How to display active textfields hidden by the front panel? - user-interface

Question

I have been trying to display backdrop with searching fiture. but when I tap the textfield is hidden by front panel. how to front panel not hidden the search textfield ?
import 'package:flutter/material.dart';
import 'content_isi.dart';
class Panel extends StatefulWidget {
final AnimationController controller;
Panel({this.controller});
#override
_PanelState createState() => new _PanelState();
}
class _PanelState extends State<Panel> {
static const header_height = 200.0;
Animation<RelativeRect> getPanelAnimation(BoxConstraints constraints) {
final height = constraints.biggest.height;
final backPanelHeight = height - header_height;
final frontPanelHeight = -header_height;
return new RelativeRectTween(
begin: new RelativeRect.fromLTRB(
0.0, backPanelHeight, 0.0, frontPanelHeight),
end: new RelativeRect.fromLTRB(0.0, 0.0, 0.0, 0.0))
.animate(new CurvedAnimation(
parent: widget.controller, curve: Curves.linear));
}
Widget bothPanels(BuildContext context, BoxConstraints constraints) {
final ThemeData theme = Theme.of(context);
return new Container(
child: new Stack(
children: <Widget>[
new Container(
color: Colors.white,
child: Column(
children: <Widget>[
TextField(
decoration:
_buildInputDecoration(Icons.tune, 'Jenis Peraturan'),
),
Divider(
height: 0.0,
color: Colors.grey,
),
TextField(
decoration: _buildInputDecoration(Icons.pages, 'Nomor'),
),
Divider(
height: 0.0,
color: Colors.grey,
),
TextField(
decoration: _buildInputDecoration(Icons.pages, 'Tahun'),
),
Divider(
height: 0.0,
color: Colors.grey,
),
TextField(
decoration:
_buildInputDecoration(Icons.help_outline, 'Tentang'),
),
Container(
padding: EdgeInsets.only(left: 5.0, right: 5.0),
width: double.infinity,
child: FlatButton(
onPressed: () {},
child: Text(
'Cari',
style: TextStyle(
color: Colors.white,
fontWeight: FontWeight.bold,
fontSize: 16),
),
color: Colors.blue,
),
),
],
),
),
new PositionedTransition(
rect: getPanelAnimation(constraints),
child: new Material(
elevation: 12.0,
child: ListView(
children: <Widget>[
ContentIsi(
no: '11',
th: '2020',
jnsperaturan: 'Peraturan BBB',
judul:
'Perubahan Keempat Atas Peraturan Nomor 1 Tahun 2017 tentang Pelimpahan Kewenangan Penandatanganan Perizinan dan Non Perizinan Kepada Kepala Dinas Penanaman Modal dan Pelayanan Terpadu Satu Pintu',
onPressed: null,
)
],
),
),
)
],
),
);
}
#override
Widget build(BuildContext context) {
return new LayoutBuilder(
builder: bothPanels,
);
}
InputDecoration _buildInputDecoration(IconData icon, String hintText) {
return InputDecoration(
prefixIcon: Padding(
padding: const EdgeInsets.only(right: 32.0, left: 16.0),
child: Icon(icon),
),
hintText: hintText,
contentPadding: const EdgeInsets.symmetric(vertical: 16.0),
border: InputBorder.none,
);
}
}
I'm the beginner of flutter. so i hope you can help me about it.
the gif image in the below :
in the image gif the textfield hidden by front pannel (listview) when I tap the textfield. how to fix it ????