Navigating from a plugin callback - flutter

Question

The problem is when I want to navigate from a callback - which is invoked by plugin - new page is pushed in as a widget inside my page.
This is the code:
import 'dart:async';
import 'package:barcode_scan/barcode_scan.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
void main() {
runApp(new MaterialApp(
home: new MyApp(),
) );
}
class MyApp extends StatefulWidget {
#override
_MyAppState createState() => new _MyAppState();
}
class _MyAppState extends State<MyApp> {
String barcode = "";
#override
initState() {
super.initState();
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(
title: new Text('Barcode Scanner Example'),
),
body: new Center(
child: new Column(
children: <Widget>[
new Container(
child: new MaterialButton(
onPressed: scan, child: new Text("Scan")),
padding: const EdgeInsets.all(8.0),
),
],
),
));
}
Future scan() async {
try {
String barcode = await BarcodeScanner.scan();
print("${context}");
Navigator.push(context, MaterialPageRoute(
builder: (context) {
return new BarcodePage(barcode);}
));
setState(() => this.barcode = barcode);
} on PlatformException catch (e) {
if (e.code == BarcodeScanner.CameraAccessDenied) {
setState(() {
this.barcode = 'The user did not grant the camera permission!';
});
} else {
setState(() => this.barcode = 'Unknown error: $e');
}
} on FormatException{
setState(() => this.barcode = 'null (User returned using the "back"-button before scanning anything. Result)');
} catch (e) {
setState(() => this.barcode = 'Unknown error: $e');
}
}
}
class BarcodePage extends StatefulWidget {
BarcodePage(String s) {
str = s;
}
String str;
#override
State<StatefulWidget> createState() {
return _BarcodePageState(str);
}
}
class _BarcodePageState extends State<BarcodePage> {
String str;
_BarcodePageState(String s ){
str = s;
}
#override
Widget build(BuildContext context) {
return new Scaffold(
appBar: new AppBar(title: new Text("Bar code"),),
body: new Text(str),
);
}
}
You can find the application in https://github.com/arashbi/flutter_barcode_reader example folder
This is related to my question before, but simpler setup.

Answer 1

AFAI understand the problem is that callback is happening in the middle of render pipeline, and it causes the wrong behaviour. The solution is to use either Future.delayed or SchedulerBinding.instance.addPostFrameCallback
These methods causes the navigation to happen after the render pipeline, and the navigator can do its job properly