Flutter页面参数的传递（获取&返回），比如修改昵称头像，并在上一级页面返回显示

在项目中经常需要返回特定数据，或者传递参数给上一页

返回1

 onPressed: () {
            Map infos = {};
            infos["nickname"] = nicknamelast;
            infos["avatar"] = avatar;
            Navigator.of(context).pop(infos);
          }

返回2

Flutter中可以通过WillPopScope来实现返回按钮拦截

onWillPop是一个WillPopScope的回调函数，当用户点击返回按钮时被调用

WillPopScope必须包含child，否则会报错

 WillPopScope(
 
child:...,


onWillPop: () {
        Map infos = {};
        infos["nickname"] = nicknamelast;
        infos["avatar"] = avatar;
        Navigator.of(context).pop(infos);
      },
      

源码：

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// @dart = 2.8

import 'framework.dart';
import 'navigator.dart';
import 'routes.dart';

///为用户否决尝试注册一个回调，以取消封闭
///[ModalRoute]。
///
///也可以看看：
///
///*[ModalRoute.addScopedWillPopCallback]和[ModalRoute.removeScopedWillPopCallback]，
///此小部件用来注册和注销[onWillPop]的代码。 
class WillPopScope extends StatefulWidget {
  ///创建一个小部件，该小部件注册用户对否决尝试的回调
  ///关闭封闭的[ModalRoute]。
  ///
  ///[child]参数不能为null。 
  const WillPopScope({
    Key key,
    @required this.child,
    @required this.onWillPop,
  })  : assert(child != null),
        super(key: key);

  /// The widget below this widget in the tree.
  ///
  /// {@macro flutter.widgets.child}
  final Widget child;

  ///由用户调用否决尝试以消除封闭的[ModalRoute]。
   ///
   ///如果回调返回的Future解析为false，则包含
   ///不会弹出路线。
  final WillPopCallback onWillPop;

  @override
  _WillPopScopeState createState() => _WillPopScopeState();
}

class _WillPopScopeState extends State<WillPopScope> {
  ModalRoute<dynamic> _route;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    if (widget.onWillPop != null)
      _route?.removeScopedWillPopCallback(widget.onWillPop);
    _route = ModalRoute.of(context);
    if (widget.onWillPop != null)
      _route?.addScopedWillPopCallback(widget.onWillPop);
  }

  @override
  void didUpdateWidget(WillPopScope oldWidget) {
    super.didUpdateWidget(oldWidget);
    assert(_route == ModalRoute.of(context));
    if (widget.onWillPop != oldWidget.onWillPop && _route != null) {
      if (oldWidget.onWillPop != null)
        _route.removeScopedWillPopCallback(oldWidget.onWillPop);
      if (widget.onWillPop != null)
        _route.addScopedWillPopCallback(widget.onWillPop);
    }
  }

  @override
  void dispose() {
    if (widget.onWillPop != null)
      _route?.removeScopedWillPopCallback(widget.onWillPop);
    super.dispose();
  }

  @override
  Widget build(BuildContext context) => widget.child;
}

接受

 onPressed: () {
                        Navigator.pushNamed(context, route.OpenPersonInfoPage)
                            .then((value) {
                          setState(() {
                            print(value.toString());

                            Map agrs = value;
                            Config.UInfo.nickname = agrs["nickname"];
                            Config.UInfo.avatar = agrs["avatar"];
                          });

这样的话，就可以在按返回按钮的时候返回数据，

在这儿还可以向大家介绍如何双击退出程序

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:fluttertoast/fluttertoast.dart';
 
void main() {
  runApp(MyApp());
}
 
class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return WillPopTest();
  }
}
 
class WillPopTest extends State {
  DateTime _lastTime;
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          backgroundColor: Colors.blue,
          centerTitle: true,
          title: Text(
            '实现二次点击退出',
            style: TextStyle(fontSize: 18, color: Colors.white),
          ),
        ),
        body: WillPopScope(
          onWillPop: ()async{
            if(_lastTime==null||DateTime.now().difference(_lastTime)>Duration(seconds: 1)){
              _lastTime=DateTime.now();
              Fluttertoast.showToast(msg: "再点击一次退出app",
                fontSize: 16,
                backgroundColor: Colors.blue,
                textColor: Colors.white
              );
              return false;
            }
            return true;
          },
          child: Container(
            alignment: Alignment.center,
            child: Text(
              "1秒内连续按两次返回键退出",
              style: TextStyle(fontSize: 30),
            ),
          ),
        ),
      ),
    );
  }
}