Delegate Classes

Providing an Editor

In this example, when the table view needs to provide an editor, it asks the delegate to provide an editor widget that is appropriate for the item being modified. The createEditor() function is supplied with everything that the delegate needs to be able to set up a suitable widget:

    QWidget *SpinBoxDelegate::createEditor(QWidget *parent,
        const QStyleOptionViewItem &/* option */,
        const QModelIndex &/* index */) const
    {
        QSpinBox *editor = new QSpinBox(parent);
        editor->setMinimum(0);
        editor->setMaximum(100);
        editor->installEventFilter(const_cast<SpinBoxDelegate*>(this));

        return editor;
    }

Note that we do not need to keep a pointer to the editor widget because the view takes responsibility for destroying it when it is no longer needed.

We install the delegate's default event filter on the editor to ensure that it provides the standard editing shortcuts that users expect. Additional shortcuts can be added to the editor to allow more sophisticated behavior; these are discussed in the section on Editing Hints.

The view ensures that the editor's data and geometry are set correctly by calling functions that we define later for these purposes. We can create different editors depending on the model index supplied by the view. For example, if we have a column of integers and a column of strings we could return either a QSpinBox or a QLineEdit, depending on which column is being edited.

The delegate must provide a function to copy model data into the editor. In this example, we read the data stored in the display role, and set the value in the spin box accordingly.

    void SpinBoxDelegate::setEditorData(QWidget *editor,
                                        const QModelIndex &index) const
    {
        int value = index.model()->data(index, Qt::DisplayRole).toInt();

        QSpinBox *spinBox = static_cast<QSpinBox*>(editor);
        spinBox->setValue(value);
    }

In this example, we know that the editor widget is a spin box, but we could have provided different editors for different types of data in the model, in which case we would need to cast the widget to the appropriate type before accessing its member functions.

    void SpinBoxDelegate::setModelData(QWidget *editor, QAbstractItemModel *model,
                                       const QModelIndex &index) const
    {
        QSpinBox *spinBox = static_cast<QSpinBox*>(editor);
        spinBox->interpretText();
        int value = spinBox->value();

        model->setData(index, value);
    }

    void SpinBoxDelegate::updateEditorGeometry(QWidget *editor,
        const QStyleOptionViewItem &option, const QModelIndex &/* index */) const
    {
        editor->setGeometry(option.rect);
    }