Alert Dialog flutter error only valid value 0:1 - flutter

Question

I did a simple alert function
Github : https://github.com/mohammad092/first
void newAlert(BuildContext context) {
showDialog(
context: context,
builder: (BuildContext context){
return AlertDialog(
title: Text('title text'),
content: Text('content text'),
actions: [
FlatButton(
onPressed: (){
Navigator.of(context).pop();
},
child: Text('dismiss'),
),
],
);
},
);
}
and i import it to my main.dart
also i imported the file which has the alert function
body: RaisedButton(
child: Text('Alert'),
onPressed: () {
newAlert(context);
}),
...
when i press the button on my device its keeps saying:
======== Exception caught by gesture library ================
The following RangeError was thrown while routing a pointer event:
RangeError (index): Invalid value: Only valid value is 0: 1

Answer 1

You are getting the error because your main.dart is not implemented correctly.You're declaring your RaisedButton directly in the MyApp class, instead you should make another Widget and pass that to MyApp, that will give the correct context to show the alert.
Change your main.dart to this :
import 'package:flutter/material.dart';
import 'package:your_project/alert.dart';
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
visualDensity: VisualDensity.adaptivePlatformDensity,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
#override
Widget build(BuildContext context) {
return Scaffold(
body: Center(
child: RaisedButton(
child: Text('Alert'),
onPressed: () {
newAlert(context);
},
),
),
);
}
}

Answer 2

Use the below code
Future<void> _showMyDialog() async {
return showDialog<void>(
context: context,
barrierDismissible: false, // user must tap button!
builder: (BuildContext context) {
return AlertDialog(
title: Text('AlertDialog Title'),
content: SingleChildScrollView(
child: ListBody(
children: <Widget>[
Text('This is a demo alert dialog.'),
Text('Would you like to approve of this message?'),
],
),
),
actions: <Widget>[
TextButton(
child: Text('Approve'),
onPressed: () {
Navigator.of(context).pop();
},
),
],
);
},
);
}
body: RaisedButton(
child: Text('Alert'),
onPressed: () {
_showMyDialog()
}),
...