问题
Here is a simple example of code that navigator push for a form called. and pop for an answer. my goal is to make a pop of an object, not a string, but keeping it that simple still doesn't work.
main.dart:
import 'package:flutter/material.dart';
import 'answer.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
final appTitle = 'Form Validation Demo';
return MaterialApp(
title: appTitle,
home: Scaffold(
appBar: AppBar(
title: Text(appTitle),
),
body: ShowData(),
),
);
}
}
// Create a Form widget.
class MyCustomForm extends StatefulWidget {
@override
MyCustomFormState createState() {
return MyCustomFormState();
}
}
// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
// Create a global key that uniquely identifies the Form widget
// and allows validation of the form.
//
// Note: This is a GlobalKey<FormState>,
// not a GlobalKey<MyCustomFormState>.
final _formKey = GlobalKey<FormState>();
final myController = TextEditingController();
String stateData;
@override
void dispose() {
// Clean up the controller when the widget is disposed.
myController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
// Build a Form widget using the _formKey created above.
return Scaffold(
body: Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
TextFormField(
controller: myController,
validator: (value) {
if (value.isEmpty) {
return 'Please enter some text';
}
return null;
},
onSaved: (value){
stateData = value;
},
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: RaisedButton(
onPressed: () {
// Validate returns true if the form is valid, or false
// otherwise.
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
// If the form is valid, display a Snackbar.
Navigator.pop(context,stateData);
// Scaffold.of(context)
// .showSnackBar(SnackBar(content: Text(myController.text)));
// myController.text = 'look at me';
}
},
child: Text('Submit'),
),
),
],
),
),
);
}
}
answer.dart:
import 'package:flutter/material.dart';
import 'main.dart';
class ShowData extends StatefulWidget {
@override
_ShowDataState createState() => _ShowDataState();
}
class _ShowDataState extends State<ShowData> {
String data = 'start';
@override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(onPressed: (){
String holder = getFormData(context);
setState(() {
data = holder;
});
},
elevation: 4,
),
body:Text(data,style: TextStyle(fontSize: 80),));
}
String getFormData(BuildContext context) {
final Future<String> answer = Navigator.push(context,MaterialPageRoute(builder: (context)=>MyCustomForm()));
answer.then((String value) {
return value != null? value: 'empty';
}
);
}
}
when returning from the form error message is :
'package:flutter/src/widgets/text.dart': Failed assertion: line ... pos... 'data!=null': A non-null String must be provided to a Text widget.
回答1:
Add await to receive the result from Future and return the value;
Future<String> getFormData(BuildContext context) async {
final result = await Navigator.push(
context, MaterialPageRoute(builder: (context) => MyCustomForm()));
return Future.value(result);
}
Modify the FloatingActionButton onPressed code to receive Future String
onPressed: () async {
final value = await getFormData(context);
setState(() {
data = value;
});
},
回答2:
And here is a code if you want to pass a data object and not a String:
main.dart:
import 'package:flutter/material.dart';
import 'answer.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
final appTitle = 'Form Validation Demo';
return MaterialApp(
title: appTitle,
home: Scaffold(
appBar: AppBar(
title: Text(appTitle),
),
body: ShowData(),
),
);
}
}
// Create a Form widget.
class MyCustomForm extends StatefulWidget {
@override
MyCustomFormState createState() {
return MyCustomFormState();
}
}
// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
// Create a global key that uniquely identifies the Form widget
// and allows validation of the form.
//
// Note: This is a GlobalKey<FormState>,
// not a GlobalKey<MyCustomFormState>.
final _formKey = GlobalKey<FormState>();
final myController = TextEditingController();
Data stateData = Data();
@override
void dispose() {
// Clean up the controller when the widget is disposed.
myController.dispose();
super.dispose();
}
@override
Widget build(BuildContext context) {
// Build a Form widget using the _formKey created above.
return Scaffold(
body: Form(
key: _formKey,
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
TextFormField(
controller: myController,
validator: (value) {
if (value.isEmpty) {
return 'Please enter some text';
}
return null;
},
onSaved: (value){
stateData.load = value;
},
),
Padding(
padding: const EdgeInsets.symmetric(vertical: 16.0),
child: RaisedButton(
onPressed: () {
// Validate returns true if the form is valid, or false
// otherwise.
if (_formKey.currentState.validate()) {
_formKey.currentState.save();
// If the form is valid, display a Snackbar.
Navigator.pop(context,stateData);
// Scaffold.of(context)
// .showSnackBar(SnackBar(content: Text(myController.text)));
// myController.text = 'look at me';
}
},
child: Text('Submit'),
),
),
],
),
),
);
}
}
class Data {
String load;
}
answer.dart:
import 'package:flutter/material.dart';
import 'main.dart';
class ShowData extends StatefulWidget {
@override
_ShowDataState createState() => _ShowDataState();
}
class _ShowDataState extends State<ShowData> {
String data = 'start';
@override
Widget build(BuildContext context) {
return Scaffold(
floatingActionButton: FloatingActionButton(onPressed: () async {
final holder = await getFormData(context);
setState(() {
data = holder.load;
});
},
elevation: 4,
),
body:Text(data,style: TextStyle(fontSize: 80),));
}
Future<Data> getFormData(BuildContext context) async {
final answer = await Navigator.push(context,MaterialPageRoute(builder: (context)=>MyCustomForm()));
return (Future.value(answer));
}
}
来源：https://stackoverflow.com/questions/62126709/receive-response-from-pop-navigator-in-flutter