QSizePolicy Class

The QSizePolicy class is a layout attribute describing horizontal and vertical resizing policy. More...

Header:	#include <QSizePolicy>
CMake:	find_package(Qt6 COMPONENTS Widgets REQUIRED) target_link_libraries(mytarget PRIVATE Qt6::Widgets)
qmake:	QT += widgets

• List of all members, including inherited members

Public Types

enum	ControlType { DefaultType, ButtonBox, CheckBox, ComboBox, Frame, …, ToolButton }
flags	ControlTypes
enum	Policy { Fixed, Minimum, Maximum, Preferred, Expanding, …, Ignored }
enum	PolicyFlag { GrowFlag, ExpandFlag, ShrinkFlag, IgnoreFlag }

Public Functions

	QSizePolicy(QSizePolicy::Policy horizontal, QSizePolicy::Policy vertical, QSizePolicy::ControlType type = DefaultType)
	QSizePolicy()
QSizePolicy::ControlType	controlType() const
Qt::Orientations	expandingDirections() const
bool	hasHeightForWidth() const
bool	hasWidthForHeight() const
QSizePolicy::Policy	horizontalPolicy() const
int	horizontalStretch() const
bool	retainSizeWhenHidden() const
void	setControlType(QSizePolicy::ControlType type)
void	setHeightForWidth(bool dependent)
void	setHorizontalPolicy(QSizePolicy::Policy policy)
void	setHorizontalStretch(int stretchFactor)
void	setRetainSizeWhenHidden(bool retainSize)
void	setVerticalPolicy(QSizePolicy::Policy policy)
void	setVerticalStretch(int stretchFactor)
void	setWidthForHeight(bool dependent)
void	transpose()
QSizePolicy	transposed() const
QSizePolicy::Policy	verticalPolicy() const
int	verticalStretch() const
QVariant	operator QVariant() const
bool	operator!=(const QSizePolicy &other) const
bool	operator==(const QSizePolicy &other) const

Related Non-Members

size_t	qHash(QSizePolicy key, size_t seed = 0)
QDataStream &	operator<<(QDataStream &stream, const QSizePolicy &policy)
QDataStream &	operator>>(QDataStream &stream, QSizePolicy &policy)

Detailed Description

The size policy of a widget is an expression of its willingness to be resized in various ways, and affects how the widget is treated by the layout engine. Each widget returns a QSizePolicy that describes the horizontal and vertical resizing policy it prefers when being laid out. You can change this for a specific widget by changing its QWidget::sizePolicy property.

QSizePolicy contains two independent QSizePolicy::Policy values and two stretch factors; one describes the widgets's horizontal size policy, and the other describes its vertical size policy. It also contains a flag to indicate whether the height and width of its preferred size are related.

The horizontal and vertical policies can be set in the constructor, and altered using the setHorizontalPolicy() and setVerticalPolicy() functions. The stretch factors can be set using the setHorizontalStretch() and setVerticalStretch() functions. The flag indicating whether the widget's sizeHint() is width-dependent (such as a menu bar or a word-wrapping label) can be set using the setHeightForWidth() function.

The current size policies and stretch factors be retrieved using the horizontalPolicy(), verticalPolicy(), horizontalStretch() and verticalStretch() functions. Alternatively, use the transpose() function to swap the horizontal and vertical policies and stretches. The hasHeightForWidth() function returns the current status of the flag indicating the size hint dependencies.

Use the expandingDirections() function to determine whether the associated widget can make use of more space than its sizeHint() function indicates, as well as find out in which directions it can expand.

Finally, the QSizePolicy class provides operators comparing this size policy to a given policy, as well as a QVariant operator storing this QSizePolicy as a QVariant object.

See also QSize, QWidget::sizeHint(), QWidget::sizePolicy, and QLayoutItem::sizeHint().

Member Type Documentation

enum QSizePolicy::ControlTypeflags QSizePolicy::ControlTypes

This enum specifies the different types of widgets in terms of layout interaction:

Constant	Value	Description
QSizePolicy::DefaultType	0x00000001	The default type, when none is specified.
QSizePolicy::ButtonBox	0x00000002	A QDialogButtonBox instance.
QSizePolicy::CheckBox	0x00000004	A QCheckBox instance.
QSizePolicy::ComboBox	0x00000008	A QComboBox instance.
QSizePolicy::Frame	0x00000010	A QFrame instance.
QSizePolicy::GroupBox	0x00000020	A QGroupBox instance.
QSizePolicy::Label	0x00000040	A QLabel instance.
QSizePolicy::Line	0x00000080	A QFrame instance with QFrame::HLine or QFrame::VLine.
QSizePolicy::LineEdit	0x00000100	A QLineEdit instance.
QSizePolicy::PushButton	0x00000200	A QPushButton instance.
QSizePolicy::RadioButton	0x00000400	A QRadioButton instance.
QSizePolicy::Slider	0x00000800	A QAbstractSlider instance.
QSizePolicy::SpinBox	0x00001000	A QAbstractSpinBox instance.
QSizePolicy::TabWidget	0x00002000	A QTabWidget instance.
QSizePolicy::ToolButton	0x00004000	A QToolButton instance.

The ControlTypes type is a typedef for QFlags<ControlType>. It stores an OR combination of ControlType values.

See also setControlType() and controlType().

enum QSizePolicy::Policy

This enum describes the various per-dimension sizing types used when constructing a QSizePolicy.

Constant	Value	Description
QSizePolicy::Fixed	0	The QWidget::sizeHint() is the only acceptable alternative, so the widget can never grow or shrink (e.g. the vertical direction of a push button).
QSizePolicy::Minimum	GrowFlag	The sizeHint() is minimal, and sufficient. The widget can be expanded, but there is no advantage to it being larger (e.g. the horizontal direction of a push button). It cannot be smaller than the size provided by sizeHint().
QSizePolicy::Maximum	ShrinkFlag	The sizeHint() is a maximum. The widget can be shrunk any amount without detriment if other widgets need the space (e.g. a separator line). It cannot be larger than the size provided by sizeHint().
QSizePolicy::Preferred	GrowFlag | ShrinkFlag	The sizeHint() is best, but the widget can be shrunk and still be useful. The widget can be expanded, but there is no advantage to it being larger than sizeHint() (the default QWidget policy).
QSizePolicy::Expanding	GrowFlag | ShrinkFlag | ExpandFlag	The sizeHint() is a sensible size, but the widget can be shrunk and still be useful. The widget can make use of extra space, so it should get as much space as possible (e.g. the horizontal direction of a horizontal slider).
QSizePolicy::MinimumExpanding	GrowFlag | ExpandFlag	The sizeHint() is minimal, and sufficient. The widget can make use of extra space, so it should get as much space as possible (e.g. the horizontal direction of a horizontal slider).
QSizePolicy::Ignored	ShrinkFlag | GrowFlag | IgnoreFlag	The sizeHint() is ignored. The widget will get as much space as possible.

See also PolicyFlag, setHorizontalPolicy(), and setVerticalPolicy().

enum QSizePolicy::PolicyFlag

These flags are combined together to form the various Policy values:

Constant	Value	Description
QSizePolicy::GrowFlag	1	The widget can grow beyond its size hint if necessary.
QSizePolicy::ExpandFlag	2	The widget should get as much space as possible.
QSizePolicy::ShrinkFlag	4	The widget can shrink below its size hint if necessary.
QSizePolicy::IgnoreFlag	8	The widget's size hint is ignored. The widget will get as much space as possible.

See also Policy.

Member Function Documentation

QSizePolicy::QSizePolicy(QSizePolicy::Policy horizontal, QSizePolicy::Policy vertical, QSizePolicy::ControlType type = DefaultType)

Constructs a QSizePolicy object with the given horizontal and vertical policies, and the specified control type.

Use setHeightForWidth() if the preferred height of the widget is dependent on the width of the widget (for example, a QLabel with line wrapping).

See also setHorizontalStretch(), setVerticalStretch(), and controlType().

QSizePolicy::QSizePolicy()

Constructs a QSizePolicy object with Fixed as its horizontal and vertical policies.

The policies can be altered using the setHorizontalPolicy() and setVerticalPolicy() functions. Use the setHeightForWidth() function if the preferred height of the widget is dependent on the width of the widget (for example, a QLabel with line wrapping).

See also setHorizontalStretch() and setVerticalStretch().

QSizePolicy::ControlType QSizePolicy::controlType() const

Returns the control type associated with the widget for which this size policy applies.

See also setControlType().

Qt::Orientations QSizePolicy::expandingDirections() const

Returns whether a widget can make use of more space than the QWidget::sizeHint() function indicates.

A value of Qt::Horizontal or Qt::Vertical means that the widget can grow horizontally or vertically (i.e., the horizontal or vertical policy is Expanding or MinimumExpanding), whereas Qt::Horizontal | Qt::Vertical means that it can grow in both dimensions.

See also horizontalPolicy() and verticalPolicy().

bool QSizePolicy::hasHeightForWidth() const

Returns true if the widget's preferred height depends on its width; otherwise returns false.

See also setHeightForWidth().

bool QSizePolicy::hasWidthForHeight() const

Returns true if the widget's width depends on its height; otherwise returns false.

See also setWidthForHeight().

QSizePolicy::Policy QSizePolicy::horizontalPolicy() const

Returns the horizontal component of the size policy.

See also setHorizontalPolicy(), verticalPolicy(), and horizontalStretch().

int QSizePolicy::horizontalStretch() const

Returns the horizontal stretch factor of the size policy.

See also setHorizontalStretch(), verticalStretch(), and horizontalPolicy().

[since 5.2] bool QSizePolicy::retainSizeWhenHidden() const

Returns whether the layout should retain the widget's size when it is hidden. This is false by default.

This function was introduced in Qt 5.2.

See also setRetainSizeWhenHidden().

void QSizePolicy::setControlType(QSizePolicy::ControlType type)

Sets the control type associated with the widget for which this size policy applies to type.

The control type specifies the type of the widget for which this size policy applies. It is used by some styles, notably QMacStyle, to insert proper spacing between widgets. For example, the macOS Aqua guidelines specify that push buttons should be separated by 12 pixels, whereas vertically stacked radio buttons only require 6 pixels.

See also controlType() and QStyle::layoutSpacing().

void QSizePolicy::setHeightForWidth(bool dependent)

Sets the flag determining whether the widget's preferred height depends on its width, to dependent.

See also hasHeightForWidth() and setWidthForHeight().

void QSizePolicy::setHorizontalPolicy(QSizePolicy::Policy policy)

Sets the horizontal component to the given policy.

See also horizontalPolicy(), setVerticalPolicy(), and setHorizontalStretch().

void QSizePolicy::setHorizontalStretch(int stretchFactor)

Sets the horizontal stretch factor of the size policy to the given stretchFactor. stretchFactor must be in the range [0,255].

When two widgets are adjacent to each other in a horizontal layout, setting the horizontal stretch factor of the widget on the left to 2 and the factor of widget on the right to 1 will ensure that the widget on the left will always be twice the size of the one on the right.

See also horizontalStretch(), setVerticalStretch(), and setHorizontalPolicy().

[since 5.2] void QSizePolicy::setRetainSizeWhenHidden(bool retainSize)

Sets whether a layout should retain the widget's size when it is hidden. If retainSize is true, the layout will not be changed by hiding the widget.

This function was introduced in Qt 5.2.

See also retainSizeWhenHidden().

void QSizePolicy::setVerticalPolicy(QSizePolicy::Policy policy)

Sets the vertical component to the given policy.

See also verticalPolicy(), setHorizontalPolicy(), and setVerticalStretch().

void QSizePolicy::setVerticalStretch(int stretchFactor)

Sets the vertical stretch factor of the size policy to the given stretchFactor. stretchFactor must be in the range [0,255].

When two widgets are adjacent to each other in a vertical layout, setting the vertical stretch factor of the widget on the top to 2 and the factor of widget on the bottom to 1 will ensure that the widget on the top will always be twice the size of the one on the bottom.

See also verticalStretch(), setHorizontalStretch(), and setVerticalPolicy().

void QSizePolicy::setWidthForHeight(bool dependent)

Sets the flag determining whether the widget's width depends on its height, to dependent.

This is only supported for QGraphicsLayout's subclasses. It is not possible to have a layout with both height-for-width and width-for-height constraints at the same time.

See also hasWidthForHeight() and setHeightForWidth().

void QSizePolicy::transpose()

Swaps the horizontal and vertical policies and stretches.

See also transposed().

[since 5.9] QSizePolicy QSizePolicy::transposed() const

Returns a size policy object with the horizontal and vertical policies and stretches swapped.

This function was introduced in Qt 5.9.

See also transpose().

QSizePolicy::Policy QSizePolicy::verticalPolicy() const

Returns the vertical component of the size policy.

See also setVerticalPolicy(), horizontalPolicy(), and verticalStretch().

int QSizePolicy::verticalStretch() const

Returns the vertical stretch factor of the size policy.

See also setVerticalStretch(), horizontalStretch(), and verticalPolicy().

QVariant QSizePolicy::operator QVariant() const

Returns a QVariant storing this QSizePolicy.

bool QSizePolicy::operator!=(const QSizePolicy &other) const

Returns true if this policy is different from other; otherwise returns false.

See also operator==().

bool QSizePolicy::operator==(const QSizePolicy &other) const

Returns true if this policy is equal to other; otherwise returns false.

See also operator!=().