Flutter navigator.push() 对象问题

Question

当使用 Navigator.push() 将一个对象从一个 class 传递到另一个 class 时，该对象即使被声明为非最终对象也不会被修改。

主屏幕：创建了一个对象（userBean）并传递给第一个屏幕第一个屏幕：显示相同的对象（userBean）值，并将相同的对象（userBean）再次传递到第二个屏幕。第二个屏幕：尝试在第二个屏幕中修改相同的对象（userBean），并使用 refreshData.then 方法在第一个屏幕中打印相同的对象（userBean）。

Main.dart
import 'package:flutter/material.dart';
import 'package:flutter_app_poc1/firstSceeen.dart';
import 'package:flutter_app_poc1/secondScreen.dart';
import 'package:flutter_app_poc1/userbean.dart';
void main() => runApp(MyApp());

typedef void refreshCallBack(int index);
class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override

  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      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> {

  UserBean user = new UserBean();

  final List<String> hhList = ["General", "edu"];
  int _counter = 0;

  @override

  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(

        title: Text(widget.title),
      ),

      body: Center(

        child: Column(

          mainAxisAlignment: MainAxisAlignment.center,

          children: <Widget>[

            new FlatButton(

                child: Text("Next Screen"),

                onPressed: () {

                  user.id = 1;

                  user.name = "Ramesh";

                  Future<dynamic> refreshData =

                      Navigator.of(context).push(new MaterialPageRoute<dynamic>(

                    builder: (BuildContext context) {

                      return new FirstScreen(userbean: user);

                    },

                  ));

                  refreshData.then((_) {

                  });

                }),
          ],

        ),

      ),

     );
  }
}


Firstscreen.dart
import 'package:flutter/material.dart';
import 'package:flutter_app_poc1/secondScreen.dart';
import 'package:flutter_app_poc1/userbean.dart';
typedef void refreshCallBack(int index);
class FirstScreen extends StatefulWidget {
  UserBean userbean;
  FirstScreen({Key key, this.userbean}) : super(key: key);

  @override
  _FirstScreenState createState() => _FirstScreenState();

}

class _FirstScreenState extends State<FirstScreen> {

  String userName;

  final List<String> hhList = ["General", "edu"];

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      appBar: AppBar(

        title: Text("first"),

      ),

      body: Center(

        child: Column(

          mainAxisAlignment: MainAxisAlignment.center,

          children: <Widget>[

            new Text(widget.userbean.name),

            new RaisedButton(onPressed: (){

              Future<dynamic> refreshData =

              Navigator.of(context).push(new MaterialPageRoute<dynamic>(

                builder: (BuildContext context) {

                  return new SecondScreen(userbean: widget.userbean);

                },

              ));

              refreshData.then((_) {
                print(widget.userbean.name);
              });
            }),
          ],

        ),

      ),
     );
  }
 }



secondscreen.dart
import 'package:flutter/material.dart';

import 'package:flutter_app_poc1/userbean.dart';

class SecondScreen extends StatefulWidget {

  UserBean userbean;
  SecondScreen({Key key, this.userbean}) : super(key: key);

  @override

  _SecondScreenState createState() => _SecondScreenState();

}

class _SecondScreenState extends State<SecondScreen> {

  UserBean bean = UserBean();

  @override

  Widget build(BuildContext context) {

    bean.name = "suresh";
    return Scaffold(

        appBar: AppBar(

          title: Text("Previous Screen"),

        ),

        body: Center(

          child: new FlatButton(

              child: Text(bean.name),

              onPressed: () {

                print(bean.name);

                widget.userbean = bean;

                Navigator.pop(context, true);

              }),

        ));

  }

}

Answer 1

@Murali

如果你想按照相同的过程传递对象，那么按照下面的过程。

从Navigator.pop再次推送新对象

onPressed: () {
            print("TEST second screen :"+bean.name);

            /// here modifying with new object.
            widget.userbean = bean;

            Navigator.pop(context, widget.userbean);
          }),

在第二个屏幕中从特征方法中获取新对象，如下所示

 Future<UserBean> refreshData =
          Navigator.of(context).push(new MaterialPageRoute<UserBean>(
            builder: (BuildContext context) {
              return new SecondScreen(userbean: widget.userbean);
            },
          ));
          refreshData.then((res) {
            print("TEST First screen : ${res.name}");
          });

然后对象将更改为新值。

Flutter navigator.push() 对象问题

Flutter navigator.push() object issue

flutter

flutter-dependencies