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The GtkLabel widget displays a small amount of text. As the name implies, most labels are used to label another widget such as a GtkButton, a GtkMenuItem, or a GtkOptionMenu.
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 PangoAttribute values for this label.
Example 7. A UI definition fragment specifying Pango attributes
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<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.
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 gtk_label_new_with_mnemonic()
or
gtk_label_set_text_with_mnemonic()
.
Mnemonics automatically activate any activatable widget the label is
inside, such as a GtkButton; if the label is not inside the
mnemonic's target widget, you have to tell the label about the target
using gtk_label_set_mnemonic_widget()
. Here's a simple example where
the label is inside a button:
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/* Pressing Alt+H will activate this button */ button = gtk_button_new (); 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:
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/* Pressing Alt+H will activate this button */ button = gtk_button_new_with_mnemonic ("_Hello"); |
To create a mnemonic for a widget alongside the label, such as a
GtkEntry, you have to point the label at the entry with
gtk_label_set_mnemonic_widget()
:
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/* Pressing Alt+H will focus the entry */ entry = gtk_entry_new (); label = gtk_label_new_with_mnemonic ("_Hello"); gtk_label_set_mnemonic_widget (GTK_LABEL (label), entry); |
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:
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label = gtk_label_new (NULL); gtk_label_set_markup (GTK_LABEL (label), "<small>Small text</small>"); |
(See complete documentation of available tags in the Pango manual.)
The markup passed to gtk_label_set_markup()
must be valid; for example,
literal </>/& characters must be escaped as <,
>, and &. If you pass text obtained from the user, file,
or a network to gtk_label_set_markup()
, you'll want to escape it with
g_markup_escape_text()
or g_markup_printf_escaped()
.
Markup strings are just a convenient way to set the PangoAttrList on
a label; gtk_label_set_attributes()
may be a simpler way to set
attributes in some cases. Be careful though; PangoAttrList 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 PangoAttribute requires knowledge of the exact string
being displayed, so translations will cause problems.
Labels can be made selectable with 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.
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
gtk_label_set_line_wrap()
.
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 gtk_misc_set_alignment()
.
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:
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gtk_label_set_markup (label, "Go to the <a href=\"http://www.gtk.org\" title=\"<i>Our</i> website\">GTK+ website</a> for more..."); |
It is possible to implement custom handling for links and their tooltips with
the “activate-link” signal and the gtk_label_get_current_uri()
function.