Sets a user function for determining where a column may be dropped when
dragged. This function is called on every column pair in turn at the
beginning of a column drag to determine where a drop can take place. The
arguments passed to func are: the tree_view, the gtk.TreeViewColumn being
dragged, the two gtk.TreeViewColumn s determining the drop spot, and
user_data. If either of the gtk.TreeViewColumn arguments for the drop spot
are NULL, then they indicate an edge. If func is set to be NULL, then
tree_view reverts to the default behavior of allowing all columns to be
dropped everywhere.
Sets a user function for determining where a column may be dropped when dragged. This function is called on every column pair in turn at the beginning of a column drag to determine where a drop can take place. The arguments passed to func are: the tree_view, the gtk.TreeViewColumn being dragged, the two gtk.TreeViewColumn s determining the drop spot, and user_data. If either of the gtk.TreeViewColumn arguments for the drop spot are NULL, then they indicate an edge. If func is set to be NULL, then tree_view reverts to the default behavior of allowing all columns to be dropped everywhere.