restrict back button
@override
Widget build(BuildContext context) {
return new WillPopScope(
onWillPop: () async => false,
child: new Scaffold(
appBar: new AppBar(
title: new Text("data"),
leading: new IconButton(
icon: new Icon(Icons.ac_unit),
onPressed: () => Navigator.of(context).pop(),
),
),
),
);
}