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setState(() {
_visible = !_visible;
});
},
tooltip: 'toggle opacity',
child: const Icon(Icons.flip),
)
<code_end>
<topic_end>
<topic_start>
4. fade the box in and out
you have a green box on screen and a button to toggle the visibility
to true or false. how to fade the box in and out? with an
AnimatedOpacity widget.
the AnimatedOpacity widget requires three arguments:
<code_start>
AnimatedOpacity(
// if the widget is visible, animate to 0.0 (invisible).
// if the widget is hidden, animate to 1.0 (fully visible).
opacity: _visible ? 1.0 : 0.0,
duration: const duration(milliseconds: 500),
// the green box must be a child of the AnimatedOpacity widget.
child: container(
width: 200,
height: 200,
color: colors.green,
),
)
<code_end>
<topic_end>
<topic_start>
interactive example
<code_start>
import 'package:flutter/material.dart';
void main() => runApp(const MyApp());
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
widget build(BuildContext context) {
const appTitle = 'opacity demo';
return const MaterialApp(
title: appTitle,
home: MyHomePage(title: appTitle),
);
}
}
// the StatefulWidget's job is to take data and create a state class.
// in this case, the widget takes a title, and creates a _MyHomePageState.
class MyHomePage extends StatefulWidget {
const MyHomePage({
super.key,
required this.title,
});
final string title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
// the state class is responsible for two things: holding some data you can
// update and building the UI using that data.
class _MyHomePageState extends State<MyHomePage> {
// whether the green box should be visible
bool _visible = true;
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(
title: text(widget.title),
),
body: center(
child: AnimatedOpacity(
// if the widget is visible, animate to 0.0 (invisible).
// if the widget is hidden, animate to 1.0 (fully visible).
opacity: _visible ? 1.0 : 0.0,
duration: const duration(milliseconds: 500),
// the green box must be a child of the AnimatedOpacity widget.
child: container(
width: 200,
height: 200,
color: colors.green,
),
),
),
floatingActionButton: FloatingActionButton(
onPressed: () {
// call setState. this tells flutter to rebuild the
// UI with the changes.
setState(() {
_visible = !_visible;
});
},
tooltip: 'toggle opacity',
child: const Icon(Icons.flip),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
hero animations