QIcon Class

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.

There are two ways that QIcon supports high DPI icons: via addFile() and fromTheme().

addFile() is useful if you have your own custom directory structure and do not need to use the freedesktop.org Icon Theme Specification. Icons created via this approach use Qt's "@nx" high DPI syntax.

Using fromTheme() is necessary if you plan on following the Icon Theme Specification. To make QIcon use the high DPI version of an image, add an additional entry to the appropriate index.theme file:

[Icon Theme]
Name=Test
Comment=Test Theme

Directories=32x32/actions,32x32@2/actions

[32x32/actions]
Size=32
Context=Actions
Type=Fixed

# High DPI version of the entry above.
[32x32@2/actions]
Size=32
Scale=2
Type=Fixed

Your icon theme directory would then look something like this:

├── 32x32
│   └── actions
│       └── appointment-new.png
├── 32x32@2
│   └── actions
│       └── appointment-new.png
└── index.theme

See also Icons Example

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

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

Constructs a null icon.

Constructs an icon from a pixmap.

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 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.

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

Constructs a copy of other. This is very fast.

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

Destroys the icon.

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.)

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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 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).

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

Custom icon engines are free to ignore additionally added pixmaps.

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

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.

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Returns the fallback search paths for icons.

The default value will depend on the platform.

This function was introduced in Qt 5.11.

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Returns the name of the fallback icon theme.

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

This function was introduced in Qt 5.12.

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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:

• http://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html

• http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html

To fetch an icon from the current icon theme:

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

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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"));

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

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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.

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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.

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().

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

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This is an overloaded function.

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

Returns a pixmap with the requested size, mode, and state, generating one if necessary. The pixmap might be smaller than requested, but never larger, unless the device-pixel ratio of the returned pixmap is larger than 1.

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This is an overloaded function.

Returns a pixmap of size QSize(w, h). The pixmap might be smaller than requested, but never larger, unless the device-pixel ratio of the returned pixmap is larger than 1.

This is an overloaded function.

Returns a pixmap of size QSize(extent, extent). The pixmap might be smaller than requested, but never larger, unless the device-pixel ratio of the returned pixmap is larger than 1.

This is an overloaded function.

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

This function was introduced in Qt 6.0.

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Sets the fallback search paths for icons to paths.

QIcon::setFallbackSearchPaths(QIcon::fallbackSearchPaths() << "my/search/path");

This function was introduced in Qt 5.11.

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Sets the fallback icon theme to name.

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

This function was introduced in Qt 5.12.

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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.

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Sets the current icon theme to name.

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

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Sets the search paths for icon themes to paths.

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

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.

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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.

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Returns the icon as a QVariant.

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

Move-assigns other to this QIcon instance.

This function was introduced in Qt 5.2.

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.

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

[since 5.1] QSize QIcon::actualSize(QWindow *window, const QSize &size, QIcon::Mode mode = Normal, QIcon::State state = Off) const▲

[since 5.1] QPixmap QIcon::pixmap(QWindow *window, const QSize &size, QIcon::Mode mode = Normal, QIcon::State state = Off) const▲