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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information (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.
** You may use this file in accordance with the terms and conditions
** contained in the either Technology Preview License Agreement or the
** Beta Release License Agreement.
**
** 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 1.0, included in the file LGPL_EXCEPTION.txt in this
** package.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3.0 as published by the Free Software
** Foundation and appearing in the file LICENSE.GPL included in the
** packaging of this file. Please review the following information to
** ensure the GNU General Public License version 3.0 requirements will be
** met: http://www.gnu.org/copyleft/gpl.html.
**
** If you are unsure which license is appropriate for your use, please
** contact the sales department at qt-sales@nokia.com.
** $QT_END_LICENSE$
**
****************************************************************************/
/*!
\page widgets-tutorial.html
\title Widgets Tutorial
\ingroup tutorials
\brief This tutorial covers basic usage of widgets and layouts, showing how they are used to build GUI applications.
\section1 Introduction
Widgets are the basic building blocks of graphical user interface (GUI)
applications made with Qt. Each GUI component, such as a button, label or
text editor, is a widget and can be placed within an existing user
interface or displayed as an independent window. Each type of component
is provided by a particular subclass of QWidget, which is itself a
subclass of QObject.
QWidget is not an abstract class; it can be used as a container for other
widgets, and can be subclassed with minimal effort to create custom
widgets. It is most often used to create windows in which other widgets
are placed.
As with \l{QObject}s, widgets can be created with parent objects to
indicate ownership, ensuring that objects are deleted when they are no
longer used. With widgets, these parent-child relationships have an
additional meaning: each child is displayed within the screen area
occupied by its parent. This means that, when a window is deleted, all
the widgets it contains are automatically deleted.
\section1 Creating a Window
If a widget is created without a parent, it is treated as a window, or
\e{top-level widget}, when it is shown. Since it has no parent object to
ensure that it is deleted when no longer needed, it is up to the
developer to keep track of the top-level widgets in an application.
In the following example, we use QWidget to create and show a window with
a default size:
\raw HTML
<table align="left" width="100%">
<tr class="qt-code"><td>
\endraw
\snippet snippets/widgets-tutorial/toplevel/main.cpp create, resize and show
\raw HTML
</td><td align="right">
\endraw
\inlineimage widgets-tutorial-toplevel.png
\raw HTML
</td></tr>
</table>
\endraw
We can add a child widget to this window by passing \c window as the
parent to its constructor. In this case, we add a button to the window
and place it in a specific location:
\raw HTML
<table align="left" width="100%">
<tr class="qt-code"><td>
\endraw
\snippet snippets/widgets-tutorial/childwidget/main.cpp create, position and show
\raw HTML
</td><td align="right">
\endraw
\inlineimage widgets-tutorial-childwidget.png
\raw HTML
</td></tr>
</table>
\endraw
The button is now a child of the window and will be deleted when the
window is destroyed. Note that hiding or closing the window does not
automatically destroy it.
\section1 Using Layouts
Usually, child widgets are arranged inside a window using layout objects
rather than by specifying positions and sizes explicitly. Here, we
construct a label and line edit widget that we would like to arrange
side-by-side.
\raw HTML
<table align="left" width="100%">
<tr class="qt-code"><td>
\endraw
\snippet snippets/widgets-tutorial/windowlayout/main.cpp create, lay out widgets and show
\raw HTML
</td><td align="right">
\endraw
\inlineimage widgets-tutorial-windowlayout.png
\raw HTML
</td></tr>
</table>
\endraw
The \c layout object we construct manages the positions and sizes of
widgets supplied to it with the \l{QHBoxLayout::}{addWidget()} function.
The layout itself is supplied to the window itself in the call to
\l{QWidget::}{setLayout()}. Layouts are only visible through the effects
they have on the widgets (and other layouts) they are responsible for
managing.
In the example above, the ownership of each widget is not immediately
clear. Since we construct the widgets and the layout without parent
objects, we would expect to see an empty window and two separate windows
containing a label and a line edit. However, when we tell the layout to
manage the label and line edit and set the layout on the window, both the
widgets and the layout itself are ''reparented'' to become children of
the window.
Just as widgets can contain other widgets, layouts can be used to provide
different levels of grouping for widgets. Here, we want to display a
label alongside a line edit at the top of a window, above a table view
showing the results of a query.
\raw HTML
<table align="left" width="100%">
<tr class="qt-code"><td>
\endraw
\snippet snippets/widgets-tutorial/nestedlayouts/main.cpp create, lay out widgets and show
\raw HTML
</td><td align="right">
\endraw
\inlineimage widgets-tutorial-nestedlayouts.png
\raw HTML
</td></tr>
</table>
\endraw
As well as QHBoxLayout and QVBoxLayout, Qt also provides QGridLayout
and QFormLayout classes to help with more complex user interfaces.
*/
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