QLayoutItem Class Reference

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

#include <qlayoutitem.h>

Inheritance diagram for QLayoutItem:

Public Functions
Qt::Alignment	alignment () const
	Returns the alignment of this item. More...
QSizePolicy::ControlTypes	controlTypes () const
	Returns the control type(s) for the layout item. More...
virtual Qt::Orientations	expandingDirections () const =0
	Returns whether this layout item can make use of more space than sizeHint(). More...
virtual QRect	geometry () const =0
	Returns the rectangle covered by this layout item. More...
virtual bool	hasHeightForWidth () const
	Returns true if this layout's preferred height depends on its width; otherwise returns false. More...
virtual int	heightForWidth (int) const
	Returns the preferred height for this layout item, given the width w. More...
virtual void	invalidate ()
	Invalidates any cached information in this layout item. More...
virtual bool	isEmpty () const =0
	Implemented in subclasses to return whether this item is empty, i. More...
virtual QLayout *	layout ()
	If this item is a QLayout, it is returned as a QLayout; otherwise 0 is returned. More...
virtual QSize	maximumSize () const =0
	Implemented in subclasses to return the maximum size of this item. More...
virtual int	minimumHeightForWidth (int) const
	Returns the minimum height this widget needs for the given width, w. More...
virtual QSize	minimumSize () const =0
	Implemented in subclasses to return the minimum size of this item. More...
	QLayoutItem (Qt::Alignment alignment=0)
	Constructs a layout item with an alignment. More...
void	setAlignment (Qt::Alignment a)
	Sets the alignment of this item to alignment. More...
virtual void	setGeometry (const QRect &)=0
	Implemented in subclasses to set this item's geometry to r. More...
virtual QSize	sizeHint () const =0
	Implemented in subclasses to return the preferred size of this item. More...
virtual QSpacerItem *	spacerItem ()
	If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise 0 is returned. More...
virtual QWidget *	widget ()
	If this item is a QWidget, it is returned as a QWidget; otherwise 0 is returned. More...
virtual	~QLayoutItem ()
	Destroys the QLayoutItem. More...

Protected Variables
Qt::Alignment	align

Detailed Description

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

This is used by custom layouts.

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

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 Trading Height for Width.

See also

QLayout

Definition at line 64 of file qlayoutitem.h.

Constructors and Destructors

QLayoutItem()

QLayoutItem::QLayoutItem ( Qt::Alignment  alignment = 0 )

inlineexplicit

Constructs a layout item with an alignment.

Not all subclasses support alignment.

Definition at line 93 of file qlayoutitem.h.

    : align(aalignment) { }

~QLayoutItem()

QLayoutItem::~QLayoutItem ( )

virtual

Destroys the QLayoutItem.

Definition at line 328 of file qlayoutitem.cpp.

{
}

Functions

alignment()

Qt::Alignment QLayoutItem::alignment ( ) const

inline

Returns the alignment of this item.

Definition at line 85 of file qlayoutitem.h.

Referenced by QGridLayout::maximumSize(), QBoxLayout::maximumSize(), setAlignment(), QFormLayout::setFormAlignment(), QBoxLayout::setGeometry(), QGridLayout::setGeometry(), and QFormLayout::setLabelAlignment().

{ return align; }

controlTypes()

QSizePolicy::ControlTypes QLayoutItem::controlTypes

(

)

const

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()

Definition at line 447 of file qlayoutitem.cpp.

Referenced by controlTypes(), QBoxLayoutPrivate::setupGeom(), and QGridLayoutPrivate::setupSpacings().

{
    // ### Qt 5: This function should probably be virtual instead
    if (const QWidget *widget = const_cast<QLayoutItem*>(this)->widget()) {
        return widget->sizePolicy().controlType();
    } else if (const QLayout *layout = const_cast<QLayoutItem*>(this)->layout()) {
        if (layout->count() == 0)
            return QSizePolicy::DefaultType;
        QSizePolicy::ControlTypes types;
        for (int i = layout->count() - 1; i >= 0; --i)
            types |= layout->itemAt(i)->controlTypes();
        return types;
    }
    return QSizePolicy::DefaultType;
}

expandingDirections()

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 QLayout, QFormLayout, QWidgetItem, QGridLayout, QBoxLayout, QSpacerItem, and QToolBarLayout.

Referenced by QDockAreaLayoutItem::expansive(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QBoxLayoutPrivate::setupGeom(), updateFormLayoutItem(), and QWizardPrivate::updateLayout().

geometry()

QRect QLayoutItem::geometry ( ) const

pure virtual

Returns the rectangle covered by this layout item.

See also

setGeometry()

Implemented in QLayout, QWidgetItem, and QSpacerItem.

Referenced by QBoxLayoutPrivate::effectiveMargins(), QGridLayoutPrivate::effectiveMargins(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QBoxLayoutPrivate::setupGeom(), and QGridLayoutPrivate::setupSpacings().

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 QFormLayout, QWidgetItem, QGridLayout, QBoxLayout, and QStackedLayoutHFW.

Definition at line 400 of file qlayoutitem.cpp.

Referenced by QWidgetPrivate::adjustedSize(), QLayout::closestAcceptableSize(), QWidgetPrivate::hasHeightForWidth(), QBoxLayoutItem::hfw(), QBoxLayoutItem::mhfw(), QtWndProc(), QWidgetItem::QWidgetItem(), QBoxLayout::setGeometry(), QWidgetItem::setGeometry(), QBoxLayoutPrivate::setupGeom(), updateFormLayoutItem(), QScrollAreaPrivate::updateScrollBars(), and QMessageBoxPrivate::updateSize().

{
    return false;
}

heightForWidth()

int QLayoutItem::heightForWidth ( int  ) const

virtual

Returns the preferred height for this layout item, given the width w.

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) {
        // not all C++ compilers support "mutable"
        MyLayout *that = (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 QWidgetItemV2, QFormLayout, QWidgetItem, QGridLayout, QBoxLayout, and QStackedLayoutHFW.

Definition at line 434 of file qlayoutitem.cpp.

Referenced by QBoxLayoutItem::hfw(), QBoxLayoutItem::mhfw(), minimumHeightForWidth(), QWidgetItem::QWidgetItem(), QBoxLayout::setGeometry(), and QWidgetItem::setGeometry().

{
    return -1;
}

invalidate()

void QLayoutItem::invalidate ( )

virtual

Invalidates any cached information in this layout item.

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

Definition at line 335 of file qlayoutitem.cpp.

Referenced by QLayout::activateRecursiveHelper().

{
}

isEmpty()

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, QWidgetItem, QSpacerItem, QToolBarLayout, and QToolBarItem.

Referenced by QDockAreaLayout::apply(), QWidgetItem::expandingDirections(), QDockAreaLayout::getGrid(), QWidgetItem::hasHeightForWidth(), QWidgetItem::heightForWidth(), QLayout::isEmpty(), QWidgetItem::maximumSize(), QWidgetItem::minimumSize(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QWidgetItem::setGeometry(), QBoxLayoutPrivate::setupGeom(), QWidgetItem::sizeHint(), QDockAreaLayoutItem::skip(), and QToolBarAreaLayoutItem::skip().

layout()

QLayout * QLayoutItem::layout ( )

virtual

If this item is a QLayout, it is returned as a QLayout; otherwise 0 is returned.

This function provides type-safe casting.

Reimplemented in QLayout.

Definition at line 343 of file qlayoutitem.cpp.

Referenced by QLayout::activateRecursiveHelper(), controlTypes(), QDockWidgetPrivate::endDrag(), QDockWidgetPrivate::init(), QDockWidgetPrivate::initDrag(), QDockWidget::initStyleOption(), QDockWidgetPrivate::mouseDoubleClickEvent(), QDockWidgetPrivate::mouseMoveEvent(), QDockWidgetPrivate::mousePressEvent(), QDockWidgetPrivate::moveEvent(), QDockWidgetPrivate::nonClientAreaMouseEvent(), QWizardPrivate::recreateLayout(), removeWidgetRecursively(), QLayoutPrivate::reparentChildWidgets(), QLayout::setAlignment(), QBoxLayout::setStretchFactor(), QDockWidgetPrivate::setWindowState(), QDockWidgetPrivate::startDrag(), QBoxLayout::takeAt(), QFormLayout::takeAt(), QGridLayoutPrivate::takeAt(), QDockWidgetPrivate::unplug(), QDockWidgetPrivate::updateButtons(), and QMenuBarPrivate::updateCornerWidgetToolBar().

{
    return 0;
}

maximumSize()

QSize QLayoutItem::maximumSize ( ) const

pure virtual

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

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

Referenced by QDockAreaLayoutItem::maximumSize(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QBoxLayout::setGeometry(), QWidgetItem::setGeometry(), QBoxLayoutPrivate::setupGeom(), QWidgetItemV2::updateCacheIfNecessary(), and updateFormLayoutItem().

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 QGridLayout, and QBoxLayout.

Definition at line 410 of file qlayoutitem.cpp.

Referenced by QLayout::closestAcceptableSize().

{
    return heightForWidth(w);
}

minimumSize()

QSize QLayoutItem::minimumSize ( ) const

pure virtual

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

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

Referenced by QDockAreaLayout::getGrid(), QBoxLayoutItem::mhfw(), QDockAreaLayoutItem::minimumSize(), QDockAreaLayout::minimumSize(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QBoxLayout::setGeometry(), QBoxLayoutPrivate::setupGeom(), QWidgetItemV2::updateCacheIfNecessary(), and updateFormLayoutItem().

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 207 of file qlayoutitem.cpp.

Referenced by QToolBarLayout::createItem(), QBoxLayout::insertWidget(), and QLayout::setAlignment().

{
    align = alignment;
}

setGeometry()

void QLayoutItem::setGeometry ( const QRect &  r )

pure virtual

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

See also

geometry()

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

Referenced by QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), and QBoxLayout::setGeometry().

sizeHint()

QSize QLayoutItem::sizeHint ( ) const

pure virtual

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

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

Referenced by QDockAreaLayout::getGrid(), QBoxLayoutItem::hfw(), QSpacerItem::QSpacerItem(), QWidgetItem::QWidgetItem(), QWidgetItem::setGeometry(), QBoxLayoutPrivate::setupGeom(), QDockAreaLayoutItem::sizeHint(), QDockAreaLayout::sizeHint(), QWidgetItemV2::updateCacheIfNecessary(), and updateFormLayoutItem().

spacerItem()

QSpacerItem * QLayoutItem::spacerItem ( )

virtual

If this item is a QSpacerItem, it is returned as a QSpacerItem; otherwise 0 is returned.

This function provides type-safe casting.

Reimplemented in QSpacerItem.

Definition at line 352 of file qlayoutitem.cpp.

Referenced by changeSpacerSize(), QSpacerItem::QSpacerItem(), QBoxLayout::setDirection(), and QComboBoxPrivateContainer::updateTopBottomMargin().

{
    return 0;
}

widget()

QWidget * QLayoutItem::widget ( )

virtual

If this item is a QWidget, it is returned as a QWidget; otherwise 0 is returned.

This function provides type-safe casting.

Reimplemented in QWidgetItem.

Definition at line 377 of file qlayoutitem.cpp.

Referenced by QGridLayoutPrivate::addData(), QStackedLayout::addItem(), QStackedLayout::addWidget(), QDockAreaLayoutInfo::apply(), QToolBarAreaLayout::apply(), QDockAreaLayout::apply(), QMainWindowLayoutState::centralWidget(), QMainWindowLayoutState::contains(), controlTypes(), QToolBarLayout::createItem(), QBoxLayoutPrivate::effectiveMargins(), QGridLayoutPrivate::effectiveMargins(), QToolBarAreaLayout::findToolBar(), QToolBarAreaLayoutLine::fitLayout(), fixToolBarOrientation(), QToolBarAreaLayout::getStyleOptionInfo(), QMainWindowLayout::hover(), QBoxLayoutItem::hStretch(), QLayout::indexOf(), QDockAreaLayoutInfo::indexOf(), QToolBarAreaLayout::indexOf(), QDockAreaLayoutInfo::info(), QDockAreaLayoutInfo::insertGap(), QMainWindowLayoutState::insertGap(), QToolBarAreaLayoutInfo::insertItem(), QToolBarAreaLayoutInfo::insertToolBarBreak(), QDialogButtonBoxPrivate::layoutButtons(), QDockAreaLayoutItem::maximumSize(), QStackedLayout::minimumSize(), QDockAreaLayoutItem::minimumSize(), QToolBarAreaLayoutInfo::moveToolBar(), QMainWindowLayout::plug(), QWidgetItem::QWidgetItem(), QToolBarAreaLayoutItem::realSizeHint(), QMainWindowLayoutState::remove(), QToolBarAreaLayoutInfo::removeToolBar(), QToolBarAreaLayoutInfo::removeToolBarBreak(), QLayout::removeWidget(), removeWidgetRecursively(), QLayoutPrivate::reparentChildWidgets(), QMainWindowLayout::revert(), QDockAreaLayoutInfo::saveState(), QAbstractScrollAreaScrollBarContainer::scrollBarLayoutIndex(), QLayout::setAlignment(), QWizardPrivate::setButtonLayout(), QStackedLayout::setCurrentIndex(), QStackedLayout::setGeometry(), QToolBar::setIconSize(), QDeclarativeView::setRootObject(), QStackedLayout::setStackingMode(), QBoxLayout::setStretchFactor(), QBoxLayoutPrivate::setupGeom(), QGridLayoutPrivate::setupSpacings(), QStackedLayout::sizeHint(), QDockAreaLayoutItem::sizeHint(), spacingHelper(), QMainWindowLayout::statusBar(), QDockAreaLayoutInfo::tab(), tabId(), QMainWindow::tabifiedDockWidgets(), QStackedLayout::takeAt(), QDockAreaLayoutInfo::takeAt(), QToolBarAreaLayout::toolBarBreak(), QDockAreaLayoutInfo::updateTabBar(), QBoxLayoutItem::vStretch(), QStackedWidget::widget(), QDockWidgetLayout::widgetForRole(), and QAbstractScrollAreaScrollBarContainer::widgets().

{
    return 0;
}

Properties

align

Qt::Alignment QLayoutItem::align

protected

Definition at line 90 of file qlayoutitem.h.

Referenced by QWidgetItem::expandingDirections(), QWidgetItem::maximumSize(), setAlignment(), QWidgetItem::setGeometry(), and QWidgetItemV2::updateCacheIfNecessary().

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

• /src/gui/kernel/qlayoutitem.h
• /src/gui/kernel/qlayoutitem.cpp