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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\example graphicsview/basicgraphicslayouts
\title Basic Graphics Layouts Example
\ingroup examples-graphicsview-layout
\brief Demonstrates how to create basic graphics layout.
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 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 graphicsview/basicgraphicslayouts/window.cpp 0
We repeat the process:
\list
\li create a new \c LayoutItem,
\li add the item \c linear, and
\li provide a stretch factor.
\endlist
\snippet 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 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 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 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 graphicsview/basicgraphicslayouts/layoutitem.cpp 0
We use the Q_UNUSED() macro to prevent the compiler from generating
warnings regarding unused parameters.
\snippet 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 graphicsview/basicgraphicslayouts/layoutitem.cpp 2
The reimplementation of \l{QGraphicsItem::}{boundingRect()}
will set the top left corner at (0,0), and the size of it will be
the size of the layout items
\l{QGraphicsLayoutItem::}{geometry()}. This is the area that
we paint within.
\snippet graphicsview/basicgraphicslayouts/layoutitem.cpp 3
The reimplementation of \l{QGraphicsLayoutItem::setGeometry()}{setGeometry()}
simply calls its baseclass implementation. However, since this will change
the boundingRect we must also call
\l{QGraphicsItem::prepareGeometryChange()}{prepareGeometryChange()}.
Finally, we move the item according to \c geom.topLeft().
\snippet 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 graphicsview/basicgraphicslayouts/layoutitem.cpp 5
*/
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