14 KiB
STRUCT
Label
The GtkLabel widget displays a small amount of text.
As the name implies, most labels are used to label another widget such as a [class@Button].
CSS nodes
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 GtkShortcutsWindow, labels are used with 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. In this case, label node also gets a .link style class.
GtkLabel as GtkBuildable
The GtkLabel implementation of the GtkBuildable interface supports a
custom <attributes> element, which supports any number of <attribute>
elements. The element has attributes named “name“, “value“,
“start“ and “end“ and allows you to specify [struct@Pango.Attribute]
values for this label.
An example of a UI definition fragment specifying Pango attributes:
<object class="GtkLabel"><attributes><attribute name="weight" value="PANGO_WEIGHT_BOLD"/><attribute 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.
Accessibility
GtkLabel uses the %GTK_ACCESSIBLE_ROLE_LABEL role.
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 [ctor@Gtk.Label.new_with_mnemonic] or
[method@Gtk.Label.set_text_with_mnemonic].
Mnemonics automatically activate any activatable widget the label is inside, such as a [class@Gtk.Button]; if the label is not inside the mnemonic’s target widget, you have to tell the label about the target using [class@Gtk.Label.set_mnemonic_widget]. Here’s a simple example where the label is inside a button:
// Pressing Alt+H will activate this button
GtkWidget *button = gtk_button_new ();
GtkWidget *label = gtk_label_new_with_mnemonic ("_Hello");
gtk_button_set_child (GTK_BUTTON (button), label);
There’s a convenience function to create buttons with a mnemonic label already inside:
// 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 [class@Gtk.Entry], you have to point the label at the entry with [method@Gtk.Label.set_mnemonic_widget]:
// 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:
Here’s how to create a label with a small font:
GtkWidget *label = gtk_label_new (NULL);
gtk_label_set_markup (GTK_LABEL (label), "<small>Small text</small>");
(See the Pango manual for complete documentation] of available tags, [func@Pango.parse_markup])
The markup passed to [method@Gtk.Label.set_markup] must be valid; for example,
literal <, > and & characters must be escaped as <, >, and &.
If you pass text obtained from the user, file, or a network to
[method@Gtk.Label.set_markup], you’ll want to escape it with
[func@GLib.markup_escape_text] or [func@GLib.markup_printf_escaped].
Markup strings are just a convenient way to set the [struct@Pango.AttrList] on a label; [method@Gtk.Label.set_attributes] may be a simpler way to set attributes in some cases. Be careful though; [struct@Pango.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 [struct@Pango.Attribute] requires knowledge of the exact string being displayed, so translations will cause problems.
Selectable labels
Labels can be made selectable with [method@Gtk.Label.set_selectable]. 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.
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 [method@Gtk.Label.set_wrap].
[method@Gtk.Label.set_justify] 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 [property@Gtk.Widget:halign] and [property@Gtk.Widget:valign] properties.
The [property@Gtk.Label:width-chars] and [property@Gtk.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.
Links
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“, “title“ and “class“ 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. The “class“ attribute is
used as style class on the CSS node for the link.
An example looks like this:
const char *text =
"Go to the "
"<a href=\"https://www.gtk.org\" title=\"<i>Our</i> 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 [signal@Gtk.Label::activate-link] signal and the [method@Gtk.Label.get_current_uri] function.
Properties
updateFunctions
Additional update functions for type extensions.
appearFunctions
Additional appear functions for type extensions.
accessibleRole
The accessible role of the given GtkAccessible implementation.
The accessible role cannot be changed once set.
label
The contents of the label.
If the string contains Pango markup (see [func@Pango.parse_markup]), you will have to set the [property@Gtk.Label:use-markup] property to %TRUE in order for the label to display the markup attributes. See also [method@Gtk.Label.set_markup] for a convenience function that sets both this property and the [property@Gtk.Label:use-markup] property at the same time.
If the string contains underlines acting as mnemonics, you will have to set the [property@Gtk.Label:use-underline] property to %TRUE in order for the label to display them.
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.
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 for details of how [property@Gtk.Label:width-chars] and [property@Gtk.Label:max-width-chars] determine the width of ellipsized and wrapped labels.
mnemonicKeyval
The mnemonic accelerator key for the label.
mnemonicWidget
The widget to be activated when the labels mnemonic key is pressed.
selectable
Whether the label text can be selected with the mouse.
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.
useMarkup
%TRUE if the text of the label includes Pango markup.
See [func@Pango.parse_markup].
useUnderline
%TRUE if the text of the label indicates a mnemonic with an _ before the mnemonic character.
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 for details of how [property@Gtk.Label:width-chars] and [property@Gtk.Label:max-width-chars] determine the width of ellipsized and wrapped labels.
wrap
%TRUE if the label text will wrap if it gets too wide.
xalign
The horizontal alignment of the label text inside its size allocation.
Compare this to [property@Gtk.Widget:halign], which determines how the labels size allocation is positioned in the space available for the label.
yalign
The vertical alignment of the label text inside its size allocation.
Compare this to [property@Gtk.Widget:valign], which determines how the labels size allocation is positioned in the space available for the label.
copyClipboard
Gets emitted to copy the selection to the clipboard.
The ::copy-clipboard signal is a keybinding signal.
The default binding for this signal is Ctrl+c.
app
The application.
window
The window.
Methods
init(label:)
Initialize Label.
container(modifiers:)
Get the widget's view storage.
- Parameter modifiers: The view modifiers.
- Returns: The view storage.
update(_:modifiers:updateProperties:)
Update the widget's view storage.
- Parameters:
- storage: The view storage.
- modifiers: The view modifiers.
- updateProperties: Whether to update the view's properties.
accessibleRole(_:)
The accessible role of the given GtkAccessible implementation.
The accessible role cannot be changed once set.
label(_:)
The contents of the label.
If the string contains Pango markup (see [func@Pango.parse_markup]), you will have to set the [property@Gtk.Label:use-markup] property to %TRUE in order for the label to display the markup attributes. See also [method@Gtk.Label.set_markup] for a convenience function that sets both this property and the [property@Gtk.Label:use-markup] property at the same time.
If the string contains underlines acting as mnemonics, you will have to set the [property@Gtk.Label:use-underline] property to %TRUE in order for the label to display them.
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.
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 for details of how [property@Gtk.Label:width-chars] and [property@Gtk.Label:max-width-chars] determine the width of ellipsized and wrapped labels.
mnemonicKeyval(_:)
The mnemonic accelerator key for the label.
mnemonicWidget(_:)
The widget to be activated when the labels mnemonic key is pressed.
selectable(_:)
Whether the label text can be selected with the mouse.
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.
useMarkup(_:)
%TRUE if the text of the label includes Pango markup.
See [func@Pango.parse_markup].
useUnderline(_:)
%TRUE if the text of the label indicates a mnemonic with an _ before the mnemonic character.
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 for details of how [property@Gtk.Label:width-chars] and [property@Gtk.Label:max-width-chars] determine the width of ellipsized and wrapped labels.
wrap(_:)
%TRUE if the label text will wrap if it gets too wide.
xalign(_:)
The horizontal alignment of the label text inside its size allocation.
Compare this to [property@Gtk.Widget:halign], which determines how the labels size allocation is positioned in the space available for the label.
yalign(_:)
The vertical alignment of the label text inside its size allocation.
Compare this to [property@Gtk.Widget:valign], which determines how the labels size allocation is positioned in the space available for the label.
copyClipboard(_:)
Gets emitted to copy the selection to the clipboard.
The ::copy-clipboard signal is a keybinding signal.
The default binding for this signal is Ctrl+c.