QBoxLayout Class

The QBoxLayout class lines up child widgets horizontally or vertically. More...

Header:	#include <QBoxLayout>
CMake:	find_package(Qt6 COMPONENTS Widgets REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Widgets)
qmake:	QT += widgets
Inherits:	QLayout
Inherited By:	QHBoxLayout and QVBoxLayout

• List of all members, including inherited members

Public Types

enum	Direction { LeftToRight, RightToLeft, TopToBottom, BottomToTop }

Public Functions

	QBoxLayout(QBoxLayout::Direction dir, QWidget *parent = nullptr)
virtual	~QBoxLayout()
void	addLayout(QLayout *layout, int stretch = 0)
void	addSpacerItem(QSpacerItem *spacerItem)
void	addSpacing(int size)
void	addStretch(int stretch = 0)
void	addStrut(int size)
void	addWidget(QWidget *widget, int stretch = 0, Qt::Alignment alignment = Qt::Alignment())
QBoxLayout::Direction	direction() const
void	insertItem(int index, QLayoutItem *item)
void	insertLayout(int index, QLayout *layout, int stretch = 0)
void	insertSpacerItem(int index, QSpacerItem *spacerItem)
void	insertSpacing(int index, int size)
void	insertStretch(int index, int stretch = 0)
void	insertWidget(int index, QWidget *widget, int stretch = 0, Qt::Alignment alignment = Qt::Alignment())
void	setDirection(QBoxLayout::Direction direction)
void	setStretch(int index, int stretch)
bool	setStretchFactor(QWidget *widget, int stretch)
bool	setStretchFactor(QLayout *layout, int stretch)
int	stretch(int index) const

Reimplemented Public Functions

virtual void	addItem(QLayoutItem *item) override
virtual int	count() const override
virtual Qt::Orientations	expandingDirections() const override
virtual bool	hasHeightForWidth() const override
virtual int	heightForWidth(int w) const override
virtual void	invalidate() override
virtual QLayoutItem *	itemAt(int index) const override
virtual QSize	maximumSize() const override
virtual int	minimumHeightForWidth(int w) const override
virtual QSize	minimumSize() const override
virtual void	setGeometry(const QRect &r) override
virtual void	setSpacing(int spacing) override
virtual QSize	sizeHint() const override
virtual int	spacing() const override
virtual QLayoutItem *	takeAt(int index) override

Detailed Description

QBoxLayout takes the space it gets (from its parent layout or from the parentWidget()), divides it up into a row of boxes, and makes each managed widget fill one box.

If the QBoxLayout's orientation is Qt::Horizontal the boxes are placed in a row, with suitable sizes. Each widget (or other box) will get at least its minimum size and at most its maximum size. Any excess space is shared according to the stretch factors (more about that below).

If the QBoxLayout's orientation is Qt::Vertical, the boxes are placed in a column, again with suitable sizes.

The easiest way to create a QBoxLayout is to use one of the convenience classes, e.g. QHBoxLayout (for Qt::Horizontal boxes) or QVBoxLayout (for Qt::Vertical boxes). You can also use the QBoxLayout constructor directly, specifying its direction as LeftToRight, RightToLeft, TopToBottom, or BottomToTop.

If the QBoxLayout is not the top-level layout (i.e. it is not managing all of the widget's area and children), you must add it to its parent layout before you can do anything with it. The normal way to add a layout is by calling parentLayout->addLayout().

Once you have done this, you can add boxes to the QBoxLayout using one of four functions:

• addWidget() to add a widget to the QBoxLayout and set the widget's stretch factor. (The stretch factor is along the row of boxes.)
• addSpacing() to create an empty box; this is one of the functions you use to create nice and spacious dialogs. See below for ways to set margins.
• addStretch() to create an empty, stretchable box.
• addLayout() to add a box containing another QLayout to the row and set that layout's stretch factor.

Use insertWidget(), insertSpacing(), insertStretch() or insertLayout() to insert a box at a specified position in the layout.

QBoxLayout also includes two margin widths:

• setContentsMargins() sets the width of the outer border on each side of the widget. This is the width of the reserved space along each of the QBoxLayout's four sides.
• setSpacing() sets the width between neighboring boxes. (You can use addSpacing() to get more space at a particular spot.)

The margin default is provided by the style. The default margin most Qt styles specify is 9 for child widgets and 11 for windows. The spacing defaults to the same as the margin width for a top-level layout, or to the same as the parent layout.

To remove a widget from a layout, call removeWidget(). Calling QWidget::hide() on a widget also effectively removes the widget from the layout until QWidget::show() is called.

You will almost always want to use QVBoxLayout and QHBoxLayout rather than QBoxLayout because of their convenient constructors.

See also QGridLayout, QStackedLayout, and Layout Management.

Member Type Documentation

enum QBoxLayout::Direction

This type is used to determine the direction of a box layout.

Constant	Value	Description
QBoxLayout::LeftToRight	0	Horizontal from left to right.
QBoxLayout::RightToLeft	1	Horizontal from right to left.
QBoxLayout::TopToBottom	2	Vertical from top to bottom.
QBoxLayout::BottomToTop	3	Vertical from bottom to top.

Member Function Documentation

QBoxLayout::QBoxLayout(QBoxLayout::Direction dir, QWidget *parent = nullptr)

Constructs a new QBoxLayout with direction dir and parent widget parent.

The layout is set directly as the top-level layout for parent. There can be only one top-level layout for a widget. It is returned by QWidget::layout().

See also direction() and QWidget::setLayout().

[virtual] QBoxLayout::~QBoxLayout()

Destroys this box layout.

The layout's widgets aren't destroyed.

[override virtual] void QBoxLayout::addItem(QLayoutItem *item)

Reimplements: QLayout::addItem(QLayoutItem *item).

void QBoxLayout::addLayout(QLayout *layout, int stretch = 0)

Adds layout to the end of the box, with serial stretch factor stretch.

See also insertLayout(), addItem(), and addWidget().

void QBoxLayout::addSpacerItem(QSpacerItem *spacerItem)

Adds spacerItem to the end of this box layout.

See also addSpacing() and addStretch().

void QBoxLayout::addSpacing(int size)

Adds a non-stretchable space (a QSpacerItem) with size size to the end of this box layout. QBoxLayout provides default margin and spacing. This function adds additional space.

See also insertSpacing(), addItem(), and QSpacerItem.

void QBoxLayout::addStretch(int stretch = 0)

Adds a stretchable space (a QSpacerItem) with zero minimum size and stretch factor stretch to the end of this box layout.

See also insertStretch(), addItem(), and QSpacerItem.

void QBoxLayout::addStrut(int size)

Limits the perpendicular dimension of the box (e.g. height if the box is LeftToRight) to a minimum of size. Other constraints may increase the limit.

See also addItem().

void QBoxLayout::addWidget(QWidget *widget, int stretch = 0, Qt::Alignment alignment = Qt::Alignment())

Adds widget to the end of this box layout, with a stretch factor of stretch and alignment alignment.

The stretch factor applies only in the direction of the QBoxLayout, and is relative to the other boxes and widgets in this QBoxLayout. Widgets and boxes with higher stretch factors grow more.

If the stretch factor is 0 and nothing else in the QBoxLayout has a stretch factor greater than zero, the space is distributed according to the QWidget:sizePolicy() of each widget that's involved.

The alignment is specified by alignment. The default alignment is 0, which means that the widget fills the entire cell.

See also insertWidget(), addItem(), addLayout(), addStretch(), addSpacing(), and addStrut().

[override virtual] int QBoxLayout::count() const

Reimplements: QLayout::count() const.

QBoxLayout::Direction QBoxLayout::direction() const

Returns the direction of the box. addWidget() and addSpacing() work in this direction; the stretch stretches in this direction.

See also setDirection(), QBoxLayout::Direction, addWidget(), and addSpacing().

[override virtual] Qt::Orientations QBoxLayout::expandingDirections() const

Reimplements: QLayout::expandingDirections() const.

[override virtual] bool QBoxLayout::hasHeightForWidth() const

Reimplements: QLayoutItem::hasHeightForWidth() const.

[override virtual] int QBoxLayout::heightForWidth(int w) const

Reimplements: QLayoutItem::heightForWidth(int) const.

void QBoxLayout::insertItem(int index, QLayoutItem *item)

Inserts item into this box layout at position index. If index is negative, the item is added at the end.

See also addItem(), insertWidget(), insertLayout(), insertStretch(), and insertSpacing().

void QBoxLayout::insertLayout(int index, QLayout *layout, int stretch = 0)

Inserts layout at position index, with stretch factor stretch. If index is negative, the layout is added at the end.

layout becomes a child of the box layout.

See also addLayout() and insertItem().

void QBoxLayout::insertSpacerItem(int index, QSpacerItem *spacerItem)

Inserts spacerItem at position index, with zero minimum size and stretch factor. If index is negative the space is added at the end.

See also addSpacerItem(), insertStretch(), and insertSpacing().

void QBoxLayout::insertSpacing(int index, int size)

Inserts a non-stretchable space (a QSpacerItem) at position index, with size size. If index is negative the space is added at the end.

The box layout has default margin and spacing. This function adds additional space.

See also addSpacing(), insertItem(), and QSpacerItem.

void QBoxLayout::insertStretch(int index, int stretch = 0)

Inserts a stretchable space (a QSpacerItem) at position index, with zero minimum size and stretch factor stretch. If index is negative the space is added at the end.

See also addStretch(), insertItem(), and QSpacerItem.

void QBoxLayout::insertWidget(int index, QWidget *widget, int stretch = 0, Qt::Alignment alignment = Qt::Alignment())

Inserts widget at position index, with stretch factor stretch and alignment alignment. If index is negative, the widget is added at the end.

The stretch factor applies only in the direction of the QBoxLayout, and is relative to the other boxes and widgets in this QBoxLayout. Widgets and boxes with higher stretch factors grow more.

If the stretch factor is 0 and nothing else in the QBoxLayout has a stretch factor greater than zero, the space is distributed according to the QWidget:sizePolicy() of each widget that's involved.

The alignment is specified by alignment. The default alignment is 0, which means that the widget fills the entire cell.

See also addWidget() and insertItem().

[override virtual] void QBoxLayout::invalidate()

Reimplements: QLayout::invalidate().

Resets cached information.

[override virtual] QLayoutItem *QBoxLayout::itemAt(int index) const

Reimplements: QLayout::itemAt(int index) const.

[override virtual] QSize QBoxLayout::maximumSize() const

Reimplements: QLayout::maximumSize() const.

[override virtual] int QBoxLayout::minimumHeightForWidth(int w) const

Reimplements: QLayoutItem::minimumHeightForWidth(int w) const.

[override virtual] QSize QBoxLayout::minimumSize() const

Reimplements: QLayout::minimumSize() const.

void QBoxLayout::setDirection(QBoxLayout::Direction direction)

Sets the direction of this layout to direction.

See also direction().

[override virtual] void QBoxLayout::setGeometry(const QRect &r)

Reimplements: QLayout::setGeometry(const QRect &r).

[override virtual] void QBoxLayout::setSpacing(int spacing)

Reimplements an access function for property: QLayout::spacing.

Reimplements QLayout::setSpacing(). Sets the spacing property to spacing.

See also QLayout::setSpacing() and spacing().

void QBoxLayout::setStretch(int index, int stretch)

Sets the stretch factor at position index. to stretch.

See also stretch().

bool QBoxLayout::setStretchFactor(QWidget *widget, int stretch)

Sets the stretch factor for widget to stretch and returns true if widget is found in this layout (not including child layouts); otherwise returns false.

See also setAlignment().

bool QBoxLayout::setStretchFactor(QLayout *layout, int stretch)

This is an overloaded function.

Sets the stretch factor for the layout layout to stretch and returns true if layout is found in this layout (not including child layouts); otherwise returns false.

[override virtual] QSize QBoxLayout::sizeHint() const

Reimplements: QLayoutItem::sizeHint() const.

[override virtual] int QBoxLayout::spacing() const

Reimplements an access function for property: QLayout::spacing.

Reimplements QLayout::spacing(). If the spacing property is valid, that value is returned. Otherwise, a value for the spacing property is computed and returned. Since layout spacing in a widget is style dependent, if the parent is a widget, it queries the style for the (horizontal or vertical) spacing of the layout. Otherwise, the parent is a layout, and it queries the parent layout for the spacing().

See also QLayout::spacing() and setSpacing().

int QBoxLayout::stretch(int index) const

Returns the stretch factor at position index.

See also setStretch().

[override virtual] QLayoutItem *QBoxLayout::takeAt(int index)

Reimplements: QLayout::takeAt(int index).