PageView and GestureDetector bug

[Vítor Magalhães]

Hi,

I've been struggling with some weird edge case in the use of GestureDetector inside of PageView children. Basically, the GestureDetectors work correctly with the exception when the PageView only has two children. In this case, when index 0 is centered the gesture detector on index 1 never fires when tapping on it. If I add a new child then index 1 is tappable.

This is a sample code that replicates the issue, any feedback is welcome. Thanks

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

// This widget is the root of your application.

@override

Widget build(BuildContext context) {

return MaterialApp(

title: 'Flutter Demo',

theme: ThemeData(

// This is the theme of your application.

//

// Try running your application with "flutter run". You'll see the

// application has a blue toolbar. Then, without quitting the app, try

// changing the primarySwatch below to Colors.green and then invoke

// "hot reload" (press "r" in the console where you ran "flutter run",

// or simply save your changes to "hot reload" in a Flutter IDE).

// Notice that the counter didn't reset back to zero; the application

// is not restarted.

primarySwatch: Colors.blue,

),

home: MyHomePage(title: 'Flutter Demo Home Page'),

);

}

}

class MyHomePage extends StatefulWidget {

MyHomePage({Key key, this.title}) : super(key: key);

// This widget is the home page of your application. It is stateful, meaning

// that it has a State object (defined below) that contains fields that affect

// how it looks.

// This class is the configuration for the state. It holds the values (in this

// case the title) provided by the parent (in this case the App widget) and

// used by the build method of the State. Fields in a Widget subclass are

// always marked "final".

final String title;

@override

_MyHomePageState createState() => _MyHomePageState();

}

class _MyHomePageState extends State<MyHomePage> {

int _counter = 0;

final _pageController = PageController(viewportFraction: 0.8);

void _incrementCounter() {

setState(() {

// This call to setState tells the Flutter framework that something has

// changed in this State, which causes it to rerun the build method below

// so that the display can reflect the updated values. If we changed

// _counter without calling setState(), then the build method would not be

// called again, and so nothing would appear to happen.

_counter++;

});

}

@override

Widget build(BuildContext context) {

// This method is rerun every time setState is called, for instance as done

// by the _incrementCounter method above.

//

// The Flutter framework has been optimized to make rerunning build methods

// fast, so that you can just rebuild anything that needs updating rather

// than having to individually change instances of widgets.

return Scaffold(

appBar: AppBar(

// Here we take the value from the MyHomePage object that was created by

// the App.build method, and use it to set our appbar title.

title: Text(widget.title),

),

body: PageView(

controller: _pageController,

children: <Widget>[

GestureDetector(

onTap: () => print('tap 0'),

child: Container(

alignment: Alignment.center,

color: Colors.blue,

child: Text('0')),

),

GestureDetector(

onTap: () => print('tap 1'),

child: Container(

alignment: Alignment.center,

color: Colors.red,

child: Text('1')),

),

],

),

floatingActionButton: FloatingActionButton(

onPressed: _incrementCounter,

tooltip: 'Increment',

child: Icon(Icons.add),

), // This trailing comma makes auto-formatting nicer for build methods.

);

}

}