QItemDelegate Class | Qt Widgets | Qt 6.12.0
Description: The QItemDelegate class provides display and editing facilities for data items from a model.
Keywords: class

- Qt 6.12
- Qt Widgets
- C++ Classes
- QItemDelegate
- Qt 6.12.0 Reference Documentation

# QItemDelegate Class

The QItemDelegate class provides display and editing facilities for data items from a model. More...

Header: | `#include <QItemDelegate>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Widgets)` `target_link_libraries(mytarget PRIVATE Qt6::Widgets)`
qmake: | `QT += widgets`
Inherits: | QAbstractItemDelegate

- List of all members, including inherited members

## Properties

- clipping : bool

## Public Functions

| QItemDelegate(QObject *parent = nullptr)
virtual | ~QItemDelegate()
bool | hasClipping() const
QItemEditorFactory * | itemEditorFactory() const
void | setClipping(bool clip)
void | setItemEditorFactory(QItemEditorFactory *factory)

## Reimplemented Public Functions

virtual QWidget * | createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const override
virtual void | paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const override
virtual void | setEditorData(QWidget *editor, const QModelIndex &index) const override
virtual void | setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const override
virtual QSize | sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const override
virtual void | updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const override

## Protected Functions

void | drawBackground(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const
virtual void | drawCheck(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, Qt::CheckState state) const
virtual void | drawDecoration(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, const QPixmap &pixmap) const
virtual void | drawDisplay(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, const QString &text) const
virtual void | drawFocus(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect) const

## Reimplemented Protected Functions

virtual bool | editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index) override
virtual bool | eventFilter(QObject *object, QEvent *event) override

## Detailed Description

QItemDelegate can be used to provide custom display features and editor widgets for item views based on QAbstractItemView subclasses. Using a delegate for this purpose allows the display and editing mechanisms to be customized and developed independently from the model and view.

The QItemDelegate class is one of the Model/View Classes and is part of Qt's model/view framework. Note that QStyledItemDelegate has taken over the job of drawing Qt's item views. We recommend the use of QStyledItemDelegate when creating new delegates.

When displaying items from a custom model in a standard view, it is often sufficient to simply ensure that the model returns appropriate data for each of the roles that determine the appearance of items in views. The default delegate used by Qt's standard views uses this role information to display items in most of the common forms expected by users. However, it is sometimes necessary to have even more control over the appearance of items than the default delegate can provide.

This class provides default implementations of the functions for painting item data in a view and editing data from item models. Default implementations of the paint() and sizeHint() virtual functions, defined in QAbstractItemDelegate, are provided to ensure that the delegate implements the correct basic behavior expected by views. You can reimplement these functions in subclasses to customize the appearance of items.

When editing data in an item view, QItemDelegate provides an editor widget, which is a widget that is placed on top of the view while editing takes place. Editors are created with a QItemEditorFactory; a default static instance provided by QItemEditorFactory is installed on all item delegates. You can set a custom factory using setItemEditorFactory() or set a new default factory with QItemEditorFactory::setDefaultFactory(). It is the data stored in the item model with the Qt::EditRole that is edited.

Only the standard editing functions for widget-based delegates are reimplemented here:

- createEditor() returns the widget used to change data from the model and can be reimplemented to customize editing behavior.
- setEditorData() provides the widget with data to manipulate.
- updateEditorGeometry() ensures that the editor is displayed correctly with respect to the item view.
- setModelData() returns updated data to the model.

The closeEditor() signal indicates that the user has completed editing the data, and that the editor widget can be destroyed.

### Standard Roles and Data Types

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.

Role | Accepted Types
--- | ---
Qt::BackgroundRole | QBrush
Qt::CheckStateRole | Qt::CheckState
Qt::DecorationRole | QIcon, QPixmap and QColor
Qt::DisplayRole | QString and types with a string representation
Qt::EditRole | See QItemEditorFactory for details
Qt::FontRole | QFont
Qt::SizeHintRole | QSize
Qt::TextAlignmentRole | Qt::Alignment
Qt::ForegroundRole | QBrush

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.

### Subclassing

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; such as 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 following code shows how a custom editor can be made available to delegates with the default item editor factory.

     QItemEditorFactory *editorFactory = new QItemEditorFactory;
     QItemEditorCreatorBase *creator = new QStandardItemEditorCreator<MyFancyDateTimeEdit>();
     editorFactory->registerEditor(QMetaType::QDateTime, creator);

     QItemEditorFactory::setDefaultFactory(editorFactory);

After the default factory has been set, all standard item delegates will use it (also the delegates that were created before setting the default factory).

This way, you can avoid subclassing QItemDelegate, and all values of the specified type (for example QMetaType::QDateTime) will be edited using the provided editor (like `MyFancyDateTimeEdit` in the above example).

An alternative is to reimplement createEditor(), setEditorData(), setModelData(), and updateEditorGeometry(). This process is described in the Model/View Programming overview documentation.

### QStyledItemDelegate vs. QItemDelegate

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, and QAbstractItemDelegate.

## Property Documentation

### clipping : bool

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)

## Member Function Documentation

### `[explicit]` QItemDelegate::QItemDelegate(QObject *parent = nullptr)

Constructs an item delegate with the given parent.

### `[virtual noexcept]` QItemDelegate::~QItemDelegate()

Destroys the item delegate.

### `[override virtual]` QWidget *QItemDelegate::createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const

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.

See also QAbstractItemDelegate::createEditor().

### `[protected]` void QItemDelegate::drawBackground(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const

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

### `[virtual protected]` void QItemDelegate::drawCheck(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, Qt::CheckState state) const

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

### `[virtual protected]` void QItemDelegate::drawDecoration(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, const QPixmap &pixmap) const

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

### `[virtual protected]` void QItemDelegate::drawDisplay(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect, const QString &text) const

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

### `[virtual protected]` void QItemDelegate::drawFocus(QPainter *painter, const QStyleOptionViewItem &option, const QRect &rect) const

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

### `[override virtual protected]` bool QItemDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)

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

### `[override virtual protected]` bool QItemDelegate::eventFilter(QObject *object, QEvent *event)

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

See details in QAbstractItemDelegate::handleEditorEvent().

### QItemEditorFactory *QItemDelegate::itemEditorFactory() const

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

See also setItemEditorFactory().

### `[override virtual]` void QItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const

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());

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.

See also QStyle::State.

### `[override virtual]` void QItemDelegate::setEditorData(QWidget *editor, const QModelIndex &index) const

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.

See also QMetaProperty::isUser().

### void QItemDelegate::setItemEditorFactory(QItemEditorFactory *factory)

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.

See also itemEditorFactory().

### `[override virtual]` void QItemDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const

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.

See also QMetaProperty::isUser().

### `[override virtual]` QSize QItemDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const

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.

### `[override virtual]` void QItemDelegate::updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const

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.