By setting a header function on the @box one can dynamically add headers
in front of rows, depending on the contents of the row and its position
in the list.
For instance, one could use it to add headers in front of the first item
of a new kind, in a list sorted by the kind.
The @update_header can look at the current header widget using
[method@Gtk.ListBoxRow.get_header] and either update the state of the widget
as needed, or set a new one using [method@Gtk.ListBoxRow.set_header]. If no
header is needed, set the header to %NULL.
Note that you may get many calls @update_header to this for a particular
row when e.g. changing things that don’t affect the header. In this case
it is important for performance to not blindly replace an existing header
with an identical one.
The @update_header function will be called for each row after the call,
and it will continue to be called each time a row changes (via
[method@Gtk.ListBoxRow.changed]) and when the row before changes (either
by [method@Gtk.ListBoxRow.changed] on the previous row, or when the previous
row becomes a different row). It is also called for all rows when
[method@Gtk.ListBox.invalidate_headers] is called.
Sets a header function.
By setting a header function on the @box one can dynamically add headers in front of rows, depending on the contents of the row and its position in the list.
For instance, one could use it to add headers in front of the first item of a new kind, in a list sorted by the kind.
The @update_header can look at the current header widget using [method@Gtk.ListBoxRow.get_header] and either update the state of the widget as needed, or set a new one using [method@Gtk.ListBoxRow.set_header]. If no header is needed, set the header to %NULL.
Note that you may get many calls @update_header to this for a particular row when e.g. changing things that don’t affect the header. In this case it is important for performance to not blindly replace an existing header with an identical one.
The @update_header function will be called for each row after the call, and it will continue to be called each time a row changes (via [method@Gtk.ListBoxRow.changed]) and when the row before changes (either by [method@Gtk.ListBoxRow.changed] on the previous row, or when the previous row becomes a different row). It is also called for all rows when [method@Gtk.ListBox.invalidate_headers] is called.