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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Nokia Corporation (qt-info@nokia.com)
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** No Commercial Usage
** This file contains pre-release code and may not be distributed.
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** contained in the Technology Preview License Agreement accompanying
** this package.
**
** GNU Lesser General Public License Usage
** Alternatively, this file may be used under the terms of the GNU Lesser
** General Public License version 2.1 as published by the Free Software
** 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 layouts/flowlayout
\title Flow Layout Example
The Flow Layout example demonstrates a custom layout that arranges child
widgets from left to right and top to bottom in a top-level widget.
\image flowlayout-example.png Screenshot of the Flow Layout example
The items are first laid out horizontally and then vertically when each line
in the layout runs out of space.
The Flowlayout class mainly uses QLayout and QWidgetItem, while the
Window uses QWidget and QLabel. We will only document the definition
and implementation of \c FlowLayout below.
\section1 FlowLayout Class Definition
The \c FlowLayout class inherits QLayout. It is a custom layout class
that arranges its child widgets horizontally and vertically.
\snippet examples/layouts/flowlayout/flowlayout.h 0
We reimplement functions inherited from QLayout. These functions add items to
the layout and handle their orientation and geometry.
We also declare two private methods, \c doLayout() and \c smartSpacing().
\c doLayout() lays out the layout items, while the \c
smartSpacing() function calculates the spacing between them.
\section1 FlowLayout Class Implementation
We start off by looking at the constructor:
\snippet examples/layouts/flowlayout/flowlayout.cpp 1
In the constructor we call \c setContentsMargins() to set the left, top,
right and bottom margin. By default, QLayout uses values provided by
the current style (see QStyle::PixelMetric).
\snippet examples/layouts/flowlayout/flowlayout.cpp 2
In this example we reimplement \c addItem(), which is a pure virtual
function. When using \c addItem() the ownership of the layout items is
transferred to the layout, and it is therefore the layout's
responsibility to delete them.
\snippet examples/layouts/flowlayout/flowlayout.cpp 3
\c addItem() is implemented to add items to the layout.
\snippet examples/layouts/flowlayout/flowlayout.cpp 4
We implement \c horizontalSpacing() and \c verticalSpacing() to get
hold of the spacing between the widgets inside the layout. If the value
is less than or equal to 0, this value will be used. If not,
\c smartSpacing() will be called to calculate the spacing.
\snippet examples/layouts/flowlayout/flowlayout.cpp 5
We then implement \c count() to return the number of items in the
layout. To navigate the list of items we use \c itemAt() and
takeAt() to remove and return items from the list. If an item is
removed, the remaining items will be renumbered. All three
functions are pure virtual functions from QLayout.
\snippet examples/layouts/flowlayout/flowlayout.cpp 6
\c expandingDirections() returns the \l{Qt::Orientation}s in which the
layout can make use of more space than its \c sizeHint().
\snippet examples/layouts/flowlayout/flowlayout.cpp 7
To adjust to widgets of which height is dependent on width, we implement \c
heightForWidth(). The function \c hasHeightForWidth() is used to test for this
dependency, and \c heightForWidth() passes the width on to \c doLayout() which
in turn uses the width as an argument for the layout rect, i.e., the bounds in
which the items are laid out. This rect does not include the layout margin().
\snippet examples/layouts/flowlayout/flowlayout.cpp 8
\c setGeometry() is normally used to do the actual layout, i.e., calculate
the geometry of the layout's items. In this example, it calls \c doLayout()
and passes the layout rect.
\c sizeHint() returns the preferred size of the layout and \c minimumSize()
returns the minimum size of the layout.
\snippet examples/layouts/flowlayout/flowlayout.cpp 9
\c doLayout() handles the layout if \c horizontalSpacing() or \c
verticalSpacing() don't return the default value. It uses
\c getContentsMargins() to calculate the area available to the
layout items.
\snippet examples/layouts/flowlayout/flowlayout.cpp 10
It then sets the proper amount of spacing for each widget in the
layout, based on the current style.
\snippet examples/layouts/flowlayout/flowlayout.cpp 11
The position of each item in the layout is then calculated by
adding the items width and the line height to the initial x and y
coordinates. This in turn lets us find out whether the next item
will fit on the current line or if it must be moved down to the next.
We also find the height of the current line based on the widgets height.
\snippet examples/layouts/flowlayout/flowlayout.cpp 12
\c smartSpacing() is designed to get the default spacing for either
the top-level layouts or the sublayouts. The default spacing for
top-level layouts, when the parent is a QWidget, will be determined
by querying the style. The default spacing for sublayouts, when
the parent is a QLayout, will be determined by querying the spacing
of the parent layout.
*/
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