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/****************************************************************************
**
** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
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** rights. These rights are described in the Nokia Qt LGPL Exception
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****************************************************************************/
/*!
\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.
*/
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