先看一下效果：
未展开图：
展开图：
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData(
primaryColor: Colors.red,
primarySwatch: Colors.teal,
),
home: BackDrop(),
);
}
}
class BackDrop extends StatefulWidget {
@override
_BackDropState createState() => _BackDropState();
}
class _BackDropState extends State<BackDrop>
with SingleTickerProviderStateMixin {
AnimationController animationController;
@override
void initState() {
super.initState();
animationController = AnimationController(
vsync: this,
duration: Duration(milliseconds: 100),
value: 1,
);
}
@override
void dispose() {
super.dispose();
animationController.dispose();
}
bool get isPanelVisible {
final AnimationStatus status = animationController.status;
return status == AnimationStatus.completed ||
status == AnimationStatus.forward;
}
Animation<RelativeRect> getPanelAnimation(BoxConstraints constraints) {
final height = constraints.biggest.height;
final backHeight = height - 32;
final frontHeight = -32.0;
return RelativeRectTween(
begin: RelativeRect.fromLTRB(0.0, backHeight, 0.0, frontHeight),
end: RelativeRect.fromLTRB(0.0, 60.0, 0.0, 0.0))
.animate(CurvedAnimation(
parent: animationController, curve: Curves.easeInOut));
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Backdrop'),
leading: IconButton(
onPressed: () {
animationController.fling(velocity: isPanelVisible ? -1.0 : 1.0);
},
icon: AnimatedIcon(
icon: AnimatedIcons.close_menu,
progress: animationController.view,
),
),
),
body: LayoutBuilder(
builder: (BuildContext context, BoxConstraints constraints) {
return Container(
child: Stack(
children: <Widget>[
Container(
color: Colors.blue,
child: Center(
child: Text(
'Back Panl',
style: TextStyle(color: Colors.white, fontSize: 28.0),
),
),
),
PositionedTransition(
rect: getPanelAnimation(constraints),
child: Material(
elevation: 4.0,
borderRadius: BorderRadius.only(
topLeft: Radius.circular(16.0),
topRight: Radius.circular(16.0),
),
child: Column(
children: <Widget>[
Container(
height: 32,
child: Text(
'Shop Here',
style: TextStyle(color: Colors.red),
),
),
Expanded(
child: Center(
child: Text('Front Panl',
style: TextStyle(
color: Colors.red, fontSize: 28.0)),
),
)
],
),
),
)
],
),
);
},
),
);
}
}
