Flutter 绘制优化

目录

问题描述

在Flutter中当我们要更新一些变量在UI界面上的显示的时候，就需要调用setState方法，这时就会刷新StatefulWidget中的UI，这里就会导致一个问题，因为只要一刷新就会调动此StatefulWidget中所有Widget的刷新，如下所示：

解决方法

可以将需要刷新状态的Widget单独封装为一个StatefulWidget

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});
  final String title;
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            CountWidget(),
          ],
        ),
      ),
    );
  }
}

class CountWidget extends StatefulWidget {
  const CountWidget({Key? key}) : super(key: key);

  @override
  State<CountWidget> createState() => _CountWidgetState();
}

class _CountWidgetState extends State<CountWidget> {
  int _counter = 0;
  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(
          '$_counter',
          style: Theme.of(context).textTheme.headline4,
        ),
        FloatingActionButton(
          onPressed: _incrementCounter,
          tooltip: 'Increment',
          child: const Icon(Icons.add),
        )
      ],
    );
  }
}