GI.Gtk.Objects.Label

The Label widget displays a small amount of text. As the name implies, most labels are used to label another widget such as a Button, a MenuItem, or a ComboBox.

CSS nodes

plain code

label
├── [selection]
├── [link]
┊
╰── [link]

GtkLabel has a single CSS node with the name label. A wide variety of style classes may be applied to labels, such as .title, .subtitle, .dim-label, etc. In the ShortcutsWindow, labels are used wth the .keycap style class.

If the label has a selection, it gets a subnode with name selection.

If the label has links, there is one subnode per link. These subnodes carry the link or visited state depending on whether they have been visited.

GtkLabel as GtkBuildable

The GtkLabel implementation of the GtkBuildable interface supports a custom <attributes> element, which supports any number of <attribute> elements. The <attribute> element has attributes named “name“, “value“, “start“ and “end“ and allows you to specify Attribute values for this label.

An example of a UI definition fragment specifying Pango attributes: > >class="GtkLabel" > attributes > name="weight" value="PANGO_WEIGHT_BOLD"/ > name="background" value="red" start="5" end="10"/ > /attributes >/object

The start and end attributes specify the range of characters to which the Pango attribute applies. If start and end are not specified, the attribute is applied to the whole text. Note that specifying ranges does not make much sense with translatable attributes. Use markup embedded in the translatable content instead.

Mnemonics

Labels may contain “mnemonics”. Mnemonics are underlined characters in the label, used for keyboard navigation. Mnemonics are created by providing a string with an underscore before the mnemonic character, such as "_File", to the functions labelNewWithMnemonic or labelSetTextWithMnemonic.

Mnemonics automatically activate any activatable widget the label is inside, such as a Button; if the label is not inside the mnemonic’s target widget, you have to tell the label about the target using labelSetMnemonicWidget. Here’s a simple example where the label is inside a button:

C code

 // Pressing Alt+H will activate this button
 GtkWidget *button = gtk_button_new ();
 GtkWidget *label = gtk_label_new_with_mnemonic ("_Hello");
 gtk_container_add (GTK_CONTAINER (button), label);

There’s a convenience function to create buttons with a mnemonic label already inside:

C code

 // Pressing Alt+H will activate this button
 GtkWidget *button = gtk_button_new_with_mnemonic ("_Hello");

To create a mnemonic for a widget alongside the label, such as a Entry, you have to point the label at the entry with labelSetMnemonicWidget:

C code

 // Pressing Alt+H will focus the entry
 GtkWidget *entry = gtk_entry_new ();
 GtkWidget *label = gtk_label_new_with_mnemonic ("_Hello");
 gtk_label_set_mnemonic_widget (GTK_LABEL (label), entry);

Markup (styled text)

To make it easy to format text in a label (changing colors, fonts, etc.), label text can be provided in a simple [markup format][PangoMarkupFormat].

Here’s how to create a label with a small font:

C code

 GtkWidget *label = gtk_label_new (NULL);
 gtk_label_set_markup (GTK_LABEL (label), "<small>Small text</small>");

(See [complete documentation][PangoMarkupFormat] of available tags in the Pango manual.)

The markup passed to labelSetMarkup must be valid; for example, literal <, > and & characters must be escaped as &lt;, &gt;, and &amp;. If you pass text obtained from the user, file, or a network to labelSetMarkup, you’ll want to escape it with markupEscapeText or g_markup_printf_escaped().

Markup strings are just a convenient way to set the AttrList on a label; labelSetAttributes may be a simpler way to set attributes in some cases. Be careful though; AttrList tends to cause internationalization problems, unless you’re applying attributes to the entire string (i.e. unless you set the range of each attribute to [0, G_MAXINT)). The reason is that specifying the start_index and end_index for a Attribute requires knowledge of the exact string being displayed, so translations will cause problems.

Selectable labels

Labels can be made selectable with labelSetSelectable. Selectable labels allow the user to copy the label contents to the clipboard. Only labels that contain useful-to-copy information — such as error messages — should be made selectable.

{label-text-layout}

A label can contain any number of paragraphs, but will have performance problems if it contains more than a small number. Paragraphs are separated by newlines or other paragraph separators understood by Pango.

Labels can automatically wrap text if you call labelSetLineWrap.

labelSetJustify sets how the lines in a label align with one another. If you want to set how the label as a whole aligns in its available space, see the Widget:halign and Widget:valign properties.

The Label:width-chars and Label:max-width-chars properties can be used to control the size allocation of ellipsized or wrapped labels. For ellipsizing labels, if either is specified (and less than the actual text size), it is used as the minimum width, and the actual text size is used as the natural width of the label. For wrapping labels, width-chars is used as the minimum width, if specified, and max-width-chars is used as the natural width. Even if max-width-chars specified, wrapping labels will be rewrapped to use all of the available width.

Note that the interpretation of Label:width-chars and Label:max-width-chars has changed a bit with the introduction of [width-for-height geometry management.][geometry-management]

Links

Since 2.18, GTK+ supports markup for clickable hyperlinks in addition to regular Pango markup. The markup for links is borrowed from HTML, using the <a> with “href“ and “title“ attributes. GTK+ renders links similar to the way they appear in web browsers, with colored, underlined text. The “title“ attribute is displayed as a tooltip on the link.

An example looks like this:

C code

const gchar *text =
"Go to the"
"<a href=\"http://www.gtk.org title=\"&lt;i&gt;Our&lt;/i&gt; website\">"
"GTK+ website</a> for more...";
GtkWidget *label = gtk_label_new (NULL);
gtk_label_set_markup (GTK_LABEL (label), text);

It is possible to implement custom handling for links and their tooltips with the Label::activate-link signal and the labelGetCurrentUri function.

Exported types

newtype Label

Memory-managed wrapper type.

Constructors

Label (ManagedPtr Label)

Instances

GObject Label

Defined in GI.Gtk.Objects.Label

Methods

gobjectType :: Label -> IO GType

IsImplementorIface Label

Defined in GI.Gtk.Objects.Label

IsObject Label

Defined in GI.Gtk.Objects.Label

IsBuildable Label

Defined in GI.Gtk.Objects.Label

IsLabel Label

Defined in GI.Gtk.Objects.Label

IsMisc Label

Defined in GI.Gtk.Objects.Label

IsWidget Label

Defined in GI.Gtk.Objects.Label

class GObject o => IsLabel o

Type class for types which can be safely cast to Label, for instance with toLabel.

Instances

(GObject a, (UnknownAncestorError Label a :: Constraint)) => IsLabel a

Defined in GI.Gtk.Objects.Label

IsLabel Label

Defined in GI.Gtk.Objects.Label

IsLabel AccelLabel

Defined in GI.Gtk.Objects.AccelLabel

toLabel :: (MonadIO m, IsLabel o) => o -> m Label

Cast to Label, for types for which this is known to be safe. For general casts, use castTo.

noLabel :: Maybe Label

A convenience alias for Nothing :: Maybe Label.

Methods

getAngle

labelGetAngle

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Double

Returns: the angle of rotation for the label

Gets the angle of rotation for the label. See labelSetAngle.

Since: 2.6

getAttributes

labelGetAttributes

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m (Maybe AttrList)

Returns: the attribute list, or Nothing if none was set.

Gets the attribute list that was set on the label using labelSetAttributes, if any. This function does not reflect attributes that come from the labels markup (see labelSetMarkup). If you want to get the effective attributes for the label, use pango_layout_get_attribute (gtk_label_get_layout (label)).

getCurrentUri

labelGetCurrentUri

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Text

Returns: the currently active URI. The string is owned by GTK+ and must not be freed or modified.

Returns the URI for the currently active link in the label. The active link is the one under the mouse pointer or, in a selectable label, the link in which the text cursor is currently positioned.

This function is intended for use in a Label::activate-link handler or for use in a Widget::query-tooltip handler.

Since: 2.18

getEllipsize

labelGetEllipsize

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m EllipsizeMode

Returns: EllipsizeMode

Returns the ellipsizing position of the label. See labelSetEllipsize.

Since: 2.6

getJustify

labelGetJustify

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Justification

Returns: Justification

Returns the justification of the label. See labelSetJustify.

getLabel

labelGetLabel

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Text

Returns: the text of the label widget. This string is owned by the widget and must not be modified or freed.

Fetches the text from a label widget including any embedded underlines indicating mnemonics and Pango markup. (See labelGetText).

getLayout

labelGetLayout

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Layout

Returns: the Layout for this label

Gets the Layout used to display the label. The layout is useful to e.g. convert text positions to pixel positions, in combination with labelGetLayoutOffsets. The returned layout is owned by the label so need not be freed by the caller. The label is free to recreate its layout at any time, so it should be considered read-only.

getLayoutOffsets

labelGetLayoutOffsets

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m (Int32, Int32)

Obtains the coordinates where the label will draw the Layout representing the text in the label; useful to convert mouse events into coordinates inside the Layout, e.g. to take some action if some part of the label is clicked. Of course you will need to create a EventBox to receive the events, and pack the label inside it, since labels are windowless (they return False from widgetGetHasWindow). Remember when using the Layout functions you need to convert to and from pixels using PANGO_PIXELS() or SCALE.

getLineWrap

labelGetLineWrap

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True if the lines of the label are automatically wrapped.

Returns whether lines in the label are automatically wrapped. See labelSetLineWrap.

getLineWrapMode

labelGetLineWrapMode

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m WrapMode

Returns: True if the lines of the label are automatically wrapped.

Returns line wrap mode used by the label. See labelSetLineWrapMode.

Since: 2.10

getLines

labelGetLines

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Int32

Returns: The number of lines

Gets the number of lines to which an ellipsized, wrapping label should be limited. See labelSetLines.

Since: 3.10

getMaxWidthChars

labelGetMaxWidthChars

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Int32

Returns: the maximum width of the label in characters.

Retrieves the desired maximum width of label, in characters. See labelSetWidthChars.

Since: 2.6

getMnemonicKeyval

labelGetMnemonicKeyval

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Word32

Returns: GDK keyval usable for accelerators, or KEY_VoidSymbol

If the label has been set so that it has an mnemonic key this function returns the keyval used for the mnemonic accelerator. If there is no mnemonic set up it returns KEY_VoidSymbol.

getMnemonicWidget

labelGetMnemonicWidget

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m (Maybe Widget)

Returns: the target of the label’s mnemonic, or Nothing if none has been set and the default algorithm will be used.

Retrieves the target of the mnemonic (keyboard shortcut) of this label. See labelSetMnemonicWidget.

getSelectable

labelGetSelectable

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True if the user can copy text from the label

Gets the value set by labelSetSelectable.

getSelectionBounds

labelGetSelectionBounds

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m (Bool, Int32, Int32)

Returns: True if selection is non-empty

Gets the selected range of characters in the label, returning True if there’s a selection.

getSingleLineMode

labelGetSingleLineMode

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True when the label is in single line mode.

Returns whether the label is in single line mode.

Since: 2.6

getText

labelGetText

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Text

Returns: the text in the label widget. This is the internal string used by the label, and must not be modified.

Fetches the text from a label widget, as displayed on the screen. This does not include any embedded underlines indicating mnemonics or Pango markup. (See labelGetLabel)

getTrackVisitedLinks

labelGetTrackVisitedLinks

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True if clicked links are remembered

Returns whether the label is currently keeping track of clicked links.

Since: 2.18

getUseMarkup

labelGetUseMarkup

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True if the label’s text will be parsed for markup.

Returns whether the label’s text is interpreted as marked up with the [Pango text markup language][PangoMarkupFormat]. See gtk_label_set_use_markup ().

getUseUnderline

labelGetUseUnderline

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Bool

Returns: True whether an embedded underline in the label indicates the mnemonic accelerator keys.

Returns whether an embedded underline in the label indicates a mnemonic. See labelSetUseUnderline.

getWidthChars

labelGetWidthChars

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Int32

Returns: the width of the label in characters.

Retrieves the desired width of label, in characters. See labelSetWidthChars.

Since: 2.6

getXalign

labelGetXalign

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Float

Returns: the xalign property

Gets the Label:xalign property for label.

Since: 3.16

getYalign

labelGetYalign

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> m Float

Returns: the yalign property

Gets the Label:yalign property for label.

Since: 3.16

new

labelNew

Arguments

:: (HasCallStack, MonadIO m)

=> Maybe Text

str: The text of the label

-> m Label

Returns: the new Label

Creates a new label with the given text inside it. You can pass Nothing to get an empty label widget.

newWithMnemonic

labelNewWithMnemonic

Arguments

:: (HasCallStack, MonadIO m)

=> Maybe Text

str: The text of the label, with an underscore in front of the mnemonic character

-> m Label

Returns: the new Label

Creates a new Label, containing the text in str.

If characters in str are preceded by an underscore, they are underlined. If you need a literal underscore character in a label, use '__' (two underscores). The first underlined character represents a keyboard accelerator called a mnemonic. The mnemonic key can be used to activate another widget, chosen automatically, or explicitly using labelSetMnemonicWidget.

If labelSetMnemonicWidget is not called, then the first activatable ancestor of the Label will be chosen as the mnemonic widget. For instance, if the label is inside a button or menu item, the button or menu item will automatically become the mnemonic widget and be activated by the mnemonic.

selectRegion

labelSelectRegion

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Int32

startOffset: start offset (in characters not bytes)

-> Int32

endOffset: end offset (in characters not bytes)

-> m ()

Selects a range of characters in the label, if the label is selectable. See labelSetSelectable. If the label is not selectable, this function has no effect. If startOffset or endOffset are -1, then the end of the label will be substituted.

setAngle

labelSetAngle

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Double

angle: the angle that the baseline of the label makes with the horizontal, in degrees, measured counterclockwise

-> m ()

Sets the angle of rotation for the label. An angle of 90 reads from from bottom to top, an angle of 270, from top to bottom. The angle setting for the label is ignored if the label is selectable, wrapped, or ellipsized.

Since: 2.6

setAttributes

labelSetAttributes

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Maybe AttrList

attrs: a AttrList, or Nothing

-> m ()

Sets a AttrList; the attributes in the list are applied to the label text.

The attributes set with this function will be applied and merged with any other attributes previously effected by way of the Label:use-underline or Label:use-markup properties. While it is not recommended to mix markup strings with manually set attributes, if you must; know that the attributes will be applied to the label after the markup string is parsed.

setEllipsize

labelSetEllipsize

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> EllipsizeMode

mode: a EllipsizeMode

-> m ()

Sets the mode used to ellipsize (add an ellipsis: "...") to the text if there is not enough space to render the entire string.

Since: 2.6

setJustify

labelSetJustify

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Justification

jtype: a Justification

-> m ()

Sets the alignment of the lines in the text of the label relative to each other. JustificationLeft is the default value when the widget is first created with labelNew. If you instead want to set the alignment of the label as a whole, use widgetSetHalign instead. labelSetJustify has no effect on labels containing only a single line.

setLabel

labelSetLabel

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Text

str: the new text to set for the label

-> m ()

Sets the text of the label. The label is interpreted as including embedded underlines and/or Pango markup depending on the values of the Label:use-underline and Label:use-markup properties.

setLineWrap

labelSetLineWrap

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

wrap: the setting

-> m ()

Toggles line wrapping within the Label widget. True makes it break lines if text exceeds the widget’s size. False lets the text get cut off by the edge of the widget if it exceeds the widget size.

Note that setting line wrapping to True does not make the label wrap at its parent container’s width, because GTK+ widgets conceptually can’t make their requisition depend on the parent container’s size. For a label that wraps at a specific position, set the label’s width using widgetSetSizeRequest.

setLineWrapMode

labelSetLineWrapMode

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> WrapMode

wrapMode: the line wrapping mode

-> m ()

If line wrapping is on (see labelSetLineWrap) this controls how the line wrapping is done. The default is WrapModeWord which means wrap on word boundaries.

Since: 2.10

setLines

labelSetLines

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Int32

lines: the desired number of lines, or -1

-> m ()

Sets the number of lines to which an ellipsized, wrapping label should be limited. This has no effect if the label is not wrapping or ellipsized. Set this to -1 if you don’t want to limit the number of lines.

Since: 3.10

setMarkup

labelSetMarkup

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Text

str: a markup string (see [Pango markup format][PangoMarkupFormat])

-> m ()

Parses str which is marked up with the [Pango text markup language][PangoMarkupFormat], setting the label’s text and attribute list based on the parse results.

If the str is external data, you may need to escape it with markupEscapeText or g_markup_printf_escaped():

C code

GtkWidget *label = gtk_label_new (NULL);
const char *str = "some text";
const char *format = "<span style=\"italic\">\%s</span>";
char *markup;

markup = g_markup_printf_escaped (format, str);
gtk_label_set_markup (GTK_LABEL (label), markup);
g_free (markup);

This function will set the Label:use-markup property to True as a side effect.

If you set the label contents using the Label:label property you should also ensure that you set the Label:use-markup property accordingly.

See also: labelSetText

setMarkupWithMnemonic

labelSetMarkupWithMnemonic

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Text

str: a markup string (see [Pango markup format][PangoMarkupFormat])

-> m ()

Parses str which is marked up with the [Pango text markup language][PangoMarkupFormat], setting the label’s text and attribute list based on the parse results. If characters in str are preceded by an underscore, they are underlined indicating that they represent a keyboard accelerator called a mnemonic.

The mnemonic key can be used to activate another widget, chosen automatically, or explicitly using labelSetMnemonicWidget.

setMaxWidthChars

labelSetMaxWidthChars

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Int32

nChars: the new desired maximum width, in characters.

-> m ()

Sets the desired maximum width in characters of label to nChars.

Since: 2.6

setMnemonicWidget

labelSetMnemonicWidget

Arguments

:: (HasCallStack, MonadIO m, IsLabel a, IsWidget b)

=> a

label: a Label

-> Maybe b

widget: the target Widget, or Nothing to unset

-> m ()

If the label has been set so that it has an mnemonic key (using i.e. labelSetMarkupWithMnemonic, labelSetTextWithMnemonic, labelNewWithMnemonic or the “use_underline” property) the label can be associated with a widget that is the target of the mnemonic. When the label is inside a widget (like a Button or a Notebook tab) it is automatically associated with the correct widget, but sometimes (i.e. when the target is a Entry next to the label) you need to set it explicitly using this function.

The target widget will be accelerated by emitting the GtkWidget::mnemonic-activate signal on it. The default handler for this signal will activate the widget if there are no mnemonic collisions and toggle focus between the colliding widgets otherwise.

setPattern

labelSetPattern

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: The Label you want to set the pattern to.

-> Text

pattern: The pattern as described above.

-> m ()

The pattern of underlines you want under the existing text within the Label widget. For example if the current text of the label says “FooBarBaz” passing a pattern of “_ _” will underline “Foo” and “Baz” but not “Bar”.

setSelectable

labelSetSelectable

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

setting: True to allow selecting text in the label

-> m ()

Selectable labels allow the user to select text from the label, for copy-and-paste.

setSingleLineMode

labelSetSingleLineMode

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

singleLineMode: True if the label should be in single line mode

-> m ()

Sets whether the label is in single line mode.

Since: 2.6

setText

labelSetText

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Text

str: The text you want to set

-> m ()

Sets the text within the Label widget. It overwrites any text that was there before.

This function will clear any previously set mnemonic accelerators, and set the Label:use-underline property to False as a side effect.

This function will set the Label:use-markup property to False as a side effect.

See also: labelSetMarkup

setTextWithMnemonic

labelSetTextWithMnemonic

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Text

str: a string

-> m ()

Sets the label’s text from the string str. If characters in str are preceded by an underscore, they are underlined indicating that they represent a keyboard accelerator called a mnemonic. The mnemonic key can be used to activate another widget, chosen automatically, or explicitly using labelSetMnemonicWidget.

setTrackVisitedLinks

labelSetTrackVisitedLinks

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

trackLinks: True to track visited links

-> m ()

Sets whether the label should keep track of clicked links (and use a different color for them).

Since: 2.18

setUseMarkup

labelSetUseMarkup

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

setting: True if the label’s text should be parsed for markup.

-> m ()

Sets whether the text of the label contains markup in [Pango’s text markup language][PangoMarkupFormat]. See labelSetMarkup.

setUseUnderline

labelSetUseUnderline

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Bool

setting: True if underlines in the text indicate mnemonics

-> m ()

If true, an underline in the text indicates the next character should be used for the mnemonic accelerator key.

setWidthChars

labelSetWidthChars

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Int32

nChars: the new desired width, in characters.

-> m ()

Sets the desired width in characters of label to nChars.

Since: 2.6

setXalign

labelSetXalign

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Float

xalign: the new xalign value, between 0 and 1

-> m ()

Sets the Label:xalign property for label.

Since: 3.16

setYalign

labelSetYalign

Arguments

:: (HasCallStack, MonadIO m, IsLabel a)

=> a

label: a Label

-> Float

yalign: the new yalign value, between 0 and 1

-> m ()

Sets the Label:yalign property for label.

Since: 3.16

Properties

angle

The angle that the baseline of the label makes with the horizontal, in degrees, measured counterclockwise. An angle of 90 reads from from bottom to top, an angle of 270, from top to bottom. Ignored if the label is selectable.

Since: 2.6

constructLabelAngle :: IsLabel o => Double -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “angle” property. This is rarely needed directly, but it is used by new.

getLabelAngle :: (MonadIO m, IsLabel o) => o -> m Double

Get the value of the “angle” property. When overloading is enabled, this is equivalent to

get label #angle

setLabelAngle :: (MonadIO m, IsLabel o) => o -> Double -> m ()

Set the value of the “angle” property. When overloading is enabled, this is equivalent to

set label [ #angle := value ]

attributes

No description available in the introspection data.

clearLabelAttributes :: (MonadIO m, IsLabel o) => o -> m ()

Set the value of the “attributes” property to Nothing. When overloading is enabled, this is equivalent to

clear #attributes

constructLabelAttributes :: IsLabel o => AttrList -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “attributes” property. This is rarely needed directly, but it is used by new.

getLabelAttributes :: (MonadIO m, IsLabel o) => o -> m (Maybe AttrList)

Get the value of the “attributes” property. When overloading is enabled, this is equivalent to

get label #attributes

setLabelAttributes :: (MonadIO m, IsLabel o) => o -> AttrList -> m ()

Set the value of the “attributes” property. When overloading is enabled, this is equivalent to

set label [ #attributes := value ]

cursorPosition

No description available in the introspection data.

getLabelCursorPosition :: (MonadIO m, IsLabel o) => o -> m Int32

Get the value of the “cursor-position” property. When overloading is enabled, this is equivalent to

get label #cursorPosition

ellipsize

The preferred place to ellipsize the string, if the label does not have enough room to display the entire string, specified as a EllipsizeMode.

Note that setting this property to a value other than EllipsizeModeNone has the side-effect that the label requests only enough space to display the ellipsis "...". In particular, this means that ellipsizing labels do not work well in notebook tabs, unless the Notebook tab-expand child property is set to True. Other ways to set a label's width are widgetSetSizeRequest and labelSetWidthChars.

Since: 2.6

constructLabelEllipsize :: IsLabel o => EllipsizeMode -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “ellipsize” property. This is rarely needed directly, but it is used by new.

getLabelEllipsize :: (MonadIO m, IsLabel o) => o -> m EllipsizeMode

Get the value of the “ellipsize” property. When overloading is enabled, this is equivalent to

get label #ellipsize

setLabelEllipsize :: (MonadIO m, IsLabel o) => o -> EllipsizeMode -> m ()

Set the value of the “ellipsize” property. When overloading is enabled, this is equivalent to

set label [ #ellipsize := value ]

justify

No description available in the introspection data.

constructLabelJustify :: IsLabel o => Justification -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “justify” property. This is rarely needed directly, but it is used by new.

getLabelJustify :: (MonadIO m, IsLabel o) => o -> m Justification

Get the value of the “justify” property. When overloading is enabled, this is equivalent to

get label #justify

setLabelJustify :: (MonadIO m, IsLabel o) => o -> Justification -> m ()

Set the value of the “justify” property. When overloading is enabled, this is equivalent to

set label [ #justify := value ]

label

The contents of the label.

If the string contains [Pango XML markup][PangoMarkupFormat], you will have to set the Label:use-markup property to True in order for the label to display the markup attributes. See also labelSetMarkup for a convenience function that sets both this property and the Label:use-markup property at the same time.

If the string contains underlines acting as mnemonics, you will have to set the Label:use-underline property to True in order for the label to display them.

constructLabelLabel :: IsLabel o => Text -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “label” property. This is rarely needed directly, but it is used by new.

getLabelLabel :: (MonadIO m, IsLabel o) => o -> m Text

Get the value of the “label” property. When overloading is enabled, this is equivalent to

get label #label

setLabelLabel :: (MonadIO m, IsLabel o) => o -> Text -> m ()

Set the value of the “label” property. When overloading is enabled, this is equivalent to

set label [ #label := value ]

lines

The number of lines to which an ellipsized, wrapping label should be limited. This property has no effect if the label is not wrapping or ellipsized. Set this property to -1 if you don't want to limit the number of lines.

Since: 3.10

constructLabelLines :: IsLabel o => Int32 -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “lines” property. This is rarely needed directly, but it is used by new.

getLabelLines :: (MonadIO m, IsLabel o) => o -> m Int32

Get the value of the “lines” property. When overloading is enabled, this is equivalent to

get label #lines

setLabelLines :: (MonadIO m, IsLabel o) => o -> Int32 -> m ()

Set the value of the “lines” property. When overloading is enabled, this is equivalent to

set label [ #lines := value ]

maxWidthChars

The desired maximum width of the label, in characters. If this property is set to -1, the width will be calculated automatically.

See the section on [text layout][label-text-layout] for details of how Label:width-chars and Label:max-width-chars determine the width of ellipsized and wrapped labels.

Since: 2.6

constructLabelMaxWidthChars :: IsLabel o => Int32 -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “max-width-chars” property. This is rarely needed directly, but it is used by new.

getLabelMaxWidthChars :: (MonadIO m, IsLabel o) => o -> m Int32

Get the value of the “max-width-chars” property. When overloading is enabled, this is equivalent to

get label #maxWidthChars

setLabelMaxWidthChars :: (MonadIO m, IsLabel o) => o -> Int32 -> m ()

Set the value of the “max-width-chars” property. When overloading is enabled, this is equivalent to

set label [ #maxWidthChars := value ]

mnemonicKeyval

No description available in the introspection data.

getLabelMnemonicKeyval :: (MonadIO m, IsLabel o) => o -> m Word32

Get the value of the “mnemonic-keyval” property. When overloading is enabled, this is equivalent to

get label #mnemonicKeyval

mnemonicWidget

No description available in the introspection data.

clearLabelMnemonicWidget :: (MonadIO m, IsLabel o) => o -> m ()

Set the value of the “mnemonic-widget” property to Nothing. When overloading is enabled, this is equivalent to

clear #mnemonicWidget

constructLabelMnemonicWidget :: (IsLabel o, IsWidget a) => a -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “mnemonic-widget” property. This is rarely needed directly, but it is used by new.

getLabelMnemonicWidget :: (MonadIO m, IsLabel o) => o -> m (Maybe Widget)

Get the value of the “mnemonic-widget” property. When overloading is enabled, this is equivalent to

get label #mnemonicWidget

setLabelMnemonicWidget :: (MonadIO m, IsLabel o, IsWidget a) => o -> a -> m ()

Set the value of the “mnemonic-widget” property. When overloading is enabled, this is equivalent to

set label [ #mnemonicWidget := value ]

pattern

No description available in the introspection data.

constructLabelPattern :: IsLabel o => Text -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “pattern” property. This is rarely needed directly, but it is used by new.

setLabelPattern :: (MonadIO m, IsLabel o) => o -> Text -> m ()

Set the value of the “pattern” property. When overloading is enabled, this is equivalent to

set label [ #pattern := value ]

selectable

No description available in the introspection data.

constructLabelSelectable :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “selectable” property. This is rarely needed directly, but it is used by new.

getLabelSelectable :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “selectable” property. When overloading is enabled, this is equivalent to

get label #selectable

setLabelSelectable :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “selectable” property. When overloading is enabled, this is equivalent to

set label [ #selectable := value ]

selectionBound

No description available in the introspection data.

getLabelSelectionBound :: (MonadIO m, IsLabel o) => o -> m Int32

Get the value of the “selection-bound” property. When overloading is enabled, this is equivalent to

get label #selectionBound

singleLineMode

Whether the label is in single line mode. In single line mode, the height of the label does not depend on the actual text, it is always set to ascent + descent of the font. This can be an advantage in situations where resizing the label because of text changes would be distracting, e.g. in a statusbar.

Since: 2.6

constructLabelSingleLineMode :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “single-line-mode” property. This is rarely needed directly, but it is used by new.

getLabelSingleLineMode :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “single-line-mode” property. When overloading is enabled, this is equivalent to

get label #singleLineMode

setLabelSingleLineMode :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “single-line-mode” property. When overloading is enabled, this is equivalent to

set label [ #singleLineMode := value ]

trackVisitedLinks

Set this property to True to make the label track which links have been visited. It will then apply the GTK_STATE_FLAG_VISITED when rendering this link, in addition to GTK_STATE_FLAG_LINK.

Since: 2.18

constructLabelTrackVisitedLinks :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “track-visited-links” property. This is rarely needed directly, but it is used by new.

getLabelTrackVisitedLinks :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “track-visited-links” property. When overloading is enabled, this is equivalent to

get label #trackVisitedLinks

setLabelTrackVisitedLinks :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “track-visited-links” property. When overloading is enabled, this is equivalent to

set label [ #trackVisitedLinks := value ]

useMarkup

No description available in the introspection data.

constructLabelUseMarkup :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “use-markup” property. This is rarely needed directly, but it is used by new.

getLabelUseMarkup :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “use-markup” property. When overloading is enabled, this is equivalent to

get label #useMarkup

setLabelUseMarkup :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “use-markup” property. When overloading is enabled, this is equivalent to

set label [ #useMarkup := value ]

useUnderline

No description available in the introspection data.

constructLabelUseUnderline :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “use-underline” property. This is rarely needed directly, but it is used by new.

getLabelUseUnderline :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “use-underline” property. When overloading is enabled, this is equivalent to

get label #useUnderline

setLabelUseUnderline :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “use-underline” property. When overloading is enabled, this is equivalent to

set label [ #useUnderline := value ]

widthChars

The desired width of the label, in characters. If this property is set to -1, the width will be calculated automatically.

See the section on [text layout][label-text-layout] for details of how Label:width-chars and Label:max-width-chars determine the width of ellipsized and wrapped labels.

Since: 2.6

constructLabelWidthChars :: IsLabel o => Int32 -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “width-chars” property. This is rarely needed directly, but it is used by new.

getLabelWidthChars :: (MonadIO m, IsLabel o) => o -> m Int32

Get the value of the “width-chars” property. When overloading is enabled, this is equivalent to

get label #widthChars

setLabelWidthChars :: (MonadIO m, IsLabel o) => o -> Int32 -> m ()

Set the value of the “width-chars” property. When overloading is enabled, this is equivalent to

set label [ #widthChars := value ]

wrap

No description available in the introspection data.

constructLabelWrap :: IsLabel o => Bool -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “wrap” property. This is rarely needed directly, but it is used by new.

getLabelWrap :: (MonadIO m, IsLabel o) => o -> m Bool

Get the value of the “wrap” property. When overloading is enabled, this is equivalent to

get label #wrap

setLabelWrap :: (MonadIO m, IsLabel o) => o -> Bool -> m ()

Set the value of the “wrap” property. When overloading is enabled, this is equivalent to

set label [ #wrap := value ]

wrapMode

If line wrapping is on (see the Label:wrap property) this controls how the line wrapping is done. The default is WrapModeWord, which means wrap on word boundaries.

Since: 2.10

constructLabelWrapMode :: IsLabel o => WrapMode -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “wrap-mode” property. This is rarely needed directly, but it is used by new.

getLabelWrapMode :: (MonadIO m, IsLabel o) => o -> m WrapMode

Get the value of the “wrap-mode” property. When overloading is enabled, this is equivalent to

get label #wrapMode

setLabelWrapMode :: (MonadIO m, IsLabel o) => o -> WrapMode -> m ()

Set the value of the “wrap-mode” property. When overloading is enabled, this is equivalent to

set label [ #wrapMode := value ]

xalign

The xalign property determines the horizontal aligment of the label text inside the labels size allocation. Compare this to Widget:halign, which determines how the labels size allocation is positioned in the space available for the label.

Since: 3.16

constructLabelXalign :: IsLabel o => Float -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “xalign” property. This is rarely needed directly, but it is used by new.

getLabelXalign :: (MonadIO m, IsLabel o) => o -> m Float

Get the value of the “xalign” property. When overloading is enabled, this is equivalent to

get label #xalign

setLabelXalign :: (MonadIO m, IsLabel o) => o -> Float -> m ()

Set the value of the “xalign” property. When overloading is enabled, this is equivalent to

set label [ #xalign := value ]

yalign

The yalign property determines the vertical aligment of the label text inside the labels size allocation. Compare this to Widget:valign, which determines how the labels size allocation is positioned in the space available for the label.

Since: 3.16

constructLabelYalign :: IsLabel o => Float -> IO (GValueConstruct o)

Construct a GValueConstruct with valid value for the “yalign” property. This is rarely needed directly, but it is used by new.

getLabelYalign :: (MonadIO m, IsLabel o) => o -> m Float

Get the value of the “yalign” property. When overloading is enabled, this is equivalent to

get label #yalign

setLabelYalign :: (MonadIO m, IsLabel o) => o -> Float -> m ()

Set the value of the “yalign” property. When overloading is enabled, this is equivalent to

set label [ #yalign := value ]

Signals

activateCurrentLink

type C_LabelActivateCurrentLinkCallback = Ptr () -> Ptr () -> IO ()

Type for the callback on the (unwrapped) C side.

type LabelActivateCurrentLinkCallback = IO ()

A [keybinding signal][GtkBindingSignal] which gets emitted when the user activates a link in the label.

Applications may also emit the signal with g_signal_emit_by_name() if they need to control activation of URIs programmatically.

The default bindings for this signal are all forms of the Enter key.

Since: 2.18

afterLabelActivateCurrentLink :: (IsLabel a, MonadIO m) => a -> LabelActivateCurrentLinkCallback -> m SignalHandlerId

Connect a signal handler for the “activate-current-link” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after label #activateCurrentLink callback

genClosure_LabelActivateCurrentLink :: LabelActivateCurrentLinkCallback -> IO Closure

Wrap the callback into a Closure.

mk_LabelActivateCurrentLinkCallback :: C_LabelActivateCurrentLinkCallback -> IO (FunPtr C_LabelActivateCurrentLinkCallback)

Generate a function pointer callable from C code, from a C_LabelActivateCurrentLinkCallback.

noLabelActivateCurrentLinkCallback :: Maybe LabelActivateCurrentLinkCallback

A convenience synonym for Nothing :: Maybe LabelActivateCurrentLinkCallback.

onLabelActivateCurrentLink :: (IsLabel a, MonadIO m) => a -> LabelActivateCurrentLinkCallback -> m SignalHandlerId

Connect a signal handler for the “activate-current-link” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on label #activateCurrentLink callback

wrap_LabelActivateCurrentLinkCallback :: LabelActivateCurrentLinkCallback -> C_LabelActivateCurrentLinkCallback

Wrap a LabelActivateCurrentLinkCallback into a C_LabelActivateCurrentLinkCallback.

activateLink

type C_LabelActivateLinkCallback = Ptr () -> CString -> Ptr () -> IO CInt

Type for the callback on the (unwrapped) C side.

type LabelActivateLinkCallback

Arguments

 = Text

uri: the URI that is activated

-> IO Bool

Returns: True if the link has been activated

The signal which gets emitted to activate a URI. Applications may connect to it to override the default behaviour, which is to call showUriOnWindow.

Since: 2.18

afterLabelActivateLink :: (IsLabel a, MonadIO m) => a -> LabelActivateLinkCallback -> m SignalHandlerId

Connect a signal handler for the “activate-link” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after label #activateLink callback

genClosure_LabelActivateLink :: LabelActivateLinkCallback -> IO Closure

Wrap the callback into a Closure.

mk_LabelActivateLinkCallback :: C_LabelActivateLinkCallback -> IO (FunPtr C_LabelActivateLinkCallback)

Generate a function pointer callable from C code, from a C_LabelActivateLinkCallback.

noLabelActivateLinkCallback :: Maybe LabelActivateLinkCallback

A convenience synonym for Nothing :: Maybe LabelActivateLinkCallback.

onLabelActivateLink :: (IsLabel a, MonadIO m) => a -> LabelActivateLinkCallback -> m SignalHandlerId

Connect a signal handler for the “activate-link” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on label #activateLink callback

wrap_LabelActivateLinkCallback :: LabelActivateLinkCallback -> C_LabelActivateLinkCallback

Wrap a LabelActivateLinkCallback into a C_LabelActivateLinkCallback.

copyClipboard

type C_LabelCopyClipboardCallback = Ptr () -> Ptr () -> IO ()

Type for the callback on the (unwrapped) C side.

type LabelCopyClipboardCallback = IO ()

The ::copy-clipboard signal is a [keybinding signal][GtkBindingSignal] which gets emitted to copy the selection to the clipboard.

The default binding for this signal is Ctrl-c.

afterLabelCopyClipboard :: (IsLabel a, MonadIO m) => a -> LabelCopyClipboardCallback -> m SignalHandlerId

Connect a signal handler for the “copy-clipboard” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after label #copyClipboard callback

genClosure_LabelCopyClipboard :: LabelCopyClipboardCallback -> IO Closure

Wrap the callback into a Closure.

mk_LabelCopyClipboardCallback :: C_LabelCopyClipboardCallback -> IO (FunPtr C_LabelCopyClipboardCallback)

Generate a function pointer callable from C code, from a C_LabelCopyClipboardCallback.

noLabelCopyClipboardCallback :: Maybe LabelCopyClipboardCallback

A convenience synonym for Nothing :: Maybe LabelCopyClipboardCallback.

onLabelCopyClipboard :: (IsLabel a, MonadIO m) => a -> LabelCopyClipboardCallback -> m SignalHandlerId

Connect a signal handler for the “copy-clipboard” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on label #copyClipboard callback

wrap_LabelCopyClipboardCallback :: LabelCopyClipboardCallback -> C_LabelCopyClipboardCallback

Wrap a LabelCopyClipboardCallback into a C_LabelCopyClipboardCallback.

moveCursor

type C_LabelMoveCursorCallback = Ptr () -> CUInt -> Int32 -> CInt -> Ptr () -> IO ()

Type for the callback on the (unwrapped) C side.

type LabelMoveCursorCallback

Arguments

 = MovementStep

step: the granularity of the move, as a MovementStep

-> Int32

count: the number of step units to move

-> Bool

extendSelection: True if the move should extend the selection

-> IO ()

The ::move-cursor signal is a [keybinding signal][GtkBindingSignal] which gets emitted when the user initiates a cursor movement. If the cursor is not visible in entry, this signal causes the viewport to be moved instead.

Applications should not connect to it, but may emit it with g_signal_emit_by_name() if they need to control the cursor programmatically.

The default bindings for this signal come in two variants, the variant with the Shift modifier extends the selection, the variant without the Shift modifer does not. There are too many key combinations to list them all here.

• Arrow keys move by individual characters/lines
• Ctrl-arrow key combinations move by words/paragraphs
• Home/End keys move to the ends of the buffer

afterLabelMoveCursor :: (IsLabel a, MonadIO m) => a -> LabelMoveCursorCallback -> m SignalHandlerId

Connect a signal handler for the “move-cursor” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after label #moveCursor callback

genClosure_LabelMoveCursor :: LabelMoveCursorCallback -> IO Closure

Wrap the callback into a Closure.

mk_LabelMoveCursorCallback :: C_LabelMoveCursorCallback -> IO (FunPtr C_LabelMoveCursorCallback)

Generate a function pointer callable from C code, from a C_LabelMoveCursorCallback.

noLabelMoveCursorCallback :: Maybe LabelMoveCursorCallback

A convenience synonym for Nothing :: Maybe LabelMoveCursorCallback.

onLabelMoveCursor :: (IsLabel a, MonadIO m) => a -> LabelMoveCursorCallback -> m SignalHandlerId

Connect a signal handler for the “move-cursor” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on label #moveCursor callback

wrap_LabelMoveCursorCallback :: LabelMoveCursorCallback -> C_LabelMoveCursorCallback

Wrap a LabelMoveCursorCallback into a C_LabelMoveCursorCallback.

populatePopup

type C_LabelPopulatePopupCallback = Ptr () -> Ptr Menu -> Ptr () -> IO ()

Type for the callback on the (unwrapped) C side.

type LabelPopulatePopupCallback

Arguments

 = Menu

menu: the menu that is being populated

-> IO ()

The ::populate-popup signal gets emitted before showing the context menu of the label. Note that only selectable labels have context menus.

If you need to add items to the context menu, connect to this signal and append your menuitems to the menu.

afterLabelPopulatePopup :: (IsLabel a, MonadIO m) => a -> LabelPopulatePopupCallback -> m SignalHandlerId

Connect a signal handler for the “populate-popup” signal, to be run after the default handler. When overloading is enabled, this is equivalent to

after label #populatePopup callback

genClosure_LabelPopulatePopup :: LabelPopulatePopupCallback -> IO Closure

Wrap the callback into a Closure.

mk_LabelPopulatePopupCallback :: C_LabelPopulatePopupCallback -> IO (FunPtr C_LabelPopulatePopupCallback)

Generate a function pointer callable from C code, from a C_LabelPopulatePopupCallback.

noLabelPopulatePopupCallback :: Maybe LabelPopulatePopupCallback

A convenience synonym for Nothing :: Maybe LabelPopulatePopupCallback.

onLabelPopulatePopup :: (IsLabel a, MonadIO m) => a -> LabelPopulatePopupCallback -> m SignalHandlerId

Connect a signal handler for the “populate-popup” signal, to be run before the default handler. When overloading is enabled, this is equivalent to

on label #populatePopup callback

wrap_LabelPopulatePopupCallback :: LabelPopulatePopupCallback -> C_LabelPopulatePopupCallback

Wrap a LabelPopulatePopupCallback into a C_LabelPopulatePopupCallback.