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For an application, one of the available screens is the primary screen, i.e. the screen where the main widget resides (see primaryScreen). All windows opened in the context of the application should be constrained to the boundaries of the primary screen; for example, it would be inconvenient if a dialog box popped up on a different screen, or split over two screens. The QDesktopWidget provides information about the geometry of the available screens with screenGeometry(). The number of screens available is returned by screenCount, and the screenCountChanged signal is emitted when screens are added or removed during runtime. The screen number that a particular point or widget is located in is returned by screenNumber(). Widgets provided by Qt use this class, for example, to place tooltips, menus and dialog boxes according to the parent or application widget. Applications can use this class to save window positions, or to place child widgets and dialogs on one particular screen. \img qdesktopwidget.png Managing Multiple Screens In the illustration above, Application One's primary screen is screen 0, and App Two's primary screen is screen 1. \target multiple screens note \note QDesktopWidget inherits the QWidget properties, width() and height(), which specify the size of the desktop. However, for desktops with multiple screens, the size of the desktop is the union of all the screen sizes, so width() and height() should \e not be used for computing the size of a widget to be placed on one of the screens. The correct width and height values are obtained using availableGeometry() or screenGeometry() for a particular screen. \sa QApplication, QApplication::desktop(), QX11Info::appRootWindow() */ /*! \fn QDesktopWidget::QDesktopWidget() \internal Creates the desktop widget. If the system supports a virtual desktop, this widget will have the size of the virtual desktop; otherwise this widget will have the size of the primary screen. Instead of using QDesktopWidget directly, use QApplication::desktop(). */ /*! \fn QDesktopWidget::~QDesktopWidget() \internal Destroys the desktop widget and frees any allocated resources. */ /*! \fn int QDesktopWidget::numScreens() const Returns the number of available screens. \obsolete This function is deprecated. Use screenCount instead. \sa primaryScreen */ /*! \fn QWidget *QDesktopWidget::screen(int screen) Returns a widget that represents the screen with index \a screen (a value of -1 means the default screen). If the system uses a virtual desktop, the returned widget will have the geometry of the entire virtual desktop; i.e., bounding every \a screen. \sa primaryScreen, screenCount, virtualDesktop */ /*! \fn const QRect QDesktopWidget::availableGeometry(int screen) const Returns the available geometry of the screen with index \a screen. What is available will be subrect of screenGeometry() based on what the platform decides is available (for example excludes the dock and menu bar on Mac OS X, or the task bar on Windows). The default screen is used if \a screen is -1. \sa screenNumber(), screenGeometry() */ /*! \fn const QRect QDesktopWidget::availableGeometry(const QWidget *widget) const \overload Returns the available geometry of the screen which contains \a widget. \sa screenGeometry() */ /*! \fn const QRect QDesktopWidget::availableGeometry(const QPoint &p) const \overload Returns the available geometry of the screen which contains \a p. \sa screenGeometry() */ /*! \fn const QRect QDesktopWidget::screenGeometry(int screen) const Returns the geometry of the screen with index \a screen. The default screen is used if \a screen is -1. \sa screenNumber() */ /*! \fn const QRect QDesktopWidget::screenGeometry(const QWidget *widget) const \overload Returns the geometry of the screen which contains \a widget. */ /*! \fn const QRect QDesktopWidget::screenGeometry(const QPoint &p) const \overload Returns the geometry of the screen which contains \a p. */ /*! \fn int QDesktopWidget::screenNumber(const QWidget *widget) const Returns the index of the screen that contains the largest part of \a widget, or -1 if the widget not on a screen. \sa primaryScreen */ /*! \fn int QDesktopWidget::screenNumber(const QPoint &point) const \overload Returns the index of the screen that contains the \a point, or the screen which is the shortest distance from the \a point. \sa primaryScreen */ /*! \fn void QDesktopWidget::resizeEvent(QResizeEvent *event) \reimp */ /*! \fn void QDesktopWidget::resized(int screen) This signal is emitted when the size of \a screen changes. */ /*! \fn void QDesktopWidget::workAreaResized(int screen) This signal is emitted when the work area available on \a screen changes. */ /*! \property QDesktopWidget::screenCount \brief the number of screens currently available on the system. \since 4.6 \sa screenCountChanged() */ /*! \property QDesktopWidget::primaryScreen \brief the index of the screen that is configured to be the primary screen on the system. */ /*! \property QDesktopWidget::virtualDesktop \brief if the system manages the available screens in a virtual desktop. For virtual desktops, screen() will always return the same widget. The size of the virtual desktop is the size of this desktop widget. */ /*! \fn void QDesktopWidget::screenCountChanged(int newCount) \since 4.6 This signal is emitted when the number of screens changes to \a newCount. \sa screenCount */