一个官方的Overlay例子， overlay在很多情况下还是有很多用处的。
关键的几个地方
1. 创建OverlayEntry
OverlayEntry? overlayEntry;
overlayEntry = OverlayEntry(
// Create a new OverlayEntry.
builder: (BuildContext context) {
...
2. 使用insert方法把OverlayEntry插入到Overlay中
Overlay.of(context, debugRequiredFor: widget).insert(overlayEntry!);
3. 隐藏或者关闭时候删掉
overlayEntry?.remove();
完整代码如下
import 'package:flutter/material.dart';
/// Flutter code sample for [Overlay].
void main() => runApp(const OverlayApp());
class OverlayApp extends StatelessWidget {
const OverlayApp({super.key});
@override
Widget build(BuildContext context) {
return const MaterialApp(
home: OverlayExample(),
);
}
}
class OverlayExample extends StatefulWidget {
const OverlayExample({super.key});
@override
State<OverlayExample> createState() => _OverlayExampleState();
}
class _OverlayExampleState extends State<OverlayExample> {
OverlayEntry? overlayEntry;
int currentPageIndex = 0;
void createHighlightOverlay({
required AlignmentDirectional alignment,
required Color borderColor,
}) {
// Remove the existing OverlayEntry.
removeHighlightOverlay();
assert(overlayEntry == null);
overlayEntry = OverlayEntry(
// Create a new OverlayEntry.
builder: (BuildContext context) {
// Align is used to position the highlight overlay
// relative to the NavigationBar destination.
return SafeArea(
child: Align(
alignment: alignment,
heightFactor: 1.0,
child: DefaultTextStyle(
style: const TextStyle(
color: Colors.blue,
fontWeight: FontWeight.bold,
fontSize: 14.0,
),
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
const Text('Tap here for'),
Builder(builder: (BuildContext context) {
switch (currentPageIndex) {
case 0:
return const Column(
children: <Widget>[
Text(
'Explore page 1',
style: TextStyle(
color: Colors.red,
),
),
Icon(
Icons.arrow_downward,
color: Colors.red,
),
],
);
case 1:
return const Column(
children: <Widget>[
Text(
'Commute page 1',
style: TextStyle(
color: Colors.green,
),
),
Icon(
Icons.arrow_downward,
color: Colors.green,
),
],
);
case 2:
return const Column(
children: <Widget>[
Text(
'Saved page 1',
style: TextStyle(
color: Colors.orange,
),
),
Icon(
Icons.arrow_downward,
color: Colors.orange,
),
],
);
default:
return const Text('No page selected.');
}
}),
SizedBox(
width: MediaQuery.of(context).size.width / 3,
height: 80.0,
child: Center(
child: Container(
decoration: BoxDecoration(
border: Border.all(
color: borderColor,
width: 4.0,
),
),
),
),
),
],
),
),
),
);
},
);
// Add the OverlayEntry to the Overlay.
Overlay.of(context, debugRequiredFor: widget).insert(overlayEntry!);
}
// Remove the OverlayEntry.
void removeHighlightOverlay() {
overlayEntry?.remove();
overlayEntry = null;
}
@override
void dispose() {
// Make sure to remove OverlayEntry when the widget is disposed.
removeHighlightOverlay();
super.dispose();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Overlay Sample'),
),
bottomNavigationBar: NavigationBar(
selectedIndex: currentPageIndex,
destinations: const <NavigationDestination>[
NavigationDestination(
icon: Icon(Icons.explore),
label: 'Explore',
),
NavigationDestination(
icon: Icon(Icons.commute),
label: 'Commute',
),
NavigationDestination(
selectedIcon: Icon(Icons.bookmark),
icon: Icon(Icons.bookmark_border),
label: 'Saved',
),
],
),
body: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Text(
'Use Overlay to highlight a NavigationBar destination',
style: Theme.of(context).textTheme.bodyMedium,
),
const SizedBox(height: 20.0),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
// This creates a highlight Overlay for
// the Explore item.
ElevatedButton(
onPressed: () {
setState(() {
currentPageIndex = 0;
});
createHighlightOverlay(
alignment: AlignmentDirectional.bottomStart,
borderColor: Colors.red,
);
},
child: const Text('Explore'),
),
const SizedBox(width: 20.0),
// This creates a highlight Overlay for
// the Commute item.
ElevatedButton(
onPressed: () {
setState(() {
currentPageIndex = 1;
});
createHighlightOverlay(
alignment: AlignmentDirectional.bottomCenter,
borderColor: Colors.green,
);
},
child: const Text('Commute'),
),
const SizedBox(width: 20.0),
// This creates a highlight Overlay for
// the Saved item.
ElevatedButton(
onPressed: () {
setState(() {
currentPageIndex = 2;
});
createHighlightOverlay(
alignment: AlignmentDirectional.bottomEnd,
borderColor: Colors.orange,
);
},
child: const Text('Saved'),
),
],
),
const SizedBox(height: 10.0),
ElevatedButton(
onPressed: () {
removeHighlightOverlay();
},
child: const Text('Remove Overlay'),
),
],
),
);
}
}
