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QBoxLayout Class Reference

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

#include <QBoxLayout>

Inherits QLayout.

Inherited by QHBoxLayout and QVBoxLayout.

Public Types

Writable Properties

Public Functions

Public Slots

Signals

Static Public Members

Protected Functions


Detailed Description

The QBoxLayout class lines up child widgets horizontally or vertically.

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.

Qt::Horizontal box with five child widgets

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).

Qt::Vertical box with five child widgets

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, Down, RightToLeft or Up.

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:

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

QBoxLayout also includes two margin widths:

The margin defaults to 0. The spacing defaults to the same as the margin width for a top-level layout, or to the same as the parent layout. Both are parameters to the constructor.

To remove a widget from a layout, call remove(). 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 QGrid and Layout Overview.


Member Type Documentation

enum QBoxLayout::Direction

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

QBoxLayout::LeftToRightQt::Horizontal, from left to right
QBoxLayout::RightToLeftQt::Horizontal, from right to left
QBoxLayout::TopToBottomQt::Vertical, from top to bottom
QBoxLayout::DownThe same as TopToBottom
QBoxLayout::BottomToTopQt::Vertical, from bottom to top
QBoxLayout::UpThe same as BottomToTop

Member Function Documentation

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

Constructs a new QBoxLayout with direction dir and parent widget parent. parent may not be 0.

See also direction().

QBoxLayout::QBoxLayout ( Direction dir )

Constructs a new QBoxLayout with direction dir.

You must insert this box into another layout.

QBoxLayout::~QBoxLayout ()

Destroys this box layout.

The layout's widgets aren't destroyed.

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

Adds item to the end of this box layout.

Reimplemented from QLayout.

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

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

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

void QBoxLayout::addSpacing ( int size )

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

See also insertSpacing() and addStretch().

void QBoxLayout::addStretch ( int stretch = 0 )

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

See also addSpacing().

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.

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

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.

From Qt 3.0, the alignment parameter is interpreted more aggressively than in previous versions of Qt. A non-default alignment now indicates that the widget should not grow to fill the available space, but should be sized according to sizeHint().

See also insertWidget(), addLayout(), and addSpacing().

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 QBoxLayout::Direction, addWidget(), and addSpacing().

QSizePolicy::ExpandData QBoxLayout::expanding () const   [virtual]

Returns whether this layout 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 BothDirections means that it wants to grow in both dimensions.

Reimplemented from QLayoutItem.

int QBoxLayout::findWidget ( QWidget * w )

Searches for widget w in this layout (not including child layouts).

Returns the index of w, or -1 if w is not found.

bool QBoxLayout::hasHeightForWidth () const   [virtual]

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

Reimplemented from QLayoutItem.

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

Returns the layout's preferred height when it is w pixels wide.

Reimplemented from QLayoutItem.

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

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

Warning: Does not call QLayout::insertChildLayout() if item is a QLayout.

See also addItem() and findWidget().

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 insertWidget() and insertSpacing().

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

Inserts a non-stretchable space 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 insertStretch().

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

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

See also insertSpacing().

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

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.

From Qt 3.0, the alignment parameter is interpreted more aggressively than in previous versions of Qt. A non-default alignment now indicates that the widget should not grow to fill the available space, but should be sized according to sizeHint().

See also insertLayout() and insertSpacing().

void QBoxLayout::invalidate ()   [virtual]

Resets cached information.

Reimplemented from QLayoutItem.

QSize QBoxLayout::maximumSize () const   [virtual]

Returns the maximum size needed by this box layout.

Reimplemented from QLayoutItem.

QSize QBoxLayout::minimumSize () const   [virtual]

Returns the minimum size needed by this box layout.

Reimplemented from QLayoutItem.

bool QBoxLayout::setAlignment ( QWidget * w, Qt::Alignment alignment )

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

See also setStretchFactor().

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Sets the alignment for the box layout to be alignment.

bool QBoxLayout::setAlignment ( QLayout * l, Qt::Alignment alignment )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

void QBoxLayout::setDirection ( Direction direction )

Sets the direction of this layout to direction.

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

Resizes managed widgets within the rectangle r.

Reimplemented from QLayoutItem.

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

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

See also setAlignment().

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

QSize QBoxLayout::sizeHint () const   [virtual]

Returns the preferred size of this box layout.

Reimplemented from QLayoutItem.


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Qt 4.0.0-b1