Flutter

@、initialValue不会随setState更新，只能使用controller来控制

使用initialValue来控制，值不会被更新

使用controller来控制，值会变

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    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;
  TextEditingController _controller = TextEditingController();

  void _incrementCounter() {
    setState(() {
      _counter++;
      _controller.text = 'TextFormField - $_counter';
    });
  }

  @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,
            ),
            TextFormField(
              // controller: _controller,
              initialValue: 'TextFormField - $_counter',
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

源码：

field虽然获取到了initialValue，但是下面返回的TextField时用的是controller，而这种情况的_effectiveController实际只在initState方法中使用了initialValue进行初始化，之后就更initialValue没有关联了，因此就算initialValue的值动态改变也不会更新TextFormField的值。