工程關(guān)鍵框架如下：

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

import 'model.dart';

class ModelWidget<T extends WidgetModel> extends StatefulWidget {
  final T model;
  final Widget child;

  //是否自動(dòng)dispose, 默認(rèn)true,false的時(shí)候需要自己管理provider的生命周期
  final bool autoDispose;

  const ModelWidget({
    Key key,
    this.model,
    this.child,
    this.autoDispose = true,
  }) :
//        assert(builder != null || child != null),
        super(key: key);

  @override
  _ModelWidgetState<T> createState() => _ModelWidgetState<T>();
}

class _ModelWidgetState<T extends WidgetModel> extends State<ModelWidget<T>> {
  @override
  void initState() {
    widget.model.init();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    if (widget.autoDispose ?? true) {
      //這種方式ChangeNotifierProvider dispose時(shí),會(huì)調(diào)用notifier的dispose方法
      return ChangeNotifierProvider<T>(
        create: (_) => widget.model..buildContext(context),
        child: widget.child,
      );
    } else {
      return ChangeNotifierProvider.value(
        value: widget.model..buildContext(context),
        child: widget.child,
      );
    }
  }
}

先預(yù)告所有原因都在最后一行： child: widget.child,

簡單Demo如下：

import 'dart:convert';

import 'package:flutter/cupertino.dart';


class GoldInfoProviders extends ChangeNotifier {
  static final GoldInfoProviders shared = GoldInfoProviders._();

  factory GoldInfoProviders() => shared;

  GoldInfoProviders._() {
    //TODO: 用戶退出登錄,重新處理數(shù)據(jù),切換語言也要刷
  }
  ///當(dāng)前金幣數(shù)量
  String goldNumber = "01";
  String goldFormatNumber = "01";
  String goldConvertUSDStr = "01";
  String goldNumberFromServer = "01";///此值用于做動(dòng)畫
}



import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutterdemo/GoldInfoProviders.dart';
import 'package:flutterdemo/GoldNewProviders.dart';
import 'package:flutterdemo/MySecondPage.dart';
import 'package:provider/provider.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {

    return ChangeNotifierProvider(
      create: (context){
        return GoldInfoProviders();
      },
      child: Consumer<GoldInfoProviders>(
        builder: (context,_,child){
          print("被重建了");
          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() {
    Widget a = MySecondPage(title: "測",);
    Navigator.of(context).push(
        CupertinoPageRoute(
          fullscreenDialog: false,
          builder: (_) {
///此處是把框架中的寫法轉(zhuǎn)換過來
            return ChangeNotifierProvider(
                create: (context){
              return GoldNewProviders();

            },
              child: Builder(
                builder: (context) {
                  print("此處需要斷點(diǎn)");
                  return MySecondPage(title: "測",);
                }
              ),
            );
          },
        )
    );
  }

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(

        title: Text(widget.title),
      ),
      body: Center(

        child: Column(

          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            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),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}




import 'package:flutter/material.dart';
import 'package:flutterdemo/GoldNewProviders.dart';
import 'package:flutterdemo/SimpleWidget.dart';
import 'package:provider/provider.dart';

import 'GoldInfoProviders.dart';

class MySecondPage extends StatefulWidget {
  MySecondPage({Key key, this.title}) : super(key: key);


  final String title;

  @override
  _MySecondPageState createState() {
    return _MySecondPageState();
  }
}

class _MySecondPageState extends State<MySecondPage> {
  int _counter = 0;

  void _incrementCounter() {
    GoldInfoProviders.shared.goldNumber = "==";
    GoldInfoProviders.shared.goldFormatNumber = "==";
    GoldInfoProviders.shared.goldConvertUSDStr = "==";
    GoldInfoProviders.shared.goldNumberFromServer = "==";
    GoldInfoProviders.shared.notifyListeners();
  }


  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    print("initState");
  }

  @override
  Widget build(BuildContext context) {
    print("被重建了2");
    return ChangeNotifierProvider(
      create: (context){
        return GoldNewProviders();
      },
        child: Scaffold(
          appBar: AppBar(
            // Here we take the value from the MySecondPage object that was created by
            // the App.build method, and use it to set our appbar title.
            title: Builder(builder: (context){
              print("你不被重建嗎");
              return Text(widget.title);
            }, ),
          ),
          body: Center(
            // Center is a layout widget. It takes a single child and positions it
            // in the middle of the parent.
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text(
                  'You have pushed the button this many times:',
                ),
                Text(
                  '${GoldInfoProviders.shared.goldNumber}',
                  style: Theme.of(context).textTheme.headline4,
                ),
              ],
            ),
          ),
          floatingActionButton: FloatingActionButton(
            onPressed: _incrementCounter,
            tooltip: 'Increment',
            child: Icon(Icons.add),
          ), // This trailing comma makes auto-formatting nicer for build methods.
        ),
      );
  }
}

關(guān)注點(diǎn)是當(dāng) GoldInfoProviders.shared.notifyListeners();通知更新時(shí)，MySecondPage中的"被重建了2"是否會(huì)被打印 重建 此時(shí)可以打印正常重建 也符合常規(guī)業(yè)務(wù)更新邏輯 GoldNewProviders更新 則對(duì)應(yīng)的MySecondPage使用GoldNewProviders的地方也更新。但是沒有使用GoldNewProviders的地方也會(huì)更新 會(huì)造成性能浪費(fèi)

當(dāng)被修改為如下時(shí)

void _incrementCounter() {
    Widget a = MySecondPage(title: "測",);
    Navigator.of(context).push(
        CupertinoPageRoute(
          fullscreenDialog: false,
          builder: (_) {
            return ChangeNotifierProvider(
                create: (context){
              return GoldNewProviders();

            },
              child: Builder(
                builder: (context) {
                  print("此處需要斷點(diǎn)");
                  return a;
                }
              ),
            );
          },
        )
    );
  }

重點(diǎn)return a；和return MySecondPage(title: "測",)
MySecondPage中的“被重建了2”不在會(huì)被打印，

排查好久才排查到這一行。。。。

原理解析：

Element updateChild(Element child, Widget newWidget, dynamic newSlot)中的邏輯

if (hasSameSuperclass && child.widget == newWidget) {
        if (child.slot != newSlot)
          updateSlotForChild(child, newSlot);
        newChild = child;
      } else if (hasSameSuperclass && Widget.canUpdate(child.widget, newWidget)) {
        if (child.slot != newSlot)
          updateSlotForChild(child, newSlot);
        child.update(newWidget);
        assert(child.widget == newWidget);
        assert(() {
          child.owner._debugElementWasRebuilt(child);
          return true;
        }());
        newChild = child;
      }

完全相同不在調(diào)用update 不同則調(diào)用update update中會(huì)調(diào)用rebuild導(dǎo)致重建

return a 返回的是上次創(chuàng)建的完全一樣的widget ,所以不在會(huì)被重建

總結(jié)下來 兩種寫法：各有利弊