Custom QItemDelegate works in QTableView but not QTreeView

[Joel Bodenmann]

I wrote a custom QItemDelegate to put a QCheckBox in a column of a QTableView which worked quite well:

#include <QCheckBox>
#include <QHBoxLayout>
#include "toolwidget/checkboxdelegate.h"

CheckboxDelegate::CheckboxDelegate(QObject* parent) : QItemDelegate(parent)
{
}

QWidget* CheckboxDelegate::createEditor(QWidget* parent, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    Q_UNUSED(option)
    Q_UNUSED(index)

    // Create a new checkbox. Use a layout to align (center) it.
    QCheckBox* editor = new QCheckBox(parent);
    editor->setObjectName("CheckBox");
    QHBoxLayout* layout = new QHBoxLayout;
    layout->addStretch();
    layout->addWidget(editor);
    layout->addStretch();
    QWidget* editorWidget = new QWidget(parent);
    editorWidget->setLayout(layout);

    return editorWidget;
}

void CheckboxDelegate::setEditorData(QWidget* editor, const QModelIndex& index) const
{
    // Retrieve the checked state from the item
    bool checked = index.model()->data(index, Qt::EditRole).toBool();

    // Retrieve the checkbox
    QCheckBox* checkbox = static_cast<QCheckBox*>(editor->findChild<QCheckBox*>("CheckBox"));
    if (!checkbox) {
        qCritical("CheckboxDelegate::setEditorData(): Couldn't retrieve QCheckBox. Aborting.");
        return;
    }

    // Set the checkbox state
    checkbox->setChecked(checked);
}

void CheckboxDelegate::setModelData(QWidget* editor, QAbstractItemModel* model, const QModelIndex& index) const
{
    QCheckBox* checkbox = static_cast<QCheckBox*>(editor->findChild<QCheckBox*>("CheckBox"));
    if (!checkbox) {
        qCritical("CheckboxDelegate::setModelData(): Couldn't retrieve QCheckBox. Aborting.");
        return;
    }

    // Set the model data
    model->setData(index, checkbox->isChecked(), Qt::EditRole);
}

void CheckboxDelegate::updateEditorGeometry(QWidget* editor, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    Q_UNUSED(index)

    editor->setGeometry(option.rect);
}

void CheckboxDelegate::paint(QPainter* painter, const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    // Retrieve the checked state from the item
    Qt::CheckState checkState = index.model()->data(index, Qt::DisplayRole).toBool() ? Qt::Checked : Qt::Unchecked;

    // Render
    drawCheck(painter, option, option.rect, checkState);
}

QSize CheckboxDelegate::sizeHint(const QStyleOptionViewItem& option, const QModelIndex& index) const
{
    Q_UNUSED(option)
    Q_UNUSED(index)

    QCheckBox checkbox;

    return checkbox.sizeHint();
}

Now I decided that I'd much rather use a QTreeView than a QTableView because I want to introduce hierarchies in my model. The problem is that my CheckboxDelegate doesn't work there anymore.
I still see the checkbox being rendered but I can't change the state of it anymore. When I click on it I see that QAbstractItemModel::setData() is being called successfully but it always writes back the same value - this means that the checkbox never gets toggled.

I'm a bit lost here. I don't know how much more information is required. Any ideas?

[SGaist]

Hi,

Out of curiosity, why not return item flag Qt::ItemIsUserCheckable from your model ? IIRC it should provide you with what you need directly and avoid the need of a custom delegate.

On a side note, you should use qobject_cast when dealing with QObject casting. static_cast doesn't do any validation.

[Joel Bodenmann]

I tried using Qt::ItemIsUserCheckable and it has the expected effect. However, instead of displaying a regular checkbox it displayed a combobox with the values "True" and "False". Hence the custom delegate.

I replaced the static_cast with qobject_cast as per your recommendation. Of course, as expected, this didn't affect the problem that I'm having.

Any ideas?

[SGaist]

You also need to modify your data function for the corresponding role.

See the "extending the read only example with roles" part of the model view tutorial here.

[Joel Bodenmann]

I also modified my model. Actually, when I was still using the QTableView I followed exactly the example you linked and I got it working. The reason why I created my own custom delegate anyway is because I want one single checkbox that is centered in the cell. The "built-in" feature (as shown in the example you linked) adds a checkbox to the decoration of a cell.

As mentioned everything works well in a QTableView. It's just that it doesn't work that well in a QTreeView.

[SGaist]

Can you setup a minimal project that shows the behavior ?

[Joel Bodenmann]

@SGaist

Yup, here you go: <link_removed>
I hope that helps... really lost here.

I am using Qt 5.6.1 on Windows 10 64-Bit with MinGW 4.9.2.

[Joel Bodenmann]

At the end, @SGaist pointed me to this implementation of a checkbox item delegate which works very well.