只需使用表单验证，在TextFormField编辑验证器函数中，添加onChange函数并调用setState以获取inputtedValue，该值也可以保留禁用按钮，除非表单经过验证。
需要注意的要点：
1.使用final _formKey = GlobalKey<FormState>();
1.其中String? inputtedValue;和!userInteracts()是窍门，可以参考代码;
1.当ElevatedButton onPressed方法为null时，按钮将被禁用。只需传入条件!userInteracts() || _formKey.currentState == null || !_formKey.currentState!.validate()
验证码：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyCustomForm(),
    );
  }
}

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

  @override
  MyCustomFormState createState() {
    return MyCustomFormState();
  }
}

// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
  // Create a global key that uniquely identifies the Form widget
  // and allows validation of the form.
  //
  // Note: This is a GlobalKey<FormState>,
  // not a GlobalKey<MyCustomFormState>.
  final _formKey = GlobalKey<FormState>();

  // recording fieldInput
  String? inputtedValue;

  // you can add more fields if needed
  bool userInteracts() => inputtedValue != null;

  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return Scaffold(
      appBar: AppBar(
        title: const Text('Form Disable Button Demo'),
      ),
      body: Form(
        key: _formKey,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            TextFormField(
              // The validator receives the text that the user has entered.
              validator: (value) {
                if (inputtedValue != null && (value == null || value.isEmpty)) {
                  return 'Please enter some text';
                }
                return null;
              },
              onChanged: (value) => setState(() => inputtedValue = value),
            ),
            Padding(
              padding: const EdgeInsets.symmetric(vertical: 16.0),
              child: ElevatedButton(
                // return null will disable the button
                // Validate returns true if the form is valid, or false otherwise.
                onPressed: !userInteracts() || _formKey.currentState == null || !_formKey.currentState!.validate() ? null :() {
                  // If the form is valid, display a snackbar. In the real world,
                  // you'd often call a server or save the information in a database.
                  ScaffoldMessenger.of(context).showSnackBar(
                    SnackBar(content: Text('Processing Data: ' + inputtedValue!)),
                  );
                },
                child: const Text('Submit'),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

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我认为更好的方法是为按钮的onPressed参数分配空值。请查看下面的链接。https://www.flutterbeads.com/disable-button-in-flutter/

你有自定义的小部件，所以我不知道你的小部件是如何工作的，但在这里你可以使用AbsorbPointer禁用一个按钮，并检查你的textformfield文本在onChange参数像这里;

bool isDisabled = true;

  String _validateUserName(value) {
    if (value!.isEmpty) {
      return ValidatorString.userNameRequired;
    } else if (value.trim().length < 3) {
      return ValidatorString.userNameTooShort;
    } else if (value.trim().length > 20) {
      return ValidatorString.userNameTooLong;
    } else {
      setState(() {
        isDisabled = false;
      });
      return null;
    }
  }
  @override
  Widget build(BuildContext context) {
    final ButtonStyle style =
        ElevatedButton.styleFrom(textStyle: const TextStyle(fontSize: 20));

    return Center(
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          ElevatedButton(
            style: style,
            onPressed: null,
            child: const Text('Disabled'),
          ),
          const SizedBox(height: 30),
          TextFormField(
            decoration: const InputDecoration(
              labelText: 'Label',
            ),
            onChanged: (String value) {
              _validateUserName(value);
            },
          ),
          AbsorbPointer(
            absorbing: isDisabled, // by default is true
            child: TextButton(
              onPressed: () {},
              child: Text("Button Click!!!"),
            ),
          ),
        ],
      ),
    );
  }

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禁用按钮的方法总是将null传递给onPressed回调，您可以使用按钮主题来设置这些样式。

ProgressButton(
              isLoading: isLoading,
              onPressed: _formKey.currentState?.validate() == true ? () {
                // saveEvent();
              } : null,
              label: isEditing ? 'Save' : 'Create',
            ),

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更好的方法是在流中的某个地方保存一个布尔值并更新它