Returns true if the model has a default sort function. This is used primarily by
GtkTreeViewColumns in order to determine if a model can go back to the default state, or not.
Sets the default comparison function used when sorting to be sort_func. If the current
sort column id of sortable is DEFAULT, then the model will
sort using this function.
Sets the comparison function used when sorting to be sort_func. If the current sort
column id of sortable is the same as sort_column_id, then the model will sort using this function.
The sort_column_changed signal
is emitted when the sort column or sort order of sortable is changed. The signal is emitted before the contents of
sortable are resorted.