<!-- ##### SECTION Title ##### -->GtkTreeSortable<!-- ##### SECTION Short_Description ##### -->The interface for sortable models used by GtkTreeView<!-- ##### SECTION Long_Description ##### --><para>#GtkTreeSortable is an interface to be implemented by tree models whichsupport sorting. The #GtkTreeView uses the methods provided by this interfaceto sort the model.</para><!-- ##### SECTION See_Also ##### --><para>#GtkTreeModel, #GtkTreeView</para><!-- ##### SECTION Stability_Level ##### --><!-- ##### STRUCT GtkTreeSortable ##### --><para></para><!-- ##### SIGNAL GtkTreeSortable::sort-column-changed ##### --><para></para>@treesortable: the object which received the signal.<!-- ##### STRUCT GtkTreeSortableIface ##### --><para></para>@g_iface: @sort_column_changed: @get_sort_column_id: @set_sort_column_id: @set_sort_func: @set_default_sort_func: @has_default_sort_func: <!-- ##### USER_FUNCTION GtkTreeIterCompareFunc ##### --><para>A GtkTreeIterCompareFunc should return a negative integer, zero, or a positiveinteger if @a sorts before @b, @a sorts with @b, or @a sorts after @brespectively. If two iters compare as equal, their order in the sorted model is undefined. In order to ensure that the #GtkTreeSortable behaves as expected, the GtkTreeIterCompareFunc must define a partial order on the model, i.e. it must be reflexive, antisymmetric and transitive.</para><para>For example, if @model is a product catalogue, then a compare functionfor the "price" column could be one which returns <literal>price_of(@a) - price_of(@b)</literal>.</para>@model: The #GtkTreeModel the comparison is within@a: A #GtkTreeIter in @model@b: Another #GtkTreeIter in @model@user_data: Data passed when the compare func is assigned e.g. bygtk_tree_sortable_set_sort_func()@Returns: <!-- ##### FUNCTION gtk_tree_sortable_sort_column_changed ##### --><para></para>@sortable: <!-- ##### FUNCTION gtk_tree_sortable_get_sort_column_id ##### --><para></para>@sortable: @sort_column_id: @order: @Returns: <!-- ##### FUNCTION gtk_tree_sortable_set_sort_column_id ##### --><para></para>@sortable: @sort_column_id: @order: <!-- ##### FUNCTION gtk_tree_sortable_set_sort_func ##### --><para></para>@sortable: @sort_column_id: @sort_func: @user_data: @destroy: <!-- ##### FUNCTION gtk_tree_sortable_set_default_sort_func ##### --><para></para>@sortable: @sort_func: @user_data: @destroy: <!-- ##### FUNCTION gtk_tree_sortable_has_default_sort_func ##### --><para></para>@sortable: @Returns: