncView: tableView
    anchors.left: tableView.left
    model: [qsTr("Id"), qsTr("Question"), qsTr("Answer 1"), qsTr(
            "Answer 2"), qsTr("Answer 3"), qsTr("Answer 4"), qsTr(
            "Correct Answer"), qsTr("Picture")]
}