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43 \example desktop/systray
44 \title System Tray Icon Example
47 The System Tray Icon example shows how to add an icon with a menu
48 and popup messages to a desktop environment's system tray.
50 \image systemtray-example.png Screenshot of the System Tray Icon.
52 Modern operating systems usually provide a special area on the
53 desktop, called the system tray or notification area, where
54 long-running applications can display icons and short messages.
56 This example consists of one single class, \c Window, providing
57 the main application window (i.e., an editor for the system tray
58 icon) and the associated icon.
60 \image systemtray-editor.png
62 The editor allows the user to choose the preferred icon as well as
63 set the balloon message's type and duration. The user can also
64 edit the message's title and body. Finally, the editor provide a
65 checkbox controlling whether the icon is actually shown in the
68 \section1 Window Class Definition
70 The \c Window class inherits QWidget:
72 \snippet examples/desktop/systray/window.h 0
74 We implement several private slots to respond to user
75 interaction. The other private functions are only convenience
76 functions provided to simplify the constructor.
78 The tray icon is an instance of the QSystemTrayIcon class. To
79 check whether a system tray is present on the user's desktop, call
80 the static QSystemTrayIcon::isSystemTrayAvailable()
81 function. Associated with the icon, we provide a menu containing
82 the typical \gui minimize, \gui maximize, \gui restore and \gui
83 quit actions. We reimplement the QWidget::setVisible() function to
84 update the tray icon's menu whenever the editor's appearance
85 changes, e.g., when maximizing or minimizing the main application
88 Finally, we reimplement QWidget's \l {QWidget::}{closeEvent()}
89 function to be able to inform the user (when closing the editor
90 window) that the program will keep running in the system tray
91 until the user chooses the \gui Quit entry in the icon's context
94 \section1 Window Class Implementation
96 When constructing the editor widget, we first create the various
97 editor elements before we create the actual system tray icon:
99 \snippet examples/desktop/systray/window.cpp 0
101 We ensure that the application responds to user input by
102 connecting most of the editor's input widgets (including the
103 system tray icon) to the application's private slots. But note the
104 visibility checkbox; its \l {QCheckBox::}{toggled()} signal is
105 connected to the \e {icon}'s \l {QSystemTrayIcon::}{setVisible()}
108 \snippet examples/desktop/systray/window.cpp 3
110 The \c setIcon() slot is triggered whenever the current index in
111 the icon combobox changes, i.e., whenever the user chooses another
112 icon in the editor. Note that it is also called when the user
113 activates the tray icon with the left mouse button, triggering the
114 icon's \l {QSystemTrayIcon::}{activated()} signal. We will come
115 back to this signal shortly.
117 The QSystemTrayIcon::setIcon() function sets the \l
118 {QSystemTrayIcon::}{icon} property that holds the actual system
119 tray icon. On Windows, the system tray icon size is 16x16; on X11,
120 the preferred size is 22x22. The icon will be scaled to the
121 appropriate size as necessary.
123 Note that on X11, due to a limitation in the system tray
124 specification, mouse clicks on transparent areas in the icon are
125 propagated to the system tray. If this behavior is unacceptable,
126 we suggest using an icon with no transparency.
128 \snippet examples/desktop/systray/window.cpp 4
130 Whenever the user activates the system tray icon, it emits its \l
131 {QSystemTrayIcon::}{activated()} signal passing the triggering
132 reason as parameter. QSystemTrayIcon provides the \l
133 {QSystemTrayIcon::}{ActivationReason} enum to describe how the
136 In the constructor, we connected our icon's \l
137 {QSystemTrayIcon::}{activated()} signal to our custom \c
138 iconActivated() slot: If the user has clicked the icon using the
139 left mouse button, this function changes the icon image by
140 incrementing the icon combobox's current index, triggering the \c
141 setIcon() slot as mentioned above. If the user activates the icon
142 using the middle mouse button, it calls the custom \c
145 \snippet examples/desktop/systray/window.cpp 5
147 When the \e showMessage() slot is triggered, we first retrieve the
148 message icon depending on the currently chosen message type. The
149 QSystemTrayIcon::MessageIcon enum describes the icon that is shown
150 when a balloon message is displayed. Then we call
151 QSystemTrayIcon's \l {QSystemTrayIcon::}{showMessage()} function
152 to show the message with the title, body, and icon for the time
153 specified in milliseconds.
155 Mac OS X users note: The Growl notification system must be
156 installed for QSystemTrayIcon::showMessage() to display messages.
158 QSystemTrayIcon also has the corresponding, \l {QSystemTrayIcon::}
159 {messageClicked()} signal, which is emitted when the user clicks a
160 message displayed by \l {QSystemTrayIcon::}{showMessage()}.
162 \snippet examples/desktop/systray/window.cpp 6
164 In the constructor, we connected the \l
165 {QSystemTrayIcon::}{messageClicked()} signal to our custom \c
166 messageClicked() slot that simply displays a message using the
169 QMessageBox provides a modal dialog with a short message, an icon,
170 and buttons laid out depending on the current style. It supports
171 four severity levels: "Question", "Information", "Warning" and
172 "Critical". The easiest way to pop up a message box in Qt is to
173 call one of the associated static functions, e.g.,
174 QMessageBox::information().
176 As we mentioned earlier, we reimplement a couple of QWidget's
179 \snippet examples/desktop/systray/window.cpp 1
181 Our reimplementation of the QWidget::setVisible() function updates
182 the tray icon's menu whenever the editor's appearance changes,
183 e.g., when maximizing or minimizing the main application window,
184 before calling the base class implementation.
186 \snippet examples/desktop/systray/window.cpp 2
188 We have reimplemented the QWidget::closeEvent() event handler to
189 receive widget close events, showing the above message to the
190 users when they are closing the editor window.
192 In addition to the functions and slots discussed above, we have
193 also implemented several convenience functions to simplify the
194 constructor: \c createIconGroupBox(), \c createMessageGroupBox(),
195 \c createActions() and \c createTrayIcon(). See the \l
196 {desktop/systray/window.cpp}{window.cpp} file for details.