GtkLabel implements
AtkImplementorIface and GtkBuildable.
Detailed Description
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.
GtkLabel as GtkBuildable
The GtkLabel implementation of the GtkBuildable interface supports a
custom element, which supports any number of
elements. the element has attributes named name, value,
start and end and allows you to specify PangoAttribute values for this label.
A UI definition fragment specifying Pango attributes
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 gtkLabelNewWithMnemonic or
gtkLabelSetTextWithMnemonic.
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 gtkLabelSetMnemonicWidget. Here's a simple example where
the label is inside a button:
## Pressing Alt-H will activate this button
button <- gtkButton()
label <- gtkLabelNewWithMnemonic("_Hello")
button$add(label)
There's a convenience function to create buttons with a mnemonic label
already inside:
## Pressing Alt+H will activate this button
button <- gtkButtonNewWithMnemonic("_Hello")
To create a mnemonic for a widget alongside the label, such as a
GtkEntry, you have to point the label at the entry with
gtkLabelSetMnemonicWidget:
## Pressing Alt+H will focus the entry
entry <- gtkEntry()
label <- gtkLabelNewWithMnemonic("_Hello")
label$setMnemonicWidget(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:
label <- gtkLabelNew()
label$setMarkup("Small text")
(See complete documentation of available
tags in the Pango manual.)
The markup passed to gtkLabelSetMarkup 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 gtkLabelSetMarkup, you'll want to escape it with
gMarkupEscapeText() or gMarkupPrintfEscaped().
Markup strings are just a convenient way to set the PangoAttrList on
a label; gtkLabelSetAttributes 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.
Selectable labels
Labels can be made selectable with gtkLabelSetSelectable.
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
gtkLabelSetLineWrap.
gtkLabelSetJustify 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 gtkMiscSetAlignment.
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:
label$setMarkup("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 gtkLabelGetCurrentUri function.
Convenient Construction
gtkLabel is the result of collapsing the constructors of GtkLabel (gtkLabelNew, gtkLabelNewWithMnemonic) and accepts a subset of its arguments matching the required arguments of one of its delegate constructors.