addFromString
Parses a string containing a UI definition and merges it with the current contents of @builder.
This function is useful if you need to call method@Gtk.Builder.set_current_object to add user data to callbacks before loading GtkBuilder UI. Otherwise, you probably want ctor@Gtk.Builder.new_from_string instead.
Upon errors false will be returned and @error will be assigned a GError from the %GTK_BUILDER_ERROR, %G_MARKUP_ERROR or %G_VARIANT_PARSE_ERROR domain.
It’s not really reasonable to attempt to handle failures of this call. The only reasonable thing to do when an error is detected is to call g_error().
Return
true on success, false if an error occurred
Parameters
buffer
the string to parse
length
the length of @buffer (may be -1 if @buffer is nul-terminated)