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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** All rights reserved.
** Contact: Nokia Corporation (qt-info@nokia.com)
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** This file is part of the documentation of the Qt Toolkit.
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** contained in the Technology Preview License Agreement accompanying
** this package.
**
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** Foundation and appearing in the file LICENSE.LGPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU Lesser General Public License version 2.1 requirements
** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
**
** In addition, as a special exception, Nokia gives you certain additional
** rights. These rights are described in the Nokia Qt LGPL Exception
** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
**
** If you have questions regarding the use of this file, please contact
** Nokia at qt-info@nokia.com.
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** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\example graphicsview/basicgraphicslayouts
\title Basic Graphics Layouts Example
The Basic Graphics Layouts example shows how to use the layout classes
in QGraphicsView: QGraphicsLinearLayout and QGraphicsGridLayout.
In addition to that it shows how to write your own custom layout item.
\image basicgraphicslayouts-example.png Screenshot of the Basic Layouts Example
\section1 Window Class Definition
The \c Window class is a subclass of QGraphicsWidget. It has a
constructor with a QGraphicsWidget \a parent as its parameter.
\snippet examples/graphicsview/basicgraphicslayouts/window.h 0
\section1 Window Class Implementation
The constructor of \c Window instantiates a QGraphicsLinearLayout object,
\c windowLayout, with vertical orientation. We instantiate another
QGraphicsLinearLayout object, \c linear, whose parent is \c windowLayout.
Next, we create a \c LayoutItem object, \c item and add it to \c linear
with the \l{QGraphicsLinearLayout::}{addItem()} function. We also provide
\c item with a \l{QGraphicsLinearLayout::setStretchFactor()}
{stretchFactor}.
\snippet examples/graphicsview/basicgraphicslayouts/window.cpp 0
We repeat the process:
\list
\o create a new \c LayoutItem,
\o add the item \c linear, and
\o provide a stretch factor.
\endlist
\snippet examples/graphicsview/basicgraphicslayouts/window.cpp 1
We then add \c linear to \c windowLayout, nesting two
QGraphicsLinearLayout objects. Apart from the QGraphicsLinearLayout, we
also use a QGraphicsGridLayout object, \c grid, which is a 4x3 grid with
some cells spanning to other rows.
We create seven \c LayoutItem objects and place them into \c grid with
the \l{QGraphicsGridLayout::}{addItem()} function as shown in the code
snippet below:
\snippet examples/graphicsview/basicgraphicslayouts/window.cpp 2
The first item we add to \c grid is placed in the top left cell,
spanning four rows. The next two items are placed in the second column,
and they span two rows. Each item's \l{QGraphicsWidget::}{maximumHeight()}
and \l{QGraphicsWidget::}{minimumHeight()} are set to be equal so that
they do not expand vertically. As a result, these items will not
fit vertically in their cells. So, we specify that they should be
vertically aligned in the center of the cell using Qt::AlignVCenter.
Finally, \c grid itself is added to \c windowLayout. Unlike
QGridLayout::addItem(), QGraphicsGridLayout::addItem() requires a row
and a column for its argument, specifying which cell the item should be
positioned in. Also, if the \c rowSpan and \c columnSpan arguments
are omitted, they will default to 1.
Note that we do not specify a parent for each \c LayoutItem that we
construct, as all these items will be added to \c windowLayout. When we
add an item to a layout, it will be automatically reparented to the widget
on which the layout is installed.
\snippet examples/graphicsview/basicgraphicslayouts/window.cpp 3
Now that we have set up \c grid and added it to \c windowLayout, we
install \c windowLayout onto the window object using
QGraphicsWidget::setLayout() and we set the window title.
\section1 LayoutItem Class Definition
The \c LayoutItem class is a subclass of QGraphicsLayoutItem and
QGraphicsItem. It has a constructor, a destructor, and some required
reimplementations.
Since it inherits QGraphicsLayoutItem it must reimplement
{QGraphicsLayoutItem::setGeometry()}{setGeometry()} and
{QGraphicsLayoutItem::sizeHint()}{sizeHint()}.
In addition to that it inherits QGraphicsItem, so it must reimplement
{QGraphicsItem::boundingRect()}{boundingRect()} and
{QGraphicsItem::paint()}{paint()}.
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.h 0
The \c LayoutItem class also has a private instance of QPixmap, \c m_pix.
\section1 LayoutItem Class Implementation
In \c{LayoutItem}'s constructor, \c m_pix is instantiated and the
\c{block.png} image is loaded into it.
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 0
We use the Q_UNUSED() macro to prevent the compiler from generating
warnings regarding unused parameters.
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 1
The idea behind the \c paint() function is to paint the
background rect then paint a rect around the pixmap.
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 2
The reimplementation of {QGraphicsItem::boundingRect()}{boundingRect()}
will set the top left corner at (0,0), and the size of it will be
the size of the layout items
{QGraphicsLayoutItem::geometry()}{geometry()}. This is the area that
we paint within.
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 3
The reimplementation of {QGraphicsLayoutItem::setGeometry()}{setGeometry()}
simply calls its baseclass implementation. However, since this will change
the boundingRect we must also call
{QGraphicsItem::prepareGeometryChange()}{prepareGeometryChange()}.
Finally, we move the item according to \c geom.topLeft().
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 4
Since we don't want the size of the item to be smaller than the pixmap, we
must make sure that we return a size hint that is larger than \c m_pix.
We also add some extra space around for borders that we will paint later.
Alternatively, you could scale the pixmap to prevent the item from
becoming smaller than the pixmap.
The preferred size is the same as the minimum size hint, while we set
maximum to be a large value
\snippet examples/graphicsview/basicgraphicslayouts/layoutitem.cpp 5
*/
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