Appbar hide by Overlay in flutter

Question

In my Page I have 12 Textformfields. These 12 textformfields are inside the SingleChildScrollView. When I scroll the page, the overlays and the focusnodes are come to the top of the Appbar.

class _SampleState extends State<Sample> {
  var scaffoldkey=GlobalKey<ScaffoldState>();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
    appBar:AppBar(title: Text('fvbnm'),backgroundColor: Colors.red,),
    body:SingleChildScrollView(child: Column(children: [Table(children: [
    TableRow(children: [Column(children: [Text('Name')],),Column(children: [TextFormField(decoration:InputDecoration())],)]),
      TableRow(children: [Column(children: [Text('Name')],),Column(children: [TextFormField(decoration:InputDecoration())],)]),
    ])],),));}}