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QIcon Class

The QIcon class provides scalable icons in different modes and states. More...

Header: #include <QIcon>
qmake: QT += gui

Public Types

enum Mode { Normal, Disabled, Active, Selected }
enum State { Off, On }

Public Functions

QIcon()
QIcon(const QPixmap &pixmap)
QIcon(const QIcon &other)
QIcon(QIcon &&other)
QIcon(const QString &fileName)
QIcon(QIconEngine *engine)
~QIcon()
QSize actualSize(const QSize &size, Mode mode = Normal, State state = Off) const
QSize actualSize(QWindow *window, const QSize &size, Mode mode = Normal, State state = Off) const
void addFile(const QString &fileName, const QSize &size = QSize(), Mode mode = Normal, State state = Off)
void addPixmap(const QPixmap &pixmap, Mode mode = Normal, State state = Off)
QList<QSize> availableSizes(Mode mode = Normal, State state = Off) const
qint64 cacheKey() const
bool isMask() const
bool isNull() const
QString name() const
void paint(QPainter *painter, const QRect &rect, Qt::Alignment alignment = Qt::AlignCenter, Mode mode = Normal, State state = Off) const
void paint(QPainter *painter, int x, int y, int w, int h, Qt::Alignment alignment = Qt::AlignCenter, Mode mode = Normal, State state = Off) const
QPixmap pixmap(const QSize &size, Mode mode = Normal, State state = Off) const
QPixmap pixmap(int w, int h, Mode mode = Normal, State state = Off) const
QPixmap pixmap(int extent, Mode mode = Normal, State state = Off) const
QPixmap pixmap(QWindow *window, const QSize &size, Mode mode = Normal, State state = Off) const
void setIsMask(bool isMask)
void swap(QIcon &other)
operator QVariant() const
QIcon &operator=(const QIcon &other)
QIcon &operator=(QIcon &&other)

Static Public Members

QIcon fromTheme(const QString &name)
QIcon fromTheme(const QString &name, const QIcon &fallback)
bool hasThemeIcon(const QString &name)
void setThemeName(const QString &name)
void setThemeSearchPaths(const QStringList &paths)
QString themeName()
QStringList themeSearchPaths()
QDataStream &operator<<(QDataStream &stream, const QIcon &icon)
QDataStream &operator>>(QDataStream &stream, QIcon &icon)

Detailed Description

The QIcon class provides scalable icons in different modes and states.

A QIcon can generate smaller, larger, active, and disabled pixmaps from the set of pixmaps it is given. Such pixmaps are used by Qt widgets to show an icon representing a particular action.

The simplest use of QIcon is to create one from a QPixmap file or resource, and then use it, allowing Qt to work out all the required icon styles and sizes. For example:

QToolButton *button = new QToolButton;
button->setIcon(QIcon("open.xpm"));

To undo a QIcon, simply set a null icon in its place:

button->setIcon(QIcon());

Use the QImageReader::supportedImageFormats() and QImageWriter::supportedImageFormats() functions to retrieve a complete list of the supported file formats.

When you retrieve a pixmap using pixmap(QSize, Mode, State), and no pixmap for this given size, mode and state has been added with addFile() or addPixmap(), then QIcon will generate one on the fly. This pixmap generation happens in a QIconEngineV2. The default engine scales pixmaps down if required, but never up, and it uses the current style to calculate a disabled appearance. By using custom icon engines, you can customize every aspect of generated icons. With QIconEnginePluginV2 it is possible to register different icon engines for different file suffixes, making it possible for third parties to provide additional icon engines to those included with Qt.

Note: Since Qt 4.2, an icon engine that supports SVG is included.

Making Classes that Use QIcon

If you write your own widgets that have an option to set a small pixmap, consider allowing a QIcon to be set for that pixmap. The Qt class QToolButton is an example of such a widget.

Provide a method to set a QIcon, and when you draw the icon, choose whichever pixmap is appropriate for the current state of your widget. For example:

void MyWidget::drawIcon(QPainter *painter, QPoint pos)
{
    QPixmap pixmap = icon.pixmap(QSize(22, 22),
                                   isEnabled() ? QIcon::Normal
                                               : QIcon::Disabled,
                                   isChecked() ? QIcon::On
                                               : QIcon::Off);
    painter->drawPixmap(pos, pixmap);
}

You might also make use of the Active mode, perhaps making your widget Active when the mouse is over the widget (see QWidget::enterEvent()), while the mouse is pressed pending the release that will activate the function, or when it is the currently selected item. If the widget can be toggled, the "On" mode might be used to draw a different icon.

QIcon

Note: QIcon needs a QGuiApplication instance before the icon is created.

See also GUI Design Handbook: Iconic Label and Icons Example.

Member Type Documentation

enum QIcon::Mode

This enum type describes the mode for which a pixmap is intended to be used. The currently defined modes are:

ConstantValueDescription
QIcon::Normal0Display the pixmap when the user is not interacting with the icon, but the functionality represented by the icon is available.
QIcon::Disabled1Display the pixmap when the functionality represented by the icon is not available.
QIcon::Active2Display the pixmap when the functionality represented by the icon is available and the user is interacting with the icon, for example, moving the mouse over it or clicking it.
QIcon::Selected3Display the pixmap when the item represented by the icon is selected.

enum QIcon::State

This enum describes the state for which a pixmap is intended to be used. The state can be:

ConstantValueDescription
QIcon::Off1Display the pixmap when the widget is in an "off" state
QIcon::On0Display the pixmap when the widget is in an "on" state

Member Function Documentation

QIcon::QIcon()

Constructs a null icon.

QIcon::QIcon(const QPixmap &pixmap)

Constructs an icon from a pixmap.

QIcon::QIcon(const QIcon &other)

Constructs a copy of other. This is very fast.

QIcon::QIcon(QIcon &&other)

Move-constructs a QIcon instance, making it point to the same object that other was pointing to.

QIcon::QIcon(const QString &fileName)

Constructs an icon from the file with the given fileName. The file will be loaded on demand.

If fileName contains a relative path (e.g. the filename only) the relevant file must be found relative to the runtime working directory.

The file name can be either refer to an actual file on disk or to one of the application's embedded resources. See the Resource System overview for details on how to embed images and other resource files in the application's executable.

Use the QImageReader::supportedImageFormats() and QImageWriter::supportedImageFormats() functions to retrieve a complete list of the supported file formats.

QIcon::QIcon(QIconEngine *engine)

Creates an icon with a specific icon engine. The icon takes ownership of the engine.

QIcon::~QIcon()

Destroys the icon.

QSize QIcon::actualSize(const QSize &size, Mode mode = Normal, State state = Off) const

Returns the actual size of the icon for the requested size, mode, and state. The result might be smaller than requested, but never larger. The returned size is in device-independent pixels (This is relevant for high-dpi pixmaps.)

See also pixmap() and paint().

QSize QIcon::actualSize(QWindow *window, const QSize &size, Mode mode = Normal, State state = Off) const

Returns the actual size of the icon for the requested window size, mode, and state.

The pixmap can be smaller than the requested size. The returned size is in device-independent pixels (This is relevant for high-dpi pixmaps.)

This function was introduced in Qt 5.1.

See also actualSize(), pixmap(), and paint().

void QIcon::addFile(const QString &fileName, const QSize &size = QSize(), Mode mode = Normal, State state = Off)

Adds an image from the file with the given fileName to the icon, as a specialization for size, mode and state. The file will be loaded on demand. Note: custom icon engines are free to ignore additionally added pixmaps.

If fileName contains a relative path (e.g. the filename only) the relevant file must be found relative to the runtime working directory.

The file name can be either refer to an actual file on disk or to one of the application's embedded resources. See the Resource System overview for details on how to embed images and other resource files in the application's executable.

Use the QImageReader::supportedImageFormats() and QImageWriter::supportedImageFormats() functions to retrieve a complete list of the supported file formats.

If a high resolution version of the image exists (identified by the suffix @2x on the base name), it is automatically loaded and added with the device pixel ratio set to a value of 2. This can be disabled by setting the environment variable QT_HIGHDPI_DISABLE_2X_IMAGE_LOADING (see QImageReader).

Note: When you add a non-empty filename to a QIcon, the icon becomes non-null, even if the file doesn't exist or points to a corrupt file.

See also addPixmap() and QPixmap::devicePixelRatio().

void QIcon::addPixmap(const QPixmap &pixmap, Mode mode = Normal, State state = Off)

Adds pixmap to the icon, as a specialization for mode and state.

Custom icon engines are free to ignore additionally added pixmaps.

See also addFile().

QList<QSize> QIcon::availableSizes(Mode mode = Normal, State state = Off) const

Returns a list of available icon sizes for the specified mode and state.

This function was introduced in Qt 4.5.

qint64 QIcon::cacheKey() const

Returns a number that identifies the contents of this QIcon object. Distinct QIcon objects can have the same key if they refer to the same contents.

The cacheKey() will change when the icon is altered via addPixmap() or addFile().

Cache keys are mostly useful in conjunction with caching.

This function was introduced in Qt 4.3.

See also QPixmap::cacheKey().

[static] QIcon QIcon::fromTheme(const QString &name)

Returns the QIcon corresponding to name in the current icon theme.

The latest version of the freedesktop icon specification and naming specification can be obtained here:

To fetch an icon from the current icon theme:

    QIcon undoicon = QIcon::fromTheme("edit-undo");

Note: By default, only X11 will support themed icons. In order to use themed icons on Mac and Windows, you will have to bundle a compliant theme in one of your themeSearchPaths() and set the appropriate themeName().

Note: Qt will make use of GTK's icon-theme.cache if present to speed up the lookup. These caches can be generated using gtk-update-icon-cache: https://developer.gnome.org/gtk3/stable/gtk-update-icon-cache.html.

This function was introduced in Qt 4.6.

See also themeName(), setThemeName(), and themeSearchPaths().

[static] QIcon QIcon::fromTheme(const QString &name, const QIcon &fallback)

This is an overloaded function.

Returns the QIcon corresponding to name in the current icon theme. If no such icon is found in the current theme fallback is returned instead.

If you want to provide a guaranteed fallback for platforms that do not support theme icons, you can use the second argument:

    QIcon undoicon = QIcon::fromTheme("edit-undo", QIcon(":/undo.png"));

[static] bool QIcon::hasThemeIcon(const QString &name)

Returns true if there is an icon available for name in the current icon theme, otherwise returns false.

This function was introduced in Qt 4.6.

See also themeSearchPaths(), fromTheme(), and setThemeName().

bool QIcon::isMask() const

Returns true if this icon has been marked as a mask image. Certain platforms render mask icons differently (for example, menu icons on macOS).

This function was introduced in Qt 5.6.

See also setIsMask().

bool QIcon::isNull() const

Returns true if the icon is empty; otherwise returns false.

An icon is empty if it has neither a pixmap nor a filename.

Note: Even a non-null icon might not be able to create valid pixmaps, eg. if the file does not exist or cannot be read.

QString QIcon::name() const

Returns the name used to create the icon, if available.

Depending on the way the icon was created, it may have an associated name. This is the case for icons created with fromTheme() or icons using a QIconEngine which supports the QIconEngineV2::IconNameHook.

This function was introduced in Qt 4.7.

See also fromTheme() and QIconEngine.

void QIcon::paint(QPainter *painter, const QRect &rect, Qt::Alignment alignment = Qt::AlignCenter, Mode mode = Normal, State state = Off) const

Uses the painter to paint the icon with specified alignment, required mode, and state into the rectangle rect.

See also actualSize() and pixmap().

void QIcon::paint(QPainter *painter, int x, int y, int w, int h, Qt::Alignment alignment = Qt::AlignCenter, Mode mode = Normal, State state = Off) const

This is an overloaded function.

Paints the icon into the rectangle QRect(x, y, w, h).

QPixmap QIcon::pixmap(const QSize &size, Mode mode = Normal, State state = Off) const

Returns a pixmap with the requested size, mode, and state, generating one if necessary. The pixmap might be smaller than requested, but never larger.

Setting the Qt::AA_UseHighDpiPixmaps application attribute enables this function to return pixmaps that are larger than the requested size. Such images will have a devicePixelRatio larger than 1.

See also actualSize() and paint().

QPixmap QIcon::pixmap(int w, int h, Mode mode = Normal, State state = Off) const

This is an overloaded function.

Returns a pixmap of size QSize(w, h). The pixmap might be smaller than requested, but never larger.

Setting the Qt::AA_UseHighDpiPixmaps application attribute enables this function to return pixmaps that are larger than the requested size. Such images will have a devicePixelRatio larger than 1.

QPixmap QIcon::pixmap(int extent, Mode mode = Normal, State state = Off) const

This is an overloaded function.

Returns a pixmap of size QSize(extent, extent). The pixmap might be smaller than requested, but never larger.

Setting the Qt::AA_UseHighDpiPixmaps application attribute enables this function to return pixmaps that are larger than the requested size. Such images will have a devicePixelRatio larger than 1.

QPixmap QIcon::pixmap(QWindow *window, const QSize &size, Mode mode = Normal, State state = Off) const

Returns a pixmap with the requested window size, mode, and state, generating one if necessary.

The pixmap can be smaller than the requested size. If window is on a high-dpi display the pixmap can be larger. In that case it will have a devicePixelRatio larger than 1.

This function was introduced in Qt 5.1.

See also actualSize() and paint().

void QIcon::setIsMask(bool isMask)

Indicate that this icon is a mask image(boolean isMask), and hence can potentially be modified based on where it's displayed.

This function was introduced in Qt 5.6.

See also isMask().

[static] void QIcon::setThemeName(const QString &name)

Sets the current icon theme to name.

The name should correspond to a directory name in the themeSearchPath() containing an index.theme file describing it's contents.

This function was introduced in Qt 4.6.

See also themeSearchPaths() and themeName().

[static] void QIcon::setThemeSearchPaths(const QStringList &paths)

Sets the search paths for icon themes to paths.

This function was introduced in Qt 4.6.

See also themeSearchPaths(), fromTheme(), and setThemeName().

void QIcon::swap(QIcon &other)

Swaps icon other with this icon. This operation is very fast and never fails.

This function was introduced in Qt 4.8.

[static] QString QIcon::themeName()

Returns the name of the current icon theme.

On X11, the current icon theme depends on your desktop settings. On other platforms it is not set by default.

This function was introduced in Qt 4.6.

See also setThemeName(), themeSearchPaths(), fromTheme(), and hasThemeIcon().

[static] QStringList QIcon::themeSearchPaths()

Returns the search paths for icon themes.

The default value will depend on the platform:

On X11, the search path will use the XDG_DATA_DIRS environment variable if available.

By default all platforms will have the resource directory :\icons as a fallback. You can use "rcc -project" to generate a resource file from your icon theme.

This function was introduced in Qt 4.6.

See also setThemeSearchPaths(), fromTheme(), and setThemeName().

QIcon::operator QVariant() const

Returns the icon as a QVariant.

QIcon &QIcon::operator=(const QIcon &other)

Assigns the other icon to this icon and returns a reference to this icon.

QIcon &QIcon::operator=(QIcon &&other)

Move-assigns other to this QIcon instance.

This function was introduced in Qt 5.2.

Related Non-Members

QDataStream &operator<<(QDataStream &stream, const QIcon &icon)

Writes the given icon to the given stream as a PNG image. If the icon contains more than one image, all images will be written to the stream. Note that writing the stream to a file will not produce a valid image file.

This function was introduced in Qt 4.2.

QDataStream &operator>>(QDataStream &stream, QIcon &icon)

Reads an image, or a set of images, from the given stream into the given icon.

This function was introduced in Qt 4.2.

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