set_column_drag_function

Description:

public void set_column_drag_function (owned TreeViewColumnDropFunc? func)

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 this, the TreeViewColumn being dragged, the two TreeViewColumn s determining the drop spot, and user_data. If either of the TreeViewColumn arguments for the drop spot are null, then they indicate an edge. If func is set to be null, then this reverts to the default behavior of allowing all columns to be dropped everywhere.

Parameters:

this	A TreeView.
func	A function to determine which columns are reorderable, or null.
destroy	Destroy notifier for `user_data`, or null
user_data	User data to be passed to `func`, or null