/****************************************************************************

**

** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).

** All rights reserved.

** 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.

** You may use this file in accordance with the terms and conditions

** 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.

**

**

**

**

**

**

**

**

** $QT_END_LICENSE$

**

****************************************************************************/

/*!

    \example desktop/systray

    \title System Tray Icon Example

    The System Tray Icon example shows how to add an icon with a menu

    and popup messages to a desktop environment's system tray.

    \image systemtray-example.png Screenshot of the System Tray Icon.

    Modern operating systems usually provide a special area on the

    desktop, called the system tray or notification area, where

    long-running applications can display icons and short messages.

    This example consists of one single class, \c Window, providing

    the main application window (i.e., an editor for the system tray

    icon) and the associated icon.

    \image systemtray-editor.png

    The editor allows the user to choose the preferred icon as well as

    set the balloon message's type and duration. The user can also

    edit the message's title and body. Finally, the editor provide a

    checkbox controlling whether the icon is actually shown in the

    system tray, or not.

    \section1 Window Class Definition

    The \c Window class inherits QWidget:

    \snippet examples/desktop/systray/window.h 0

    We implement several private slots to respond to user

    interaction. The other private functions are only convenience

    functions provided to simplify the constructor.

    The tray icon is an instance of the QSystemTrayIcon class. To

    check whether a system tray is present on the user's desktop, call

    the static QSystemTrayIcon::isSystemTrayAvailable()

    function. Associated with the icon, we provide a menu containing

    the typical \gui minimize, \gui maximize, \gui restore and \gui

    quit actions. We reimplement the QWidget::setVisible() function to

    update the tray icon's menu whenever the editor's appearance

    changes, e.g., when maximizing or minimizing the main application

    window.

    Finally, we reimplement QWidget's \l {QWidget::}{closeEvent()}

    function to be able to inform the user (when closing the editor

    window) that the program will keep running in the system tray

    until the user chooses the \gui Quit entry in the icon's context

    menu.

    \section1 Window Class Implementation

    When constructing the editor widget, we first create the various

    editor elements before we create the actual system tray icon:

    \snippet examples/desktop/systray/window.cpp 0

    We ensure that the application responds to user input by

    connecting most of the editor's input widgets (including the

    system tray icon) to the application's private slots. But note the

    visibility checkbox; its \l {QCheckBox::}{toggled()} signal is

    connected to the \e {icon}'s \l {QSystemTrayIcon::}{setVisible()}

    function instead.

    \snippet examples/desktop/systray/window.cpp 3

    The \c setIcon() slot is triggered whenever the current index in

    the icon combobox changes, i.e., whenever the user chooses another

    icon in the editor. Note that it is also called when the user

    activates the tray icon with the left mouse button, triggering the

    icon's \l {QSystemTrayIcon::}{activated()} signal. We will come

    back to this signal shortly.

    The QSystemTrayIcon::setIcon() function sets the \l

    {QSystemTrayIcon::}{icon} property that holds the actual system

    tray icon. On Windows, the system tray icon size is 16x16; on X11,

    the preferred size is 22x22. The icon will be scaled to the

    appropriate size as necessary.

    Note that on X11, due to a limitation in the system tray

    specification, mouse clicks on transparent areas in the icon are

    propagated to the system tray. If this behavior is unacceptable,

    we suggest using an icon with no transparency.

    \snippet examples/desktop/systray/window.cpp 4

    Whenever the user activates the system tray icon, it emits its \l

    {QSystemTrayIcon::}{activated()} signal passing the triggering

    reason as parameter. QSystemTrayIcon provides the \l

    {QSystemTrayIcon::}{ActivationReason} enum to describe how the

    icon was activated.

    In the constructor, we connected our icon's \l

    {QSystemTrayIcon::}{activated()} signal to our custom \c

    iconActivated() slot: If the user has clicked the icon using the

    left mouse button, this function changes the icon image by

    incrementing the icon combobox's current index, triggering the \c

    setIcon() slot as mentioned above. If the user activates the icon

    using the middle mouse button, it calls the custom \c

    showMessage() slot:

    \snippet examples/desktop/systray/window.cpp 5

    When the \e showMessage() slot is triggered, we first retrieve the

    message icon depending on the currently chosen message type. The

    QSystemTrayIcon::MessageIcon enum describes the icon that is shown

    when a balloon message is displayed. Then we call

    QSystemTrayIcon's \l {QSystemTrayIcon::}{showMessage()} function

    to show the message with the title, body, and icon for the time

    specified in milliseconds.

    Mac OS X users note: The Growl notification system must be

    installed for QSystemTrayIcon::showMessage() to display messages.

    QSystemTrayIcon also has the corresponding, \l {QSystemTrayIcon::}

    {messageClicked()} signal, which is emitted when the user clicks a

    message displayed by \l {QSystemTrayIcon::}{showMessage()}.

    \snippet examples/desktop/systray/window.cpp 6

    In the constructor, we connected the \l

    {QSystemTrayIcon::}{messageClicked()} signal to our custom \c

    messageClicked() slot that simply displays a message using the

    QMessageBox class.

    QMessageBox provides a modal dialog with a short message, an icon,

    and buttons laid out depending on the current style. It supports

    four severity levels: "Question", "Information", "Warning" and

    "Critical". The easiest way to pop up a message box in Qt is to

    call one of the associated static functions, e.g.,

    QMessageBox::information().

    As we mentioned earlier, we reimplement a couple of QWidget's

    virtual functions:

    \snippet examples/desktop/systray/window.cpp 1

    Our reimplementation of the QWidget::setVisible() function updates

    the tray icon's menu whenever the editor's appearance changes,

    e.g., when maximizing or minimizing the main application window,

    before calling the base class implementation.

    \snippet examples/desktop/systray/window.cpp 2

    We have reimplemented the QWidget::closeEvent() event handler to

    receive widget close events, showing the above message to the

    users when they are closing the editor window.

    In addition to the functions and slots discussed above, we have

    also implemented several convenience functions to simplify the

    constructor: \c createIconGroupBox(), \c createMessageGroupBox(),

    \c createActions() and \c createTrayIcon(). See the \l

    {desktop/systray/window.cpp}{window.cpp} file for details.

*/