Detailed Description
The QStyledItemDelegate class provides display and editing facilities for data items from a model.
When displaying data from models in Qt item views, e.g., a QTableView, the individual items are drawn by a delegate. Also, when an item is edited, it provides an editor widget, which is placed on top of the item view while editing takes place. QStyledItemDelegate is the default delegate for all Qt item views, and is installed upon them when they are created.
The QStyledItemDelegate class is one of the Model/View Classes and is part of Qt's model/view framework. The delegate allows the display and editing of items to be developed independently from the model and view.
The data of items in models are assigned an ItemDataRole; each item can store a QVariant for each role. QStyledItemDelegate implements display and editing for the most common datatypes expected by users, including booleans, integers, and strings.
The data will be drawn differently depending on which role they have in the model. The following table describes the roles and the data types the delegate can handle for each of them. It is often sufficient to ensure that the model returns appropriate data for each of the roles to determine the appearance of items in views.
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 EditRole that is edited. See the QItemEditorFactory class for a more high-level introduction to item editor factories. The Color Editor Factory example shows how to create custom editors with a factory.
Subclassing QStyledItemDelegate
If the delegate does not support painting of the data types you need or you want to customize the drawing of items, you need to subclass QStyledItemDelegate, and reimplement paint() and possibly sizeHint(). The paint() function is called individually for each item, and with sizeHint(), you can specify the hint for each of them.
When reimplementing paint(), one would typically handle the datatypes one would like to draw and use the superclass implementation for other types.
The painting of check box indicators are performed by the current style. The style also specifies the size and the bounding rectangles in which to draw the data for the different data roles. The bounding rectangle of the item itself is also calculated by the style. When drawing already supported datatypes, it is therefore a good idea to ask the style for these bounding rectangles. The QStyle class description describes this in more detail.
If you wish to change any of the bounding rectangles calculated by the style or the painting of check box indicators, you can subclass QStyle. Note, however, that the size of the items can also be affected by reimplementing sizeHint().
It is possible for a custom delegate to provide editors without the use of an editor item factory. In this case, the following virtual functions must be reimplemented:
- 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 Star Delegate example creates editors by reimplementing these methods.
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.
If you wish to customize the painting of item views, you should implement a custom style. Please see the QStyle class documentation for details.
Member Function Documentation
QStyledItemDelegate::QStyledItemDelegate ( QObject * parent = 0 )
Constructs an item delegate with the given parent.
QStyledItemDelegate::~QStyledItemDelegate ()
Destroys the item delegate.
QWidget * QStyledItemDelegate::createEditor ( QWidget * parent, const QStyleOptionViewItem & option, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::createEditor().
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().
QString QStyledItemDelegate::displayText ( const QVariant & value, const QLocale & locale ) const [virtual]
This function returns the string that the delegate will use to display the Qt::DisplayRole of the model in locale. value is the value of the Qt::DisplayRole provided by the model.
The default implementation uses the QLocale::toString to convert value into a QString.
This function is not called for empty model indices, i.e., indices for which the model returns an invalid QVariant.
See also QAbstractItemModel::data().
bool QStyledItemDelegate::editorEvent ( QEvent * event, QAbstractItemModel * model, const QStyleOptionViewItem & option, const QModelIndex & index ) [virtual protected]
Reimplemented from QAbstractItemDelegate::editorEvent().
bool QStyledItemDelegate::eventFilter ( QObject * editor, QEvent * event ) [virtual protected]
Reimplemented from QObject::eventFilter().
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 comitted 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.
See also commitData() and closeEditor().
void QStyledItemDelegate::initStyleOption ( QStyleOptionViewItem * option, const QModelIndex & index ) const [virtual protected]
Initialize option with the values using the index index. This method is useful for subclasses when they need a QStyleOptionViewItem, but don't want to fill in all the information themselves. This function will check the version of the QStyleOptionViewItem and fill in the additional values for a QStyleOptionViewItemV2, QStyleOptionViewItemV3 and QStyleOptionViewItemV4.
See also QStyleOption::initFrom().
QItemEditorFactory * QStyledItemDelegate::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().
void QStyledItemDelegate::paint ( QPainter * painter, const QStyleOptionViewItem & option, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::paint().
Renders the delegate using the given painter and style option for the item specified by index.
This function paints the item using the view's QStyle.
When reimplementing paint in a subclass. Use the initStyleOption() to set up the option in the same way as the QStyledItemDelegate; the option will always be an instance of QStyleOptionViewItemV4. Please see its class description for information on its contents.
Whenever possible, use the option while painting. Especially its rect variable to decide where to draw and its state to determine if it is enabled or selected.
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 QItemDelegate::paint(), QStyle::drawControl(), and QStyle::CE_ItemViewItem.
void QStyledItemDelegate::setEditorData ( QWidget * editor, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::setEditorData().
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 QStyledItemDelegate::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().
void QStyledItemDelegate::setModelData ( QWidget * editor, QAbstractItemModel * model, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::setModelData().
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().
QSize QStyledItemDelegate::sizeHint ( const QStyleOptionViewItem & option, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::sizeHint().
Returns the size needed by the delegate to display the item specified by index, taking into account the style information provided by option.
This function uses the view's QStyle to determine the size of the item.
See also QStyle::sizeFromContents() and QStyle::CT_ItemViewItem.
void QStyledItemDelegate::updateEditorGeometry ( QWidget * editor, const QStyleOptionViewItem & option, const QModelIndex & index ) const [virtual]
Reimplemented from QAbstractItemDelegate::updateEditorGeometry().
Updates the editor for the item specified by index according to the style option given.
