如果启用并聚焦以前禁用的TextFormField，我看不到 Flink 的光标。在本例中，TextFormField最初是禁用的，如_enabled状态变量所示，当您单击启用按钮时，该字段将被启用并聚焦，但 Flink 的光标不可见。我必须单击TextFormField才能看到 Flink 的光标。

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: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool _enabled = false;
  FocusNode focusNodeA = FocusNode();

  @override
  Widget build(BuildContext context) {

    return Scaffold(
      appBar: AppBar(
        title: Text('Test'),
      ),
      body: TextFormField(
        enabled: _enabled,
        focusNode: focusNodeA,
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          setState(() => _enabled = true);
          FocusScope.of(context).requestFocus(focusNodeA);
        },
        child: Text('Enable'),
      ),
    );
  }
}

如果我按两次“启用”，则会显示光标。
如果TextFormField已启用并获得焦点，则 Flink 光标可见。