- Qt 6.9
- Qt GUI
- C++ Classes
- QAbstractTextDocumentLayout
- Qt 6.9.3 Reference Documentation

# QAbstractTextDocumentLayout Class

The QAbstractTextDocumentLayout class is an abstract base class used to implement custom layouts for QTextDocuments. More...

Header: | `#include <QAbstractTextDocumentLayout>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Gui)` `target_link_libraries(mytarget PRIVATE Qt6::Gui)`
qmake: | `QT += gui`
Inherits: | QObject
Inherited By: | QPlainTextDocumentLayout

- List of all members, including inherited members
- QAbstractTextDocumentLayout is part of Rich Text Processing APIs.

Note: All functions in this class are reentrant.

## Public Types

struct | PaintContext
struct | Selection

## Public Functions

| QAbstractTextDocumentLayout(QTextDocument *document)
QString | anchorAt(const QPointF &position) const
virtual QRectF | blockBoundingRect(const QTextBlock &block) const = 0
QTextBlock | blockWithMarkerAt(const QPointF &pos) const
QTextDocument * | document() const
virtual QSizeF | documentSize() const = 0
virtual void | draw(QPainter *painter, const QAbstractTextDocumentLayout::PaintContext &context) = 0
QTextFormat | formatAt(const QPointF &pos) const
virtual QRectF | frameBoundingRect(QTextFrame *frame) const = 0
QTextObjectInterface * | handlerForObject(int objectType) const
virtual int | hitTest(const QPointF &point, Qt::HitTestAccuracy accuracy) const = 0
QString | imageAt(const QPointF &pos) const
virtual int | pageCount() const = 0
QPaintDevice * | paintDevice() const
void | registerHandler(int objectType, QObject *component)
void | setPaintDevice(QPaintDevice *device)
void | unregisterHandler(int objectType, QObject *component = nullptr)

## Signals

void | documentSizeChanged(const QSizeF &newSize)
void | pageCountChanged(int newPages)
void | update(const QRectF &rect = QRectF(0., 0., 1000000000., 1000000000.))
void | updateBlock(const QTextBlock &block)

## Protected Functions

virtual void | documentChanged(int position, int charsRemoved, int charsAdded) = 0
virtual void | drawInlineObject(QPainter *painter, const QRectF &rect, QTextInlineObject object, int posInDocument, const QTextFormat &format)
QTextCharFormat | format(int position)
virtual void | positionInlineObject(QTextInlineObject item, int posInDocument, const QTextFormat &format)
virtual void | resizeInlineObject(QTextInlineObject item, int posInDocument, const QTextFormat &format)

## Detailed Description

The standard layout provided by Qt can handle simple word processing including inline images, lists and tables.

Some applications, e.g., a word processor or a DTP application might need more features than the ones provided by Qt's layout engine, in which case you can subclass QAbstractTextDocumentLayout to provide custom layout behavior for your text documents.

An instance of the QAbstractTextDocumentLayout subclass can be installed on a QTextDocument object with the setDocumentLayout() function.

You can insert custom objects into a QTextDocument; see the QTextObjectInterface class description for details.

See also QTextObjectInterface.

## Member Function Documentation

### `[explicit]` QAbstractTextDocumentLayout::QAbstractTextDocumentLayout(QTextDocument *document)

Creates a new text document layout for the given document.

### QString QAbstractTextDocumentLayout::anchorAt(const QPointF &position) const

Returns the reference of the anchor the given position, or an empty string if no anchor exists at that point.

### `[pure virtual]` QRectF QAbstractTextDocumentLayout::blockBoundingRect(const QTextBlock &block) const

Returns the bounding rectangle of block.

### QTextBlock QAbstractTextDocumentLayout::blockWithMarkerAt(const QPointF &pos) const

Returns the block (probably a list item) whose marker is found at the given position pos.

### QTextDocument *QAbstractTextDocumentLayout::document() const

Returns the text document that this layout is operating on.

### `[pure virtual protected]` void QAbstractTextDocumentLayout::documentChanged(int position, int charsRemoved, int charsAdded)

This function is called whenever the contents of the document change. A change occurs when text is inserted, removed, or a combination of these two. The change is specified by position, charsRemoved, and charsAdded corresponding to the starting character position of the change, the number of characters removed from the document, and the number of characters added.

For example, when inserting the text "Hello" into an empty document, charsRemoved would be 0 and charsAdded would be 5 (the length of the string).

Replacing text is a combination of removing and inserting. For example, if the text "Hello" gets replaced by "Hi", charsRemoved would be 5 and charsAdded would be 2.

For subclasses of QAbstractTextDocumentLayout, this is the central function where a large portion of the work to lay out and position document contents is done.

For example, in a subclass that only arranges blocks of text, an implementation of this function would have to do the following:

- Determine the list of changed QTextBlock(s) using the parameters provided.
- Each QTextBlock object's corresponding QTextLayout object needs to be processed. You can access the QTextBlock's layout using the QTextBlock::layout() function. This processing should take the document's page size into consideration.
- If the total number of pages changed, the pageCountChanged() signal should be emitted.
- If the total size changed, the documentSizeChanged() signal should be emitted.
- The update() signal should be emitted to schedule a repaint of areas in the layout that require repainting.

See also QTextLayout.

### `[pure virtual]` QSizeF QAbstractTextDocumentLayout::documentSize() const

Returns the total size of the document's layout.

This information can be used by display widgets to update their scroll bars correctly.

See also documentSizeChanged() and QTextDocument::pageSize.

### `[signal]` void QAbstractTextDocumentLayout::documentSizeChanged(const QSizeF &newSize)

This signal is emitted when the size of the document layout changes to newSize.

Subclasses of QAbstractTextDocumentLayout should emit this signal when the document's entire layout size changes. This signal is useful for widgets that display text documents since it enables them to update their scroll bars correctly.

See also documentSize().

### `[pure virtual]` void QAbstractTextDocumentLayout::draw(QPainter *painter, const QAbstractTextDocumentLayout::PaintContext &context)

Draws the layout with the given painter using the given context.

### `[virtual protected]` void QAbstractTextDocumentLayout::drawInlineObject(QPainter *painter, const QRectF &rect, QTextInlineObject object, int posInDocument, const QTextFormat &format)

This function is called to draw the inline object, object, with the given painter within the rectangle specified by rect using the specified text format.

posInDocument specifies the position of the object within the document.

The default implementation calls drawObject() on the object handlers. This function is called only within Qt. Subclasses can reimplement this function to customize the drawing of inline objects.

See also draw().

### `[protected]` QTextCharFormat QAbstractTextDocumentLayout::format(int position)

Returns the character format that is applicable at the given position.

### QTextFormat QAbstractTextDocumentLayout::formatAt(const QPointF &pos) const

Returns the text format at the given position pos.

### `[pure virtual]` QRectF QAbstractTextDocumentLayout::frameBoundingRect(QTextFrame *frame) const

Returns the bounding rectangle of frame.

### QTextObjectInterface *QAbstractTextDocumentLayout::handlerForObject(int objectType) const

Returns a handler for objects of the given objectType.

### `[pure virtual]` int QAbstractTextDocumentLayout::hitTest(const QPointF &point, Qt::HitTestAccuracy accuracy) const

Returns the cursor position for the given point with the specified accuracy. Returns -1 if no valid cursor position was found.

### QString QAbstractTextDocumentLayout::imageAt(const QPointF &pos) const

Returns the source of the image at the given position pos, or an empty string if no image exists at that point.

### `[pure virtual]` int QAbstractTextDocumentLayout::pageCount() const

Returns the number of pages contained in the layout.

See also pageCountChanged().

### `[signal]` void QAbstractTextDocumentLayout::pageCountChanged(int newPages)

This signal is emitted when the number of pages in the layout changes; newPages is the updated page count.

Subclasses of QAbstractTextDocumentLayout should emit this signal when the number of pages in the layout has changed. Changes to the page count are caused by changes to the layout or the document content itself.

See also pageCount().

### QPaintDevice *QAbstractTextDocumentLayout::paintDevice() const

Returns the paint device used to render the document's layout.

See also setPaintDevice().

### `[virtual protected]` void QAbstractTextDocumentLayout::positionInlineObject(QTextInlineObject item, int posInDocument, const QTextFormat &format)

Lays out the inline object item using the given text format.

posInDocument specifies the position of the object within the document.

The default implementation does nothing. This function is called only within Qt. Subclasses can reimplement this function to customize the position of inline objects.

See also drawInlineObject().

### void QAbstractTextDocumentLayout::registerHandler(int objectType, QObject *component)

Registers the given component as a handler for items of the given objectType.

Note: registerHandler() has to be called once for each object type. This means that there is only one handler for multiple replacement characters of the same object type.

The text document layout does not take ownership of `component`.

### `[virtual protected]` void QAbstractTextDocumentLayout::resizeInlineObject(QTextInlineObject item, int posInDocument, const QTextFormat &format)

Sets the size of the inline object item corresponding to the text format.

posInDocument specifies the position of the object within the document.

The default implementation resizes the item to the size returned by the object handler's intrinsicSize() function. This function is called only within Qt. Subclasses can reimplement this function to customize the resizing of inline objects.

### void QAbstractTextDocumentLayout::setPaintDevice(QPaintDevice *device)

Sets the paint device used for rendering the document's layout to the given device.

See also paintDevice().

### void QAbstractTextDocumentLayout::unregisterHandler(int objectType, QObject *component = nullptr)

Unregisters the given component as a handler for items of the given objectType, or any handler if the component is not specified.

### `[signal]` void QAbstractTextDocumentLayout::update(const QRectF &rect = QRectF(0., 0., 1000000000., 1000000000.))

This signal is emitted when the rectangle rect has been updated.

Subclasses of QAbstractTextDocumentLayout should emit this signal when the layout of the contents change in order to repaint.

### `[signal]` void QAbstractTextDocumentLayout::updateBlock(const QTextBlock &block)

This signal is emitted when the specified block has been updated.

Subclasses of QAbstractTextDocumentLayout should emit this signal when the layout of block has changed in order to repaint.