无状态与有状态重建

Question

when a stateless widget is inside a stateful widget it will redraw or not? now the stateless widget can't be redrawn at run time but stateful can. the question is when the stateless widget is inside a stateful widget it will be redrawn or not?

Answer 1

A statelessWidget which is a child of a statefulWidget will be rebuilt if the statefulWidget rebuilds. Basically, when setState is called in a statefulWidget , the old state is chucked away and the build method runs with the new state. So if a statelessWidget it referenced in the statefulWidget 's build method, yes it will be rebuilt.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    print('Stateful widget built');
    return Scaffold(
      appBar: AppBar(
        title: Text('Example'),
      ),
      body: BodyWidget(),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() {});
        },
        tooltip: 'Set state',
        child: Icon(Icons.add),
      ),
    );
  }
}

class BodyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    print('Stateless widget built');
    return Container(
      child: Text('Stateless widget'),
    );
  }
}

Try this example out, when you hit the Fab, it re setState on the statefulWidget and you will get a print out in the console when each build method is run.