events - 为什么我不能将Flutter TextField onChanged事件值传递给Text？

Question

我正在遵循使用状态小部件的示例，但我无法使其正常运行，从onChanged事件中获取值可与打印功能一起使用，但是当我尝试将值传递给Text时，它将不会被接受，原因是文本不在事件本身之外吗？但它仍然在statfulwidget中

这是我的代码:

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Hello You',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new HelloYou(),
    );
  }
}

class HelloYou extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _HelloYouState();
}

class _HelloYouState extends State<HelloYou> {
  @override
  Widget build(BuildContext context) {
    String name = "";

    return Scaffold(
      appBar: AppBar(
        title: Text("HelloYou App !"),
        backgroundColor: Colors.blueAccent,
      ),
      body: Container(
          padding: EdgeInsets.all(15.0),
          child: Column(
            children: <Widget>[
              TextField(
                onChanged: (string) {
                  setState(() {
                    name = string;
                    print('my text is :$name');
                  });
                },
              ),
              Text('my name $name')
            ],
          )),
    );
  }
}

Answer 1

将字符串变量移出构建。当您将其放入构建中时，setState重新运行构建方法，并且字符串变量消失了。

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Hello You',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new HelloYou(),
    );
  }
}

class HelloYou extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _HelloYouState();
}

class _HelloYouState extends State<HelloYou> {

  String name = "";

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("HelloYou App !"),
        backgroundColor: Colors.blueAccent,
      ),
      body: Container(
          padding: EdgeInsets.all(15.0),
          child: Column(
            children: <Widget>[
              TextField(
                onChanged: (string) {
                  setState(() {
                    name = string;
                    print('my text is :$name');
                  });
                },
              ),
              Text('my name $name')
            ],
          )),
    );
  }
}