The QLayoutItem class provides an abstract item that a QLayout manipulates. More...

#include <qlayoutitem.h>

Inheritance diagram for QLayoutItem:

Collaboration diagram for QLayoutItem:

Public Member Functions
	QLayoutItem (Qt::Alignment alignment=Qt::Alignment())
	Constructs a layout item with an alignment.
virtual	~QLayoutItem ()
	Destroys the QLayoutItem.
virtual QSize	sizeHint () const =0
	Implemented in subclasses to return the preferred size of this item.
virtual QSize	minimumSize () const =0
	Implemented in subclasses to return the minimum size of this item.
virtual QSize	maximumSize () const =0
	Implemented in subclasses to return the maximum size of this item.
virtual Qt::Orientations	expandingDirections () const =0
	Returns whether this layout item can make use of more space than sizeHint().
virtual void	setGeometry (const QRect &)=0
	Implemented in subclasses to set this item's geometry to r.
virtual QRect	geometry () const =0
	Returns the rectangle covered by this layout item.
virtual bool	isEmpty () const =0
	Implemented in subclasses to return whether this item is empty, i.e.
virtual bool	hasHeightForWidth () const
	Returns `true` if this layout's preferred height depends on its width; otherwise returns `false`.
virtual int	heightForWidth (int) const
	Returns the preferred height for this layout item, given the width, which is not used in this default implementation.
virtual int	minimumHeightForWidth (int) const
	Returns the minimum height this widget needs for the given width, w.
virtual void	invalidate ()
	Invalidates any cached information in this layout item.
virtual QWidget *	widget () const
	If this item manages a QWidget, returns that widget.
virtual QLayout *	layout ()
	If this item is a QLayout, it is returned as a QLayout; otherwise \nullptr is returned.
virtual QSpacerItem *	spacerItem ()
	If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise \nullptr is returned.
Qt::Alignment	alignment () const
	Returns the alignment of this item.
void	setAlignment (Qt::Alignment a)
	Sets the alignment of this item to alignment.
virtual QSizePolicy::ControlTypes	controlTypes () const
	Returns the control type(s) for the layout item.

Protected Attributes
Qt::Alignment	align

Detailed Description

The QLayoutItem class provides an abstract item that a QLayout manipulates.

\inmodule QtWidgets

This is used by custom layouts.

Pure virtual functions are provided to return information about the layout, including, sizeHint(), minimumSize(), maximumSize() and expandingDirections().

The layout's geometry can be set and retrieved with setGeometry() and geometry(), and its alignment with setAlignment() and alignment().

isEmpty() returns whether the layout item is empty. If the concrete item is a QWidget, it can be retrieved using widget(). Similarly for layout() and spacerItem().

Some layouts have width and height interdependencies. These can be expressed using hasHeightForWidth(), heightForWidth(), and minimumHeightForWidth(). For more explanation see the {Qt Quarterly} article \l{http://doc.qt.io/archives/qq/qq04-height-for-width.html}{Trading Height for Width}.

See also: QLayout

Definition at line 25 of file qlayoutitem.h.

Constructor & Destructor Documentation

◆ QLayoutItem()

QLayoutItem::QLayoutItem ( Qt::Alignment alignment = Qt::Alignment() )

inlineexplicit

Constructs a layout item with an alignment.

Not all subclasses support alignment.

Definition at line 54 of file qlayoutitem.h.

◆ ~QLayoutItem()

QLayoutItem::~QLayoutItem ( )

virtualdefault

Destroys the QLayoutItem.

Member Function Documentation

◆ alignment()

Qt::Alignment QLayoutItem::alignment ( ) const

inline

Returns the alignment of this item.

Definition at line 46 of file qlayoutitem.h.

◆ controlTypes()

QSizePolicy::ControlTypes QLayoutItem::controlTypes ( ) const

virtual

Returns the control type(s) for the layout item.

For a QWidgetItem, the control type comes from the widget's size policy; for a QLayoutItem, the control types is derived from the layout's contents.

See also: QSizePolicy::controlType()

Reimplemented in QLayout, and QWidgetItem.

Definition at line 392 of file qlayoutitem.cpp.

◆ expandingDirections()

virtual Qt::Orientations QLayoutItem::expandingDirections ( ) const

pure virtual

Returns whether this layout item can make use of more space than sizeHint().

A value of Qt::Vertical or Qt::Horizontal means that it wants to grow in only one dimension, whereas Qt::Vertical | Qt::Horizontal means that it wants to grow in both dimensions.

Implemented in QBoxLayout, qdesigner_internal::PaddingSpacerItem, qdesigner_internal::PaddingSpacerItem, QFormLayout, QGridLayout, QLayout, QSpacerItem, QToolBarLayout, and QWidgetItem.

◆ geometry()

virtual QRect QLayoutItem::geometry ( ) const

pure virtual

Returns the rectangle covered by this layout item.

See also: setGeometry()

Implemented in QLayout, QSpacerItem, and QWidgetItem.

◆ hasHeightForWidth()

bool QLayoutItem::hasHeightForWidth ( ) const

virtual

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

The default implementation returns false.

Reimplement this function in layout managers that support height for width.

See also: heightForWidth(), QWidget::heightForWidth()

Reimplemented in QBoxLayout, QFormLayout, QGridLayout, QStackedLayout, and QWidgetItem.

Definition at line 345 of file qlayoutitem.cpp.

◆ heightForWidth()

int QLayoutItem::heightForWidth ( int ) const

virtual

Returns the preferred height for this layout item, given the width, which is not used in this default implementation.

The default implementation returns -1, indicating that the preferred height is independent of the width of the item. Using the function hasHeightForWidth() will typically be much faster than calling this function and testing for -1.

Reimplement this function in layout managers that support height for width. A typical implementation will look like this:

int MyLayout::heightForWidth(int w) const
{
    if (cache_dirty || cached_width != w) {
        MyLayout *that = const_cast<MyLayout *>(this);
        int h = calculateHeightForWidth(w);
        that->cached_hfw = h;
        return h;
    }
    return cached_hfw;
}

Caching is strongly recommended; without it layout will take exponential time.

See also: hasHeightForWidth()

Reimplemented in QBoxLayout, QFormLayout, QGridLayout, QStackedLayout, QWidgetItem, and QWidgetItemV2.

Definition at line 379 of file qlayoutitem.cpp.

◆ invalidate()

void QLayoutItem::invalidate ( )

virtual

Invalidates any cached information in this layout item.

Reimplemented in QBoxLayout, QFormLayout, QGridLayout, QLayout, QMainWindowLayout, and QToolBarLayout.

Definition at line 263 of file qlayoutitem.cpp.

◆ isEmpty()

virtual bool QLayoutItem::isEmpty ( ) const

pure virtual

Implemented in subclasses to return whether this item is empty, i.e.

whether it contains any widgets.

Implemented in QLayout, QSpacerItem, QToolBarItem, QToolBarLayout, and QWidgetItem.

◆ layout()

QLayout * QLayoutItem::layout ( )

virtual

If this item is a QLayout, it is returned as a QLayout; otherwise \nullptr is returned.

This function provides type-safe casting.

See also: spacerItem(), widget()

Reimplemented in QLayout.

Definition at line 273 of file qlayoutitem.cpp.

◆ maximumSize()

virtual QSize QLayoutItem::maximumSize ( ) const

pure virtual

Implemented in subclasses to return the maximum size of this item.

Implemented in QBoxLayout, QDockWidgetItem, QDockWidgetLayout, QGridLayout, QLayout, QSpacerItem, QWidgetItem, and QWidgetItemV2.

◆ minimumHeightForWidth()

int QLayoutItem::minimumHeightForWidth ( int w ) const

virtual

Returns the minimum height this widget needs for the given width, w.

The default implementation simply returns heightForWidth(w).

Reimplemented in QBoxLayout, QGridLayout, and QWidgetItem.

Definition at line 355 of file qlayoutitem.cpp.

◆ minimumSize()

virtual QSize QLayoutItem::minimumSize ( ) const

pure virtual

Implemented in subclasses to return the minimum size of this item.

Implemented in CardLayout, CardLayout, QBoxLayout, qdesigner_internal::QDesignerWidgetItem, QDockWidgetItem, QDockWidgetLayout, QFormLayout, QGridLayout, QLayout, QMainWindowLayout, QSpacerItem, QStackedLayout, QToolBarLayout, QWidgetItem, and QWidgetItemV2.

◆ setAlignment()

void QLayoutItem::setAlignment ( Qt::Alignment alignment )

Sets the alignment of this item to alignment.

{Note:} Item alignment is only supported by QLayoutItem subclasses where it would have a visual effect. Except for QSpacerItem, which provides blank space for layouts, all public Qt classes that inherit QLayoutItem support item alignment.

Definition at line 151 of file qlayoutitem.cpp.

◆ setGeometry()

virtual void QLayoutItem::setGeometry ( const QRect & r )

pure virtual

Implemented in subclasses to set this item's geometry to r.

See also: geometry()

Implemented in CardLayout, CardLayout, QBoxLayout, QDockWidgetLayout, QFormLayout, QGridLayout, QLayout, QMainWindowLayout, QSpacerItem, QStackedLayout, QToolBarLayout, and QWidgetItem.

◆ sizeHint()

virtual QSize QLayoutItem::sizeHint ( ) const

pure virtual

Implemented in subclasses to return the preferred size of this item.

Implemented in CardLayout, CardLayout, QBoxLayout, qdesigner_internal::QDesignerWidgetItem, QDockWidgetItem, QDockWidgetLayout, QFormLayout, QGridLayout, QMainWindowLayout, QSpacerItem, QStackedLayout, QToolBarLayout, QWidgetItem, and QWidgetItemV2.

◆ spacerItem()

QSpacerItem * QLayoutItem::spacerItem ( )

virtual

If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise \nullptr is returned.

This function provides type-safe casting.

See also: layout(), widget()

Reimplemented in QSpacerItem.

Definition at line 284 of file qlayoutitem.cpp.

◆ widget()

QWidget * QLayoutItem::widget ( ) const

virtual

If this item manages a QWidget, returns that widget.

Otherwise, \nullptr is returned.

Note: While the functions layout() and spacerItem() perform casts, this function returns another object: QLayout and QSpacerItem inherit QLayoutItem, while QWidget does not.

See also: layout(), spacerItem()

Reimplemented in QWidgetItem.

Definition at line 322 of file qlayoutitem.cpp.

Member Data Documentation

◆ align

Qt::Alignment QLayoutItem::align

protected

Definition at line 51 of file qlayoutitem.h.

The documentation for this class was generated from the following files:

qtbase/src/widgets/kernel/qlayoutitem.h (8825bcdbdab5f37b185261d7ba06260dc8e9930d)
qtbase/src/widgets/kernel/qlayoutitem.cpp (8825bcdbdab5f37b185261d7ba06260dc8e9930d)

Public Member Functions

Protected Attributes

Detailed Description

Constructor & Destructor Documentation

◆ QLayoutItem()

◆ ~QLayoutItem()

Member Function Documentation

◆ alignment()

◆ controlTypes()

◆ expandingDirections()

◆ geometry()

◆ hasHeightForWidth()

◆ heightForWidth()

◆ invalidate()

◆ isEmpty()

◆ layout()

◆ maximumSize()

◆ minimumHeightForWidth()

◆ minimumSize()

◆ setAlignment()

◆ setGeometry()

◆ sizeHint()

◆ spacerItem()

◆ widget()

Member Data Documentation

◆ align