QAbstractItemDelegate Class

The QAbstractItemDelegate class is used to display and edit data items from a model. More...

Header:	#include <QAbstractItemDelegate>
qmake:	QT += widgets
Inherits:	QObject
Inherited By:	QItemDelegate and QStyledItemDelegate

• List of all members, including inherited members

Public Types

enum	EndEditHint { NoHint, EditNextItem, EditPreviousItem, SubmitModelCache, RevertModelCache }

Public Functions

	QAbstractItemDelegate(QObject *parent = nullptr)
virtual	~QAbstractItemDelegate()
virtual QWidget *	createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const
virtual void	destroyEditor(QWidget *editor, const QModelIndex &index) const
virtual bool	editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)
virtual bool	helpEvent(QHelpEvent *event, QAbstractItemView *view, const QStyleOptionViewItem &option, const QModelIndex &index)
virtual void	paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const = 0
virtual void	setEditorData(QWidget *editor, const QModelIndex &index) const
virtual void	setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const
virtual QSize	sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const = 0
virtual void	updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const

Signals

void	closeEditor(QWidget *editor, QAbstractItemDelegate::EndEditHint hint = NoHint)
void	commitData(QWidget *editor)
void	sizeHintChanged(const QModelIndex &index)

Detailed Description

A QAbstractItemDelegate provides the interface and common functionality for delegates in the model/view architecture. Delegates display individual items in views, and handle the editing of model data.

The QAbstractItemDelegate class is one of the Model/View Classes and is part of Qt's model/view framework.

To render an item in a custom way, you must implement paint() and sizeHint(). The QStyledItemDelegate class provides default implementations for these functions; if you do not need custom rendering, subclass that class instead.

We give an example of drawing a progress bar in items; in our case for a package management program.

We create the WidgetDelegate class, which inherits from QStyledItemDelegate. We do the drawing in the paint() function:

void WidgetDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
                           const QModelIndex &index) const
{
    if (index.column() == 1) {
        int progress = index.data().toInt();

        QStyleOptionProgressBar progressBarOption;
        progressBarOption.rect = option.rect;
        progressBarOption.minimum = 0;
        progressBarOption.maximum = 100;
        progressBarOption.progress = progress;
        progressBarOption.text = QString::number(progress) + "%";
        progressBarOption.textVisible = true;

        QApplication::style()->drawControl(QStyle::CE_ProgressBar,
                                           &progressBarOption, painter);
    } else
        QStyledItemDelegate::paint(painter, option, index);

Notice that we use a QStyleOptionProgressBar and initialize its members. We can then use the current QStyle to draw it.

To provide custom editing, there are two approaches that can be used. The first approach is to create an editor widget and display it directly on top of the item. To do this you must reimplement createEditor() to provide an editor widget, setEditorData() to populate the editor with the data from the model, and setModelData() so that the delegate can update the model with data from the editor.

The second approach is to handle user events directly by reimplementing editorEvent().

See also Model/View Programming, QStyledItemDelegate, Pixelator Example, QStyledItemDelegate, and QStyle.

Member Type Documentation

enum QAbstractItemDelegate::EndEditHint

This enum describes the different hints that the delegate can give to the model and view components to make editing data in a model a comfortable experience for the user.

Constant	Value	Description
QAbstractItemDelegate::NoHint	0	There is no recommended action to be performed.

These hints let the delegate influence the behavior of the view:

Constant	Value	Description
QAbstractItemDelegate::EditNextItem	1	The view should use the delegate to open an editor on the next item in the view.
QAbstractItemDelegate::EditPreviousItem	2	The view should use the delegate to open an editor on the previous item in the view.

Note that custom views may interpret the concepts of next and previous differently.

The following hints are most useful when models are used that cache data, such as those that manipulate data locally in order to increase performance or conserve network bandwidth.

Constant	Value	Description
QAbstractItemDelegate::SubmitModelCache	3	If the model caches data, it should write out cached data to the underlying data store.
QAbstractItemDelegate::RevertModelCache	4	If the model caches data, it should discard cached data and replace it with data from the underlying data store.

Although models and views should respond to these hints in appropriate ways, custom components may ignore any or all of them if they are not relevant.

Member Function Documentation

QAbstractItemDelegate::QAbstractItemDelegate(QObject *parent = nullptr)

Creates a new abstract item delegate with the given parent.

[signal] void QAbstractItemDelegate::closeEditor(QWidget *editor, QAbstractItemDelegate::EndEditHint hint = NoHint)

This signal is emitted when the user has finished editing an item using the specified editor.

The hint provides a way for the delegate to influence how the model and view behave after editing is completed. It indicates to these components what action should be performed next to provide a comfortable editing experience for the user. For example, if EditNextItem is specified, the view should use a delegate to open an editor on the next item in the model.

See also EndEditHint.

[signal] void QAbstractItemDelegate::commitData(QWidget *editor)

This signal must be emitted when the editor widget has completed editing the data, and wants to write it back into the model.

[signal] void QAbstractItemDelegate::sizeHintChanged(const QModelIndex &index)

This signal must be emitted when the sizeHint() of index changed.

Views automatically connect to this signal and relayout items as necessary.

This function was introduced in Qt 4.4.

[virtual] QAbstractItemDelegate::~QAbstractItemDelegate()

Destroys the abstract item delegate.

[virtual] QWidget *QAbstractItemDelegate::createEditor(QWidget *parent, const QStyleOptionViewItem &option, const QModelIndex &index) const

Returns the editor to be used for editing the data item with the given index. Note that the index contains information about the model being used. The editor's parent widget is specified by parent, and the item options by option.

The base implementation returns nullptr. If you want custom editing you will need to reimplement this function.

The returned editor widget should have Qt::StrongFocus; otherwise, QMouseEvents received by the widget will propagate to the view. The view's background will shine through unless the editor paints its own background (e.g., with setAutoFillBackground()).

See also destroyEditor(), setModelData(), and setEditorData().

[virtual] void QAbstractItemDelegate::destroyEditor(QWidget *editor, const QModelIndex &index) const

Called when the editor is no longer needed for editing the data item with the given index and should be destroyed. The default behavior is a call to deleteLater on the editor. It is possible e.g. to avoid this delete by reimplementing this function.

This function was introduced in Qt 5.0.

See also createEditor().

[virtual] bool QAbstractItemDelegate::editorEvent(QEvent *event, QAbstractItemModel *model, const QStyleOptionViewItem &option, const QModelIndex &index)

When editing of an item starts, this function is called with the event that triggered the editing, the model, the index of the item, and the option used for rendering the item.

Mouse events are sent to editorEvent() even if they don't start editing of the item. This can, for instance, be useful if you wish to open a context menu when the right mouse button is pressed on an item.

The base implementation returns false (indicating that it has not handled the event).

[virtual] bool QAbstractItemDelegate::helpEvent(QHelpEvent *event, QAbstractItemView *view, const QStyleOptionViewItem &option, const QModelIndex &index)

Whenever a help event occurs, this function is called with the event view option and the index that corresponds to the item where the event occurs.

Returns true if the delegate can handle the event; otherwise returns false. A return value of true indicates that the data obtained using the index had the required role.

For QEvent::ToolTip and QEvent::WhatsThis events that were handled successfully, the relevant popup may be shown depending on the user's system configuration.

This function was introduced in Qt 4.3.

See also QHelpEvent.

[pure virtual] void QAbstractItemDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option, const QModelIndex &index) const

This pure abstract function must be reimplemented if you want to provide custom rendering. Use the painter and style option to render the item specified by the item index.

If you reimplement this you must also reimplement sizeHint().

[virtual] void QAbstractItemDelegate::setEditorData(QWidget *editor, const QModelIndex &index) const

Sets the contents of the given editor to the data for the item at the given index. Note that the index contains information about the model being used.

The base implementation does nothing. If you want custom editing you will need to reimplement this function.

See also setModelData().

[virtual] void QAbstractItemDelegate::setModelData(QWidget *editor, QAbstractItemModel *model, const QModelIndex &index) const

Sets the data for the item at the given index in the model to the contents of the given editor.

The base implementation does nothing. If you want custom editing you will need to reimplement this function.

See also setEditorData().

[pure virtual] QSize QAbstractItemDelegate::sizeHint(const QStyleOptionViewItem &option, const QModelIndex &index) const

This pure abstract function must be reimplemented if you want to provide custom rendering. The options are specified by option and the model item by index.

If you reimplement this you must also reimplement paint().

[virtual] void QAbstractItemDelegate::updateEditorGeometry(QWidget *editor, const QStyleOptionViewItem &option, const QModelIndex &index) const

Updates the geometry of the editor for the item with the given index, according to the rectangle specified in the option. If the item has an internal layout, the editor will be laid out accordingly. Note that the index contains information about the model being used.

The base implementation does nothing. If you want custom editing you must reimplement this function.