QItemDelegate Class

The default delegate used by the standard views supplied with Qt associates each standard role (defined by Qt::ItemDataRole) with certain data types. Models that return data in these types can influence the appearance of the delegate as described in the following table.

If the default delegate does not allow the level of customization that you need, either for display purposes or for editing data, it is possible to subclass QItemDelegate to implement the desired behavior.

When subclassing QItemDelegate to create a delegate that displays items using a custom renderer, it is important to ensure that the delegate can render items suitably for all the required states; e.g. selected, disabled, checked. The documentation for the paint() function contains some hints to show how this can be achieved.

You can provide custom editors by using a QItemEditorFactory. The Color Editor Factory Example shows how a custom editor can be made available to delegates with the default item editor factory. This way, there is no need to subclass QItemDelegate. An alternative is to reimplement createEditor(), setEditorData(), setModelData(), and updateEditorGeometry(). This process is described in the Spin Box Delegate Example.

Since Qt 4.4, there are two delegate classes: QItemDelegate and QStyledItemDelegate. However, the default delegate is QStyledItemDelegate. These two classes are independent alternatives to painting and providing editors for items in views. The difference between them is that QStyledItemDelegate uses the current style to paint its items. We therefore recommend using QStyledItemDelegate as the base class when implementing custom delegates or when working with Qt style sheets. The code required for either class should be equal unless the custom delegate needs to use the style for drawing.

See also Delegate Classes, QStyledItemDelegate, QAbstractItemDelegate, Spin Box Delegate Example, Settings Editor Example, Icons Example

if the delegate should clip the paint events

This property will set the paint clip to the size of the item. The default value is on. It is useful for cases such as when images are larger than the size of the item.

Access functions:

• bool hasClipping() const

• void setClipping(bool clip)

Constructs an item delegate with the given parent.

Destroys the item delegate.

Reimplements: QAbstractItemDelegate::createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const.

Returns the widget used to edit the item specified by index for editing. The parent widget and style option are used to control how the editor widget appears.

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Renders the item background for the given index, using the given painter and style option.

Renders a check indicator within the rectangle specified by rect, using the given painter and style option, using the given state.

Renders the decoration pixmap within the rectangle specified by rect using the given painter and style option.

Renders the item view text within the rectangle specified by rect using the given painter and style option.

Renders the region within the rectangle specified by rect, indicating that it has the focus, using the given painter and style option.

Reimplements: QAbstractItemDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index).

Reimplements: QObject::eventFilter(QObject *watched, QEvent *event).

Returns true if the given editor is a valid QWidget and the given event is handled; otherwise returns false. The following key press events are handled by default:

• Tab

• Backtab

• Enter

• Return

• Esc

In the case of Tab, Backtab, Enter and Return key press events, the editor's data is committed to the model and the editor is closed. If the event is a Tab key press the view will open an editor on the next item in the view. Likewise, if the event is a Backtab key press the view will open an editor on the previous item in the view.

If the event is a Esc key press event, the editor is closed without committing its data.

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Returns the editor factory used by the item delegate. If no editor factory is set, the function will return null.

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Reimplements: QAbstractItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const.

Renders the delegate using the given painter and style option for the item specified by index.

When reimplementing this function in a subclass, you should update the area held by the option's rect variable, using the option's state variable to determine the state of the item to be displayed, and adjust the way it is painted accordingly.

For example, a selected item may need to be displayed differently to unselected items, as shown in the following code:

    if (option.state & QStyle::State_Selected)
        painter->fillRect(option.rect, option.palette.highlight());

    const int size = qMin(option.rect.width(), option.rect.height());
    const int brightness = index.model()->data(index, Qt::DisplayRole).toInt();
    const double radius = (size / 2.0) - (brightness / 255.0 * size / 2.0);
    if (qFuzzyIsNull(radius))
        return;

    painter->save();
    painter->setRenderHint(QPainter::Antialiasing, true);
    painter->setPen(Qt::NoPen);
    if (option.state & QStyle::State_Selected)
        painter->setBrush(option.palette.highlightedText());
    else
    ...

After painting, you should ensure that the painter is returned to its the state it was supplied in when this function was called. For example, it may be useful to call QPainter::save() before painting and QPainter::restore() afterwards.

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Reimplements: QAbstractItemDelegate::setEditorData(QWidget *editor, const QModelIndex &index) const.

Sets the data to be displayed and edited by the editor from the data model item specified by the model index.

The default implementation stores the data in the editor widget's user property.

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Sets the editor factory to be used by the item delegate to be the factory specified. If no editor factory is set, the item delegate will use the default editor factory.

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Reimplements: QAbstractItemDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const.

Gets data from the editor widget and stores it in the specified model at the item index.

The default implementation gets the value to be stored in the data model from the editor widget's user property.

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Reimplements: QAbstractItemDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const.

Returns the size needed by the delegate to display the item specified by index, taking into account the style information provided by option.

When reimplementing this function, note that in case of text items, QItemDelegate adds a margin (i.e. 2 * QStyle::PM_FocusFrameHMargin) to the length of the text.

Reimplements: QAbstractItemDelegate::updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const.

Updates the editor for the item specified by index according to the style option given.