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# QDesktopWidget Class Reference

The QDesktopWidget class provides access to screen information on multi-head systems. More...

`#include <qdesktopwidget.h>`

Inherits QWidget.

List of all member functions.

## Public Members

- QDesktopWidget ()
- ~QDesktopWidget ()
- bool isVirtualDesktop () const
- int numScreens () const
- int primaryScreen () const
- int screenNumber ( QWidget * widget = 0 ) const
- int screenNumber ( const QPoint & point ) const
- QWidget * screen ( int screen = -1 )
- const QRect & screenGeometry ( int screen = -1 ) const

## Detailed Description

The QDesktopWidget class provides access to screen information on multi-head systems.

Systems with more than one graphics card and monitor can manage the physical screen space available either as multiple desktops, or as a large virtual desktop, which usually has the size of the bounding rectangle of all the screens (see isVirtualDesktop()). 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 have to 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 numScreens(). 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 on one screen.

In the illustration above, Application One's primary screen is screen 0, and App Two's primary screen is screen 1.

See also Advanced Widgets and Environment Classes.

## Member Function Documentation

### QDesktopWidget::QDesktopWidget ()

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 QAppliation::desktop().

### QDesktopWidget::~QDesktopWidget ()

Destroy the object and free allocated resources.

### bool QDesktopWidget::isVirtualDesktop () const

Returns TRUE if the system manages the available screens in a virtual desktop; otherwise returns FALSE.

For virtual desktops, screen() will always return the same widget. The size of the virtual desktop is the size of this desktop widget.

### int QDesktopWidget::numScreens () const

Returns the number of available screens.

See also primaryScreen().

### int QDesktopWidget::primaryScreen () const

Returns the index of the primary screen.

See also numScreens().

### QWidget * QDesktopWidget::screen ( int screen = -1 )

Returns a widget that represents the screen with index screen. This widget can be used to draw directly on the desktop, using an unclipped painter like this:

      QPainter paint( QApplication::desktop()->screen( 0 ), TRUE );
      paint.draw...
      ...
      paint.end();

If the system uses a virtual desktop, the returned widget will have the geometry of the entire virtual desktop i.e. bounding every screen.

See also primaryScreen(), numScreens() and isVirtualDesktop().

### const QRect & QDesktopWidget::screenGeometry ( int screen = -1 ) const

Returns the geometry of the screen with index screen.

See also screenNumber().

### int QDesktopWidget::screenNumber ( QWidget * widget = 0 ) const

Returns the index of the screen that contains the largest part of widget, or -1 if the widget not on a screen.

See also primaryScreen().

### int QDesktopWidget::screenNumber ( const QPoint & point ) const

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns the index of the screen that contains point, or -1 if no screen contains the point.

See also primaryScreen().

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