只需重建一个文本小部件。但仍然占用与重建整个屏幕相同的资源

Question

我刚刚使用provider：4.0.5进行了测试，将textview拆分为其他类，并使用consumer为文本重建提供状态，但也许所有小部件也都已重建。我的代码：

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

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

class MyState with ChangeNotifier {
  int counter = 0;

  void incre() {
    counter++;
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: ChangeNotifierProvider(
          create: (_) => MyState(),
          child: 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> {

  @override
  Widget build(BuildContext context) {
    print('build');
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Opacity(
              opacity: 0.5,
              child: Opacity(
                opacity: 0.5,
                child: Container(
                  decoration: BoxDecoration(color: Colors.red, boxShadow: [
                    BoxShadow(
                        color: Colors.yellow,
                        offset: Offset(-5, -5),
                        blurRadius: 25,
                        spreadRadius: 25)
                  ]),
                  child: Center(
                    child: Text(
                      'Hello World',
                      style: Theme.of(context).textTheme.headline4,
                    ),
                  ),
                ),
              ),
            ),
            Opacity(
              opacity: 0.5,
              child: Opacity(
                opacity: 0.5,
                child: Container(
                  decoration: BoxDecoration(color: Colors.red, boxShadow: [
                    BoxShadow(
                        color: Colors.yellow,
                        offset: Offset(-5, -5),
                        blurRadius: 25,
                        spreadRadius: 25)
                  ]),
                  child: Center(
                    child: Text(
                      'Hello World',
                      style: Theme.of(context).textTheme.headline4,
                    ),
                  ),
                ),
              ),
            ),
            Opacity(
              opacity: 0.5,
              child: Opacity(
                opacity: 0.5,
                child: Container(
                  decoration: BoxDecoration(color: Colors.red, boxShadow: [
                    BoxShadow(
                        color: Colors.yellow,
                        offset: Offset(-5, -5),
                        blurRadius: 25,
                        spreadRadius: 25)
                  ]),
                  child: Center(
                    child: Text(
                      'Hello World',
                      style: Theme.of(context).textTheme.headline4,
                    ),
                  ),
                ),
              ),
            ),
            Opacity(
              opacity: 0.5,
              child: Opacity(
                opacity: 0.5,
                child: Container(
                  decoration: BoxDecoration(color: Colors.red, boxShadow: [
                    BoxShadow(
                        color: Colors.yellow,
                        offset: Offset(-5, -5),
                        blurRadius: 25,
                        spreadRadius: 25)
                  ]),
                  child: Center(
                    child: Text(
                      'Hello World',
                      style: Theme.of(context).textTheme.headline4,
                    ),
                  ),
                ),
              ),
            ),
            SizedBox(
              height: 35,
            ),
            MyText(),
            RaisedButton(
              onPressed: Provider.of<MyState>(context, listen: false).incre,
//              onTap: () {
//                setState(() {});
//              },
              child: Text('click'),
            )
          ],
        ),
      ),
    );
  }
}

class MyText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Consumer<MyState>(
      builder: (_, state, __) {
        print('buildText2');
        return Text(
          'You have pushed the button this many times: ${state.counter}',
        );
      },
    );
  }
}

这是我仅更新和重建文本时的屏幕，但这非常昂贵。

这是我扑扑的医生-v

[✓] Flutter（在Mac OS X 10.15.4 19E287上为Channel dev，v1.18.0-6.0.pre，语言环境为en-VN）•位于/ Users / tbm / dev / flutter_sdk / flutter的Flutter 1.18.0-6.0.pre版•框架修订版84c84fb249（6天前），2020-04-20 21:35:01 -0400•引擎版本2bde4f0ae4•Dart版本2.9.0（内部版本2.9.0-1.0.dev a12c36dd97）

Answer 1

避免不必要的重建可以优化CPU时间。您的问题是渲染时间，该时间不受您所做的优化的影响。

您的问题是由于您的用户界面过于复杂而无法绘制。

原因之一是：Opacity非常昂贵，而您使用了[[很多。

代替做：

Opacity(
  opacity: .5
  child: Opacity(
    opacity: .5
    child: ...
  ),
),

第一步是将两个Opacity合并为一个：
Opacity(
  opacity: .5 * .5
  child: ...
),

然后，为进一步优化，而不是：
[
  Opacity(
    opacity: .5 * .5
    child: A(),
  ),
  Opacity(
    opacity: .5 * .5
    child: B(),
  ),
  Something(),
]

您可能有：
[
  Opacity(
    opacity: .5 * .5,
    child: Column(
      mainAxisSize: MainAxisSize.min,
      children: [
        A(),
        B(),
      ],
    ),
  ),
  Something(),
]