Qt 5.6 | Qt Widgets | C++ Classes | QDesktopWidget

Qt 5.6.2 Reference Documentation

# QDesktopWidget Class

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

Header: | #include <QDesktopWidget>
qmake: | QT += widgets
Inherits: | QWidget

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

## Properties

- primaryScreen : const int
- screenCount : const int
- virtualDesktop : const bool

- 58 properties inherited from QWidget

## Public Functions

const QRect | availableGeometry(int screen = -1) const
const QRect | availableGeometry(const QWidget *widget) const
const QRect | availableGeometry(const QPoint &p) const
bool | isVirtualDesktop() const
int | primaryScreen() const
QWidget * | screen(int screen = -1)
int | screenCount() const
const QRect | screenGeometry(int screen = -1) const
const QRect | screenGeometry(const QWidget *widget) const
const QRect | screenGeometry(const QPoint &p) const
int | screenNumber(const QWidget *widget = Q_NULLPTR) const
int | screenNumber(const QPoint &point) const

- 211 public functions inherited from QWidget

## Signals

void | primaryScreenChanged()
void | resized(int screen)
void | screenCountChanged(int newCount)
void | workAreaResized(int screen)

- 3 signals inherited from QWidget

## Reimplemented Protected Functions

virtual void | resizeEvent(QResizeEvent *event)

- 35 protected functions inherited from QWidget

### Additional Inherited Members

- 19 public slots inherited from QWidget
- 5 static public members inherited from QWidget
- 35 protected functions inherited from QWidget
- 1 protected slot inherited from QWidget

## 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.

This class provides information about the user's desktop, such as its total size, number of screens, the geometry of each screen, and whether they are configured as separate desktops or a single virtual desktop.

Widgets provided by Qt use this class to place tooltips, menus and dialog boxes on the correct screen for their parent or application widgets. Applications can use this class to obtain information that can be used to save window positions, or to place child widgets and dialogs on one particular screen.

### Obtaining a Desktop Widget

The QApplication::desktop() function is used to get an instance of QDesktopWidget.

The widget's screenGeometry() function provides information about the geometry of the available screens with. The number of screens available is returned by screenCount, and the screenCountChanged() signal is emitted when screens are added or removed. The screen number that a particular point or widget is located in is returned by screenNumber().

### Screen Geometry

To obtain the dimensions of a particular screen, call the screenGeometry() function. On some desktop environments, not all of the screen is available for applications to use; for example, an application dock or menu bar may take up some space. Use the availableGeometry() function to obtain the available area for applications.

QDesktopWidget also 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 not be used for computing the size of a widget to be placed on one of the screens.

On systems that are configured to use the available screens as a single, large virtual desktop, the virtualDesktop property will be set to true. In this case, the widget's size is usually the size of the bounding rectangle of all the screens.

### Use of the Primary Screen

For an application, the screen where the main widget resides is the primary screen. This is stored in the primaryScreen property. 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.

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

See also QApplication and QApplication::desktop().

## Property Documentation

### primaryScreen : const int

This property holds the index of the screen that is configured to be the primary screen on the system.

Access functions:

int | primaryScreen() const

Notifier signal:

void | primaryScreenChanged()

### screenCount : const int

This property holds the number of screens currently available on the system.

This property was introduced in Qt 4.6.

Access functions:

int | screenCount() const

Notifier signal:

void | screenCountChanged(int newCount)

### virtualDesktop : const bool

This property holds 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.

Access functions:

bool | isVirtualDesktop() const

## Member Function Documentation

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

Returns the available geometry of the screen with index 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 macOS, or the task bar on Windows). The default screen is used if screen is -1.

See also screenNumber() and screenGeometry().

### const QRect QDesktopWidget::availableGeometry(const QWidget *widget) const

This is an overloaded function.

Returns the available geometry of the screen which contains widget.

See also screenGeometry().

### const QRect QDesktopWidget::availableGeometry(const QPoint &p) const

This is an overloaded function.

Returns the available geometry of the screen which contains p.

See also screenGeometry().

### `[signal]` void QDesktopWidget::primaryScreenChanged()

This signal is emitted whenever the primary screen changes.

Note: This doesn't mean the QDesktopWidget::primaryScreen index will necessarily be different, but now it will refer to the new primary screen.

This function was introduced in Qt 5.6.

Note: Notifier signal for property primaryScreen.

See also primaryScreen and screenGeometry().

### `[virtual protected]` void QDesktopWidget::resizeEvent(QResizeEvent *event)

Reimplemented from QWidget::resizeEvent().

### `[signal]` void QDesktopWidget::resized(int screen)

This signal is emitted when the size of screen changes.

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

Returns a widget that represents the screen with index 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 screen.

See also primaryScreen, screenCount, and virtualDesktop.

### `[signal]` void QDesktopWidget::screenCountChanged(int newCount)

This signal is emitted when the number of screens changes to newCount.

This function was introduced in Qt 4.6.

Note: Notifier signal for property screenCount.

See also screenCount.

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

Returns the geometry of the screen with index screen. The default screen is used if screen is -1.

See also screenNumber().

### const QRect QDesktopWidget::screenGeometry(const QWidget *widget) const

This is an overloaded function.

Returns the geometry of the screen which contains widget.

### const QRect QDesktopWidget::screenGeometry(const QPoint &p) const

This is an overloaded function.

Returns the geometry of the screen which contains p.

### int QDesktopWidget::screenNumber(const QWidget *widget = Q_NULLPTR) 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 function.

Returns the index of the screen that contains the point, or the screen which is the shortest distance from the point.

See also primaryScreen.

### `[signal]` void QDesktopWidget::workAreaResized(int screen)

This signal is emitted when the work area available on screen changes.