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gesture the user intends by having each recognizer join
the gesture arena. the gesture arena determines which
gesture wins using the following rules:
at any time, a recognizer can eliminate itself and leave the
arena. if there’s only one recognizer left in the arena,
that recognizer wins.
at any time, a recognizer can declare itself the winner,
causing all of the remaining recognizers to lose.
for example, when disambiguating horizontal and vertical dragging,
both recognizers enter the arena when they receive the pointer
down event. the recognizers observe the pointer move events.
if the user moves the pointer more than a certain number of
logical pixels horizontally, the horizontal recognizer declares
the win and the gesture is interpreted as a horizontal drag.
similarly, if the user moves more than a certain number of logical
pixels vertically, the vertical recognizer declares itself the winner.
the gesture arena is beneficial when there is only a horizontal
(or vertical) drag recognizer. in that case, there is only one
recognizer in the arena and the horizontal drag is recognized
immediately, which means the first pixel of horizontal movement
can be treated as a drag and the user won’t need to wait for
further gesture disambiguation.
<topic_end>
<topic_start>
handle taps
you not only want to display information to users,
you want users to interact with your app.
use the GestureDetector widget to respond
to fundamental actions, such as tapping and dragging.
info note
to learn more, watch this short widget of the week video on the GestureDetector widget:
this recipe shows how to make a custom button that shows
a snackbar when tapped with the following steps:
<code_start>
// the GestureDetector wraps the button.
GestureDetector(
// when the child is tapped, show a snackbar.
onTap: () {
const snackBar = SnackBar(content: Text('Tap'));
ScaffoldMessenger.of(context).showSnackBar(snackBar);
},
// the custom button
child: container(
padding: const EdgeInsets.all(12),
decoration: BoxDecoration(
color: Colors.lightBlue,
borderRadius: BorderRadius.circular(8),
),
child: const Text('My button'),
),
)
<code_end>
<topic_end>
<topic_start>
notes
<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 title = 'gesture demo';
return const MaterialApp(
title: title,
home: MyHomePage(title: title),
);
}
}
class MyHomePage extends StatelessWidget {
final string title;
const MyHomePage({super.key, required this.title});
@override
widget build(BuildContext context) {
return scaffold(
appBar: AppBar(
title: text(title),
),
body: const center(
child: MyButton(),
),
);
}
}
class MyButton extends StatelessWidget {
const MyButton({super.key});
@override
widget build(BuildContext context) {
// the GestureDetector wraps the button.
return GestureDetector(
// when the child is tapped, show a snackbar.
onTap: () {
const snackBar = SnackBar(content: Text('Tap'));
ScaffoldMessenger.of(context).showSnackBar(snackBar);
},
// the custom button
child: container(