public virtual signal void drag_begin (DragContext context)
The drag_begin signal is emitted on the drag source when a drag is started.
A typical reason to connect to this signal is to set up a custom drag icon with e.g. drag_source_set_icon_pixbuf.
Note that some widgets set up a drag icon in the default handler of this signal, so you may have to use connect_after to override what the default handler did.
the drag context