Gtk.Widget::drag-begin

function callback(widget, context:Gdk.DragContext, ):void;

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. Gtk.Widget.prototype.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 g_signal_connect_after() to override what the default handler did.