PopupMenuButton

// This is the type used by the popup menu below.
enum WhyFarther { harder, smarter, selfStarter, tradingCharter }

// This menu button widget updates a _selection field (of type WhyFarther,
// not shown here).
PopupMenuButton<WhyFarther>(
  onSelected: (WhyFarther result) { setState(() { _selection = result; }); },
  itemBuilder: (BuildContext context) => <PopupMenuEntry<WhyFarther>>[
    const PopupMenuItem<WhyFarther>(
      value: WhyFarther.harder,
      child: Text('Working a lot harder'),
    ),
    const PopupMenuItem<WhyFarther>(
      value: WhyFarther.smarter,
      child: Text('Being a lot smarter'),
    ),
    const PopupMenuItem<WhyFarther>(
      value: WhyFarther.selfStarter,
      child: Text('Being a self-starter'),
    ),
    const PopupMenuItem<WhyFarther>(
      value: WhyFarther.tradingCharter,
      child: Text('Placed in charge of trading charter'),
    ),
  ],
)