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QSizePolicy Class

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

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

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
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::ControlType
flags 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!=().

Related Non-Members

[since 5.6] size_t qHash(QSizePolicy key, size_t seed = 0)

Returns the hash value for key, using seed to seed the calculation.

This function was introduced in Qt 5.6.

QDataStream &operator<<(QDataStream &stream, const QSizePolicy &policy)

Writes the size policy to the data stream stream.

See also Format of the QDataStream operators.

QDataStream &operator>>(QDataStream &stream, QSizePolicy &policy)

Reads the size policy from the data stream stream.

See also Format of the QDataStream operators.

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