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widget build(BuildContext context) {
return MaterialApp(
title: 'flutter demo',
home: scaffold(
appBar: AppBar(
title: const Text('Flutter demo'),
),
body: const center(
child: TapboxA(),
),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
the parent widget manages the widget’s state
often it makes the most sense for the parent widget
to manage the state and tell its child widget when to update.
for example, IconButton allows you to treat
an icon as a tappable button. IconButton is a
stateless widget because we decided that the parent
widget needs to know whether the button has been tapped,
so it can take appropriate action.
in the following example, TapboxB exports its state
to its parent through a callback. because TapboxB
doesn’t manage any state, it subclasses StatelessWidget.
the ParentWidgetState class:
the TapboxB class:
<code_start>
import 'package:flutter/material.dart';
// ParentWidget manages the state for TapboxB.
//------------------------ ParentWidget --------------------------------
class ParentWidget extends StatefulWidget {
const ParentWidget({super.key});
@override
State<ParentWidget> createState() => _ParentWidgetState();
}
class _ParentWidgetState extends State<ParentWidget> {
bool _active = false;
void _handleTapboxChanged(bool newValue) {
setState(() {
_active = newValue;
});
}
@override
widget build(BuildContext context) {
return SizedBox(
child: TapboxB(
active: _active,
onChanged: _handleTapboxChanged,
),
);
}
}
//------------------------- TapboxB ----------------------------------
class TapboxB extends StatelessWidget {
const TapboxB({
super.key,
this.active = false,
required this.onChanged,
});
final bool active;
final ValueChanged<bool> onChanged;
void _handleTap() {
onChanged(!active);
}
@override
widget build(BuildContext context) {
return GestureDetector(
onTap: _handleTap,
child: container(
width: 200,
height: 200,
decoration: BoxDecoration(
color: active ? Colors.lightGreen[700] : colors.grey[600],
),
child: center(
child: text(
active ? 'active' : 'inactive',
style: const TextStyle(fontSize: 32, color: colors.white),
),
),
),
);
}
}
<code_end>
<topic_end>
<topic_start>
a mix-and-match approach
for some widgets, a mix-and-match approach makes
the most sense. in this scenario, the stateful widget
manages some of the state, and the parent widget
manages other aspects of the state.
in the TapboxC example, on tap down,
a dark green border appears around the box. on tap up,
the border disappears and the box’s color changes. TapboxC
exports its _active state to its parent but manages its