Why is Navigator.pop failing to pass a parameter back? - flutter

Question

I'm launching an alert dialog to confirm a user's action of saving or clearing a filter, and I want to return a boolean based on their selection. I'm trying to pass it through Navigator.pop() but keep getting this error:
The following _TypeError was thrown while handling a gesture:
type 'bool' is not a subtype of type 'AlertDialog' of 'result'
Anyone know why this is happening? Here is my code. The specific error is happening in the onPressed where I assign the result of showDialog to a var shouldClear.
import 'package:flutter/material.dart';
class FilterNavbar extends StatelessWidget {
final VoidCallback clearFilter;
const FilterNavbar({#required this.clearFilter});
#override
Widget build(BuildContext context) {
return Container(
height: 60,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: MediaQuery.of(context).size.width * .3,
child: RaisedButton(
onPressed: () async {
var shouldClear = await showDialog<AlertDialog>(
context: context,
builder: (context) {
return generateDialog(context, attemptSave: false);
}
);
},
child: const Text("Clear"),
),
),
Container(
width: MediaQuery.of(context).size.width * .3,
child: RaisedButton(
onPressed: () async {
await showDialog<AlertDialog>(
context: context,
builder: (context) {
return generateDialog(context, attemptSave: true);
}
);
Navigator.pop(context, true);
},
child: const Text("Save"),
),
)
]
),
);
}
}
AlertDialog generateDialog(BuildContext context, {bool attemptSave}){
return AlertDialog(
title: Center(child: Text("${attemptSave ? "Save": "Clear"} filter?")),
actions: [
FlatButton(
onPressed: () {
if (attemptSave) {
Navigator.pop(context, false);
}
else {
Navigator.pop(context, true);
}
},
child: Text("${attemptSave ? "Save": "Clear"}")
)
],
);
}

Answer 1

You can copy paste run full code below
Please change AlertDialog to bool
From
await showDialog<AlertDialog>
to
await showDialog<bool>
working demo
full code
import 'package:flutter/material.dart';
class FilterNavbar extends StatelessWidget {
final VoidCallback clearFilter;
const FilterNavbar({#required this.clearFilter});
#override
Widget build(BuildContext context) {
return Container(
height: 60,
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceAround,
crossAxisAlignment: CrossAxisAlignment.center,
children: <Widget>[
Container(
width: MediaQuery.of(context).size.width * .3,
child: RaisedButton(
onPressed: () async {
var shouldClear = await showDialog<bool>(
context: context,
builder: (context) {
return generateDialog(context, attemptSave: false);
});
},
child: const Text("Clear"),
),
),
Container(
width: MediaQuery.of(context).size.width * .3,
child: RaisedButton(
onPressed: () async {
await showDialog<bool>(
context: context,
builder: (context) {
return generateDialog(context, attemptSave: true);
});
Navigator.pop(context, true);
},
child: const Text("Save"),
),
)
]),
);
}
}
AlertDialog generateDialog(BuildContext context, {bool attemptSave}) {
return AlertDialog(
title: Center(child: Text("${attemptSave ? "Save" : "Clear"} filter?")),
actions: [
FlatButton(
onPressed: () {
if (attemptSave) {
Navigator.pop(context, false);
} else {
Navigator.pop(context, true);
}
},
child: Text("${attemptSave ? "Save" : "Clear"}"))
],
);
}
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> {
int _counter = 0;
void _incrementCounter() {
setState(() {
_counter++;
});
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Expanded(
child: FilterNavbar(
clearFilter: () {},
)),
Text(
'You have pushed the button this many times:',
),
Text(
'$_counter',
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: 'Increment',
child: Icon(Icons.add),
),
);
}
}