source: trunk/doc/src/tutorials/widgets-tutorial.qdoc@ 109

/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
** Contact: Qt Software Information ([email protected])
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** 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 [email protected].
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \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