- Qt 6.6
- Qt GUI
- C++ Classes
- QGuiApplication
- Qt 6.6.0 Reference Documentation

# QGuiApplication Class

The QGuiApplication class manages the GUI application's control flow and main settings. More...

Header: | #include <QGuiApplication>
CMake: | find_package(Qt6 REQUIRED COMPONENTS Gui) target_link_libraries(mytarget PRIVATE Qt6::Gui)
qmake: | QT += gui
Inherits: | QCoreApplication
Inherited By: | QApplication

- List of all members, including inherited members
- Deprecated members

## Properties

applicationDisplayName : QString desktopFileName : QString layoutDirection : Qt::LayoutDirection platformName : const QString | primaryScreen : QScreen* const quitOnLastWindowClosed : bool windowIcon : QIcon

## Public Functions

| QGuiApplication(int &argc, char **argv)
virtual | ~QGuiApplication()
qreal | devicePixelRatio() const
bool | isSavingSession() const
bool | isSessionRestored() const
QNativeInterface * | nativeInterface() const
QString | sessionId() const
QString | sessionKey() const

## Reimplemented Public Functions

virtual bool | notify(QObject *object, QEvent *event) override

## Public Slots

void | setBadgeNumber(qint64 number)

## Signals

void | applicationDisplayNameChanged()
void | applicationStateChanged(Qt::ApplicationState state)
void | commitDataRequest(QSessionManager &manager)
void | focusObjectChanged(QObject *focusObject)
void | focusWindowChanged(QWindow *focusWindow)
void | fontDatabaseChanged()
void | lastWindowClosed()
void | layoutDirectionChanged(Qt::LayoutDirection direction)
void | primaryScreenChanged(QScreen *screen)
void | saveStateRequest(QSessionManager &manager)
void | screenAdded(QScreen *screen)
void | screenRemoved(QScreen *screen)

## Static Public Members

QWindowList | allWindows()
QString | applicationDisplayName()
Qt::ApplicationState | applicationState()
void | changeOverrideCursor(const QCursor &cursor)
QClipboard * | clipboard()
QString | desktopFileName()
bool | desktopSettingsAware()
int | exec()
QObject * | focusObject()
QWindow * | focusWindow()
QFont | font()
Qt::HighDpiScaleFactorRoundingPolicy | highDpiScaleFactorRoundingPolicy()
QInputMethod * | inputMethod()
bool | isLeftToRight()
bool | isRightToLeft()
Qt::KeyboardModifiers | keyboardModifiers()
Qt::LayoutDirection | layoutDirection()
QWindow * | modalWindow()
Qt::MouseButtons | mouseButtons()
QCursor * | overrideCursor()
QPalette | palette()
QString | platformName()
QScreen * | primaryScreen()
Qt::KeyboardModifiers | queryKeyboardModifiers()
bool | quitOnLastWindowClosed()
void | restoreOverrideCursor()
QScreen * | screenAt(const QPoint &point)
QList<QScreen *> | screens()
void | setApplicationDisplayName(const QString &name)
void | setDesktopFileName(const QString &name)
void | setDesktopSettingsAware(bool on)
void | setFont(const QFont &font)
void | setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy policy)
void | setLayoutDirection(Qt::LayoutDirection direction)
void | setOverrideCursor(const QCursor &cursor)
void | setPalette(const QPalette &pal)
void | setQuitOnLastWindowClosed(bool quit)
void | setWindowIcon(const QIcon &icon)
QStyleHints * | styleHints()
void | sync()
QWindow * | topLevelAt(const QPoint &pos)
QWindowList | topLevelWindows()
QIcon | windowIcon()

## Reimplemented Protected Functions

virtual bool | event(QEvent *e) override

## Macros

| qGuiApp

## Detailed Description

QGuiApplication contains the main event loop, where all events from the window system and other sources are processed and dispatched. It also handles the application's initialization and finalization, and provides session management. In addition, QGuiApplication handles most of the system-wide and application-wide settings.

For any GUI application using Qt, there is precisely one QGuiApplication object no matter whether the application has 0, 1, 2 or more windows at any given time. For non-GUI Qt applications, use QCoreApplication instead, as it does not depend on the Qt GUI module. For QWidget based Qt applications, use QApplication instead, as it provides some functionality needed for creating QWidget instances.

The QGuiApplication object is accessible through the instance() function, which returns a pointer equivalent to the global qApp pointer.

QGuiApplication's main areas of responsibility are:

- It initializes the application with the user's desktop settings, such as palette(), font() and styleHints(). It keeps track of these properties in case the user changes the desktop globally, for example, through some kind of control panel.
- It performs event handling, meaning that it receives events from the underlying window system and dispatches them to the relevant widgets. You can send your own events to windows by using sendEvent() and postEvent().
- It parses common command line arguments and sets its internal state accordingly. See the constructor documentation below for more details.
- It provides localization of strings that are visible to the user via translate().
- It provides some magical objects like the clipboard().
- It knows about the application's windows. You can ask which window is at a certain position using topLevelAt(), get a list of topLevelWindows(), etc.
- It manages the application's mouse cursor handling, see setOverrideCursor()
- It provides support for sophisticated session management. This makes it possible for applications to terminate gracefully when the user logs out, to cancel a shutdown process if termination isn't possible and even to preserve the entire application's state for a future session. See isSessionRestored(), sessionId() and commitDataRequest() and saveStateRequest() for details.

Since the QGuiApplication object does so much initialization, it must be created before any other objects related to the user interface are created. QGuiApplication also deals with common command line arguments. Hence, it is usually a good idea to create it before any interpretation or modification of `argv` is done in the application itself.

Groups of functions
System settings | desktopSettingsAware(), setDesktopSettingsAware(), styleHints(), palette(), setPalette(), font(), setFont().
Event handling | exec(), processEvents(), exit(), quit(). sendEvent(), postEvent(), sendPostedEvents(), removePostedEvents(), notify().
Windows | allWindows(), topLevelWindows(), focusWindow(), clipboard(), topLevelAt().
Advanced cursor handling | overrideCursor(), setOverrideCursor(), restoreOverrideCursor().
Session management | isSessionRestored(), sessionId(), commitDataRequest(), saveStateRequest().
Miscellaneous | startingUp(), closingDown().

See also QCoreApplication, QAbstractEventDispatcher, and QEventLoop.

## Property Documentation

### applicationDisplayName : QString

This property holds the user-visible name of this application

This name is shown to the user, for instance in window titles. It can be translated, if necessary.

If not set, the application display name defaults to the application name.

Access functions:

QString | applicationDisplayName()
void | setApplicationDisplayName(const QString &name)

Notifier signal:

void | applicationDisplayNameChanged()

See also applicationName.

### desktopFileName : QString

This property holds the base name of the desktop entry for this application

This is the file name, without the full path or the trailing ".desktop" extension of the desktop entry that represents this application according to the freedesktop desktop entry specification.

This property gives a precise indication of what desktop entry represents the application and it is needed by the windowing system to retrieve such information without resorting to imprecise heuristics.

The latest version of the freedesktop desktop entry specification can be obtained here.

Access functions:

QString | desktopFileName()
void | setDesktopFileName(const QString &name)

### layoutDirection : Qt::LayoutDirection

This property holds the default layout direction for this application

On system start-up, or when the direction is explicitly set to Qt::LayoutDirectionAuto, the default layout direction depends on the application's language.

The notifier signal was introduced in Qt 5.4.

Access functions:

Qt::LayoutDirection | layoutDirection()
void | setLayoutDirection(Qt::LayoutDirection direction)

Notifier signal:

void | layoutDirectionChanged(Qt::LayoutDirection direction)

See also QWidget::layoutDirection, isLeftToRight(), and isRightToLeft().

### `[read-only]` platformName : const QString

This property holds the name of the underlying platform plugin.

The QPA platform plugins are located in `qtbase\src\plugins\platforms`. At the time of writing, the following platform plugin names are supported:

- `android`
- `cocoa` is a platform plugin for macOS.
- `directfb`
- `eglfs` is a platform plugin for running Qt5 applications on top of EGL and OpenGL ES 2.0 without an actual windowing system (like X11 or Wayland). For more information, see EGLFS.
- `ios` (also used for tvOS)
- `linuxfb` writes directly to the framebuffer. For more information, see LinuxFB.
- `minimal` is provided as an examples for developers who want to write their own platform plugins. However, you can use the plugin to run GUI applications in environments without a GUI, such as servers.
- `minimalegl` is an example plugin.
- `offscreen`
- `qnx`
- `windows`
- `wayland` is a platform plugin for the Wayland display server protocol, used on some Linux desktops and embedded systems.
- `xcb` is a plugin for the X11 window system, used on some desktop Linux platforms.

Note: Calling this function without a QGuiApplication will return the default platform name, if available. The default platform name is not affected by the `-platform` command line option, or the `QT_QPA_PLATFORM` environment variable.

For more information about the platform plugins for embedded Linux devices, see Qt for Embedded Linux.

Access functions:

QString | platformName()

### `[read-only]` primaryScreen : QScreen* const

This property holds the primary (or default) screen of the application.

This will be the screen where QWindows are initially shown, unless otherwise specified.

The primaryScreenChanged signal was introduced in Qt 5.6.

Access functions:

QScreen * | primaryScreen()

Notifier signal:

void | primaryScreenChanged(QScreen *screen)

See also screens().

### quitOnLastWindowClosed : bool

This property holds whether the application implicitly quits when the last window is closed.

The default is `true`.

If this property is `true`, the applications quits when the last visible primary window (i.e. top level window with no transient parent) is closed.

Access functions:

bool | quitOnLastWindowClosed()
void | setQuitOnLastWindowClosed(bool quit)

See also quit() and QWindow::close().

### windowIcon : QIcon

This property holds the default window icon

Access functions:

QIcon | windowIcon()
void | setWindowIcon(const QIcon &icon)

See also QWindow::setIcon() and Setting the Application Icon.

## Member Function Documentation

### QGuiApplication::QGuiApplication(int &argc, char **argv)

Initializes the window system and constructs an application object with argc command line arguments in argv.

Warning: The data referred to by argc and argv must stay valid for the entire lifetime of the QGuiApplication object. In addition, argc must be greater than zero and argv must contain at least one valid character string.

The global `qApp` pointer refers to this application object. Only one application object should be created.

This application object must be constructed before any paint devices (including pixmaps, bitmaps etc.).

Note: argc and argv might be changed as Qt removes command line arguments that it recognizes.

#### Supported Command Line Options

All Qt programs automatically support a set of command-line options that allow modifying the way Qt will interact with the windowing system. Some of the options are also accessible via environment variables, which are the preferred form if the application can launch GUI sub-processes or other applications (environment variables will be inherited by child processes). When in doubt, use the environment variables.

The options currently supported are the following:

- `-platform` platformName[:options], specifies the Qt Platform Abstraction (QPA) plugin.

  Overrides the `QT_QPA_PLATFORM` environment variable.

- `-platformpluginpath` path, specifies the path to platform plugins.

  Overrides the `QT_QPA_PLATFORM_PLUGIN_PATH` environment variable.

- `-platformtheme` platformTheme, specifies the platform theme.

  Overrides the `QT_QPA_PLATFORMTHEME` environment variable.

- `-plugin` plugin, specifies additional plugins to load. The argument may appear multiple times.

  Concatenated with the plugins in the `QT_QPA_GENERIC_PLUGINS` environment variable.

- `-qmljsdebugger=`, activates the QML/JS debugger with a specified port. The value must be of format `port:1234`[,block], where block is optional and will make the application wait until a debugger connects to it.
- `-qwindowgeometry` geometry, specifies window geometry for the main window using the X11-syntax. For example: `-qwindowgeometry 100x100+50+50`
- `-qwindowicon`, sets the default window icon
- `-qwindowtitle`, sets the title of the first window
- `-reverse`, sets the application's layout direction to Qt::RightToLeft. This option is intended to aid debugging and should not be used in production. The default value is automatically detected from the user's locale (see also QLocale::textDirection()).
- `-session` session, restores the application from an earlier session.

The following standard command line options are available for X11:

- `-display` hostname:screen_number, switches displays on X11.

  Overrides the `DISPLAY` environment variable.

- `-geometry` geometry, same as `-qwindowgeometry`.

#### Platform-Specific Arguments

You can specify platform-specific arguments for the `-platform` option. Place them after the platform plugin name following a colon as a comma-separated list. For example, `-platform windows:dialogs=xp,fontengine=freetype`.

The following parameters are available for `-platform windows`:

- `altgr`, detect the key `AltGr` found on some keyboards as Qt::GroupSwitchModifier (since Qt 5.12).
- `darkmode=[0|1|2]` controls how Qt responds to the activation of the Dark Mode for applications introduced in Windows 10 1903 (since Qt 5.15).

  A value of 0 disables dark mode support.

  A value of 1 causes Qt to switch the window borders to black when Dark Mode for applications is activated and no High Contrast Theme is in use. This is intended for applications that implement their own theming.

  A value of 2 will in addition cause the Windows Vista style to be deactivated and switch to the Windows style using a simplified palette in dark mode. This is currently experimental pending the introduction of new style that properly adapts to dark mode.

  As of Qt 6.5, the default value is 2; to disable dark mode support, set the value to 0 or 1.

- `dialogs=[xp|none]`, `xp` uses XP-style native dialogs and `none` disables them.
- `fontengine=freetype`, uses the FreeType font engine.
- `fontengine=directwrite`, uses the experimental DirectWrite font database and defaults to using the DirectWrite font engine (which is otherwise only used for some font types or font properties.) This affects font selection and aims to provide font naming more consistent with other platforms, but does not support all font formats, such as Postscript Type-1 or Microsoft FNT fonts.
- `menus=[native|none]`, controls the use of native menus.

  Native menus are implemented using Win32 API and are simpler than QMenu-based menus in for example that they do allow for placing widgets on them or changing properties like fonts and do not provide hover signals. They are mainly intended for Qt Quick. By default, they will be used if the application is not an instance of QApplication or for Qt Quick Controls 2 applications (since Qt 5.10).

- `nocolorfonts` Turn off DirectWrite Color fonts (since Qt 5.8).
- `nodirectwrite` Turn off DirectWrite fonts (since Qt 5.8).
- `nomousefromtouch` Ignores mouse events synthesized from touch events by the operating system.
- `nowmpointer` Switches from Pointer Input Messages handling to legacy mouse handling (since Qt 5.12).
- `reverse` Activates Right-to-left mode (experimental). Windows title bars will be shown accordingly in Right-to-left locales (since Qt 5.13).
- `tabletabsoluterange=<value>` Sets a value for mouse mode detection of WinTab tablets (Legacy, since Qt 5.3).

The following parameter is available for `-platform cocoa` (on macOS):

- `fontengine=freetype`, uses the FreeType font engine.

For more information about the platform-specific arguments available for embedded Linux platforms, see Qt for Embedded Linux.

See also arguments() and QGuiApplication::platformName.

### `[virtual noexcept]` QGuiApplication::~QGuiApplication()

Destructs the application.

### `[static]` QWindowList QGuiApplication::allWindows()

Returns a list of all the windows in the application.

The list is empty if there are no windows.

See also topLevelWindows().

### `[static]` Qt::ApplicationState QGuiApplication::applicationState()

Returns the current state of the application.

You can react to application state changes to perform actions such as stopping/resuming CPU-intensive tasks, freeing/loading resources or saving/restoring application data.

### `[signal]` void QGuiApplication::applicationStateChanged(Qt::ApplicationState state)

This signal is emitted when the state of the application changes.

See also applicationState().

### `[static]` void QGuiApplication::changeOverrideCursor(const QCursor &cursor)

Changes the currently active application override cursor to cursor.

This function has no effect if setOverrideCursor() was not called.

See also setOverrideCursor(), overrideCursor(), restoreOverrideCursor(), and QWidget::setCursor().

### `[static]` QClipboard *QGuiApplication::clipboard()

Returns the object for interacting with the clipboard.

### `[signal]` void QGuiApplication::commitDataRequest(QSessionManager &manager)

This signal deals with session management. It is emitted when the QSessionManager wants the application to commit all its data.

Usually this means saving all open files, after getting permission from the user. Furthermore you may want to provide a means by which the user can cancel the shutdown.

You should not exit the application within this signal. Instead, the session manager may or may not do this afterwards, depending on the context.

Warning: Within this signal, no user interaction is possible, unless you ask the manager for explicit permission. See QSessionManager::allowsInteraction() and QSessionManager::allowsErrorInteraction() for details and example usage.

Note: You should use Qt::DirectConnection when connecting to this signal.

See also isSessionRestored(), sessionId(), saveStateRequest(), and Session Management.

### `[static]` bool QGuiApplication::desktopSettingsAware()

Returns `true` if Qt is set to use the system's standard colors, fonts, etc.; otherwise returns `false`. The default is `true`.

See also setDesktopSettingsAware().

### qreal QGuiApplication::devicePixelRatio() const

Returns the highest screen device pixel ratio found on the system. This is the ratio between physical pixels and device-independent pixels.

Use this function only when you don't know which window you are targeting. If you do know the target window, use QWindow::devicePixelRatio() instead.

See also QWindow::devicePixelRatio().

### `[override virtual protected]` bool QGuiApplication::event(QEvent *e)

Reimplements: QCoreApplication::event(QEvent *e).

### `[static]` int QGuiApplication::exec()

Enters the main event loop and waits until exit() is called, and then returns the value that was set to exit() (which is 0 if exit() is called via quit()).

It is necessary to call this function to start event handling. The main event loop receives events from the window system and dispatches these to the application widgets.

Generally, no user interaction can take place before calling exec().

To make your application perform idle processing, e.g., executing a special function whenever there are no pending events, use a QTimer with 0 timeout. More advanced idle processing schemes can be achieved using processEvents().

We recommend that you connect clean-up code to the aboutToQuit() signal, instead of putting it in your application's `main()` function. This is because, on some platforms, the QApplication::exec() call may not return.

See also quitOnLastWindowClosed, quit(), exit(), processEvents(), and QCoreApplication::exec().

### `[static]` QObject *QGuiApplication::focusObject()

Returns the QObject in currently active window that will be final receiver of events tied to focus, such as key events.

### `[signal]` void QGuiApplication::focusObjectChanged(QObject *focusObject)

This signal is emitted when final receiver of events tied to focus is changed. focusObject is the new receiver.

See also focusObject().

### `[static]` QWindow *QGuiApplication::focusWindow()

Returns the QWindow that receives events tied to focus, such as key events.

See also QWindow::requestActivate().

### `[signal]` void QGuiApplication::focusWindowChanged(QWindow *focusWindow)

This signal is emitted when the focused window changes. focusWindow is the new focused window.

See also focusWindow().

### `[static]` QFont QGuiApplication::font()

Returns the default application font.

See also setFont().

### `[signal]` void QGuiApplication::fontDatabaseChanged()

This signal is emitted when the available fonts have changed.

This can happen when application fonts are added or removed, or when the system fonts change.

See also QFontDatabase::addApplicationFont(), QFontDatabase::addApplicationFontFromData(), QFontDatabase::removeAllApplicationFonts(), and QFontDatabase::removeApplicationFont().

### `[static]` Qt::HighDpiScaleFactorRoundingPolicy QGuiApplication::highDpiScaleFactorRoundingPolicy()

Returns the high-DPI scale factor rounding policy.

See also setHighDpiScaleFactorRoundingPolicy().

### `[static]` QInputMethod *QGuiApplication::inputMethod()

returns the input method.

The input method returns properties about the state and position of the virtual keyboard. It also provides information about the position of the current focused input element.

See also QInputMethod.

### `[static]` bool QGuiApplication::isLeftToRight()

Returns `true` if the application's layout direction is Qt::LeftToRight; otherwise returns `false`.

See also layoutDirection() and isRightToLeft().

### `[static]` bool QGuiApplication::isRightToLeft()

Returns `true` if the application's layout direction is Qt::RightToLeft; otherwise returns `false`.

See also layoutDirection() and isLeftToRight().

### bool QGuiApplication::isSavingSession() const

Returns `true` if the application is currently saving the session; otherwise returns `false`.

This is `true` when commitDataRequest() and saveStateRequest() are emitted, but also when the windows are closed afterwards by session management.

See also sessionId(), commitDataRequest(), and saveStateRequest().

### bool QGuiApplication::isSessionRestored() const

Returns `true` if the application has been restored from an earlier session; otherwise returns `false`.

See also sessionId(), commitDataRequest(), and saveStateRequest().

### `[static]` Qt::KeyboardModifiers QGuiApplication::keyboardModifiers()

Returns the current state of the modifier keys on the keyboard. The current state is updated synchronously as the event queue is emptied of events that will spontaneously change the keyboard state (QEvent::KeyPress and QEvent::KeyRelease events).

It should be noted this may not reflect the actual keys held on the input device at the time of calling but rather the modifiers as last reported in one of the above events. If no keys are being held Qt::NoModifier is returned.

See also mouseButtons() and queryKeyboardModifiers().

### `[signal]` void QGuiApplication::lastWindowClosed()

This signal is emitted from exec() when the last visible primary window (i.e. top level window with no transient parent) is closed.

By default, QGuiApplication quits after this signal is emitted. This feature can be turned off by setting quitOnLastWindowClosed to `false`.

See also QWindow::close(), QWindow::isTopLevel(), and QWindow::transientParent().

### `[static]` QWindow *QGuiApplication::modalWindow()

Returns the most recently shown modal window. If no modal windows are visible, this function returns zero.

A modal window is a window which has its modality property set to Qt::WindowModal or Qt::ApplicationModal. A modal window must be closed before the user can continue with other parts of the program.

Modal window are organized in a stack. This function returns the modal window at the top of the stack.

See also Qt::WindowModality and QWindow::setModality().

### `[static]` Qt::MouseButtons QGuiApplication::mouseButtons()

Returns the current state of the buttons on the mouse. The current state is updated synchronously as the event queue is emptied of events that will spontaneously change the mouse state (QEvent::MouseButtonPress and QEvent::MouseButtonRelease events).

It should be noted this may not reflect the actual buttons held on the input device at the time of calling but rather the mouse buttons as last reported in one of the above events. If no mouse buttons are being held Qt::NoButton is returned.

See also keyboardModifiers().

### template <typename QNativeInterface> QNativeInterface *QGuiApplication::nativeInterface() const

Returns a native interface of the given type for the application.

This function provides access to platform specific functionality of QGuiApplication, as defined in the QNativeInterface namespace:

QNativeInterface::QWaylandApplication | Native interface to a Wayland application
QNativeInterface::QX11Application | Native interface to an X11 application

If the requested interface is not available a `nullptr` is returned.

### `[override virtual]` bool QGuiApplication::notify(QObject *object, QEvent *event)

Reimplements: QCoreApplication::notify(QObject *receiver, QEvent *event).

### `[static]` QCursor *QGuiApplication::overrideCursor()

Returns the active application override cursor.

This function returns `nullptr` if no application cursor has been defined (i.e. the internal cursor stack is empty).

See also setOverrideCursor() and restoreOverrideCursor().

### `[static]` QPalette QGuiApplication::palette()

Returns the current application palette.

Roles that have not been explicitly set will reflect the system's platform theme.

See also setPalette().

### `[static]` Qt::KeyboardModifiers QGuiApplication::queryKeyboardModifiers()

Queries and returns the state of the modifier keys on the keyboard. Unlike keyboardModifiers, this method returns the actual keys held on the input device at the time of calling the method.

It does not rely on the keypress events having been received by this process, which makes it possible to check the modifiers while moving a window, for instance. Note that in most cases, you should use keyboardModifiers(), which is faster and more accurate since it contains the state of the modifiers as they were when the currently processed event was received.

See also keyboardModifiers().

### `[static]` void QGuiApplication::restoreOverrideCursor()

Undoes the last setOverrideCursor().

If setOverrideCursor() has been called twice, calling restoreOverrideCursor() will activate the first cursor set. Calling this function a second time restores the original widgets' cursors.

See also setOverrideCursor() and overrideCursor().

### `[signal]` void QGuiApplication::saveStateRequest(QSessionManager &manager)

This signal deals with session management. It is invoked when the session manager wants the application to preserve its state for a future session.

For example, a text editor would create a temporary file that includes the current contents of its edit buffers, the location of the cursor and other aspects of the current editing session.

You should never exit the application within this signal. Instead, the session manager may or may not do this afterwards, depending on the context. Furthermore, most session managers will very likely request a saved state immediately after the application has been started. This permits the session manager to learn about the application's restart policy.

Warning: Within this signal, no user interaction is possible, unless you ask the manager for explicit permission. See QSessionManager::allowsInteraction() and QSessionManager::allowsErrorInteraction() for details.

Note: You should use Qt::DirectConnection when connecting to this signal.

See also isSessionRestored(), sessionId(), commitDataRequest(), and Session Management.

### `[signal]` void QGuiApplication::screenAdded(QScreen *screen)

This signal is emitted whenever a new screen screen has been added to the system.

See also screens(), primaryScreen, and screenRemoved().

### `[static]` QScreen *QGuiApplication::screenAt(const QPoint &point)

Returns the screen at point, or `nullptr` if outside of any screen.

The point is in relation to the virtualGeometry() of each set of virtual siblings. If the point maps to more than one set of virtual siblings the first match is returned. If you wish to search only the virtual desktop siblings of a known screen (for example siblings of the screen of your application window `QWidget::windowHandle()->screen()`), use QScreen::virtualSiblingAt().

### `[signal]` void QGuiApplication::screenRemoved(QScreen *screen)

This signal is emitted whenever a screen is removed from the system. It provides an opportunity to manage the windows on the screen before Qt falls back to moving them to the primary screen.

See also screens(), screenAdded(), QObject::destroyed(), and QWindow::setScreen().

### `[static]` QList<QScreen *> QGuiApplication::screens()

Returns a list of all the screens associated with the windowing system the application is connected to.

### QString QGuiApplication::sessionId() const

Returns the current session's identifier.

If the application has been restored from an earlier session, this identifier is the same as it was in that previous session. The session identifier is guaranteed to be unique both for different applications and for different instances of the same application.

See also isSessionRestored(), sessionKey(), commitDataRequest(), and saveStateRequest().

### QString QGuiApplication::sessionKey() const

Returns the session key in the current session.

If the application has been restored from an earlier session, this key is the same as it was when the previous session ended.

The session key changes every time the session is saved. If the shutdown process is cancelled, another session key will be used when shutting down again.

See also isSessionRestored(), sessionId(), commitDataRequest(), and saveStateRequest().

### `[slot, since 6.5]` void QGuiApplication::setBadgeNumber(qint64 number)

Sets the application's badge to number.

Useful for providing feedback to the user about the number of unread messages or similar.

The badge will be overlaid on the application's icon in the Dock on macOS, the home screen icon on iOS, or the task bar on Windows and Linux.

If the number is outside the range supported by the platform, the number will be clamped to the supported range. If the number does not fit within the badge, the number may be visually elided.

Setting the number to 0 will clear the badge.

This function was introduced in Qt 6.5.

See also applicationName.

### `[static]` void QGuiApplication::setDesktopSettingsAware(bool on)

Sets whether Qt should use the system's standard colors, fonts, etc., to on. By default, this is `true`.

This function must be called before creating the QGuiApplication object, like this:

     int main(int argc, char *argv[])
     {
         QApplication::setDesktopSettingsAware(false);
         QApplication app(argc, argv);
         // ...
         return app.exec();
     }

See also desktopSettingsAware().

### `[static]` void QGuiApplication::setFont(const QFont &font)

Changes the default application font to font.

See also font().

### `[static]` void QGuiApplication::setHighDpiScaleFactorRoundingPolicy(Qt::HighDpiScaleFactorRoundingPolicy policy)

Sets the high-DPI scale factor rounding policy for the application. The policy decides how non-integer scale factors (such as Windows 150%) are handled.

The two principal options are whether fractional scale factors should be rounded to an integer or not. Keeping the scale factor as-is will make the user interface size match the OS setting exactly, but may cause painting errors, for example with the Windows style.

If rounding is wanted, then which type of rounding should be decided next. Mathematically correct rounding is supported but may not give the best visual results: Consider if you want to render 1.5x as 1x ("small UI") or as 2x ("large UI"). See the Qt::HighDpiScaleFactorRoundingPolicy enum for a complete list of all options.

This function must be called before creating the application object. The QGuiApplication::highDpiScaleFactorRoundingPolicy() accessor will reflect the environment, if set.

The default value is Qt::HighDpiScaleFactorRoundingPolicy::PassThrough.

See also highDpiScaleFactorRoundingPolicy().

### `[static]` void QGuiApplication::setOverrideCursor(const QCursor &cursor)

Sets the application override cursor to cursor.

Application override cursors are intended for showing the user that the application is in a special state, for example during an operation that might take some time.

This cursor will be displayed in all the application's widgets until restoreOverrideCursor() or another setOverrideCursor() is called.

Application cursors are stored on an internal stack. setOverrideCursor() pushes the cursor onto the stack, and restoreOverrideCursor() pops the active cursor off the stack. changeOverrideCursor() changes the currently active application override cursor.

Every setOverrideCursor() must eventually be followed by a corresponding restoreOverrideCursor(), otherwise the stack will never be emptied.

Example:

     QGuiApplication::setOverrideCursor(QCursor(Qt::WaitCursor));
     calculateHugeMandelbrot();              // lunch time...
     QGuiApplication::restoreOverrideCursor();

See also overrideCursor(), restoreOverrideCursor(), changeOverrideCursor(), and QWidget::setCursor().

### `[static]` void QGuiApplication::setPalette(const QPalette &pal)

Changes the application palette to pal.

The color roles from this palette are combined with the system's platform theme to form the application's final palette.

See also palette().

### `[static]` QStyleHints *QGuiApplication::styleHints()

Returns the application's style hints.

The style hints encapsulate a set of platform dependent properties such as double click intervals, full width selection and others.

The hints can be used to integrate tighter with the underlying platform.

See also QStyleHints.

### `[static]` void QGuiApplication::sync()

Function that can be used to sync Qt state with the Window Systems state.

This function will first empty Qts events by calling QCoreApplication::processEvents(), then the platform plugin will sync up with the windowsystem, and finally Qts events will be delived by another call to QCoreApplication::processEvents();

This function is timeconsuming and its use is discouraged.

### `[static]` QWindow *QGuiApplication::topLevelAt(const QPoint &pos)

Returns the top level window at the given position pos, if any.

### `[static]` QWindowList QGuiApplication::topLevelWindows()

Returns a list of the top-level windows in the application.

See also allWindows().

## Macro Documentation

### qGuiApp

A global pointer referring to the unique application object. Only valid for use when that object is a QGuiApplication.

See also QCoreApplication::instance() and qApp.