我对Flutter还是个新手。我从来没有使用过Visibility类。我在代码中乱用了它，但我似乎无法让它工作，直到按下复选框才能隐藏“祝贺”，并在按下确切的复选框时使滑块消失。我已经包含了一个视频，说明我需要完成什么。请帮助！

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: Scaffold(
        appBar: AppBar(title: const Text(_title)),
        body: const MyStatefulWidget(),
      ),
    );
  }
}

class LabeledCheckbox extends StatelessWidget {
  const LabeledCheckbox({
    super.key,
    required this.label,
    required this.padding,
    required this.value,
    required this.onChanged,
  });

  final String label;
  final EdgeInsets padding;
  final bool value;
  final ValueChanged<bool> onChanged;

  @override
  Widget build(BuildContext context) {
    return InkWell(
      onTap: () {
        onChanged(!value);
      },
      child: Padding(
        padding: padding,
        child: Row(
          children: <Widget>[
            Checkbox(
              value: value,
              onChanged: (bool? newValue) {
                onChanged(newValue!);
              },
            ),
            Expanded(child: Text(label)),
          ],
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({super.key});

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  bool _isSelected = false;
   double _currentSliderValue = 0;
   bool _isVisible = true;


  @override
  Widget build(BuildContext context) {  
    return Form(
      key: _formKey,
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          TextFormField(
            decoration: const InputDecoration(
              hintText: 'First Name',
            ),
            validator: (String? value) {
              if (value == null || value.isEmpty) {
                return 'Please Enter First Name';
              }
              return null;
            },
          ),
           TextFormField(
            decoration: const InputDecoration(
              hintText: 'Last Name',
            ),
            validator: (String? value) {
              if (value == null || value.isEmpty) {
                return 'Please Enter Last Name';
              }
              return null;
            },
          ),
          CheckboxListTile(
          title: const Text("I am graduating this semester"),
          value: _isSelected,  
          onChanged: (value) {  
              setState(() {  
              _isSelected = value!; 
              _isVisible = !_isVisible;
              
                    });  
                  }, 
          ),

          Visibility(
              child:  Text("Congratulations!!",
                style: TextStyle(fontSize: 30, color: Colors.green))),
          Center(
          child: Text("How many classes are you planning to take this semester")  
      ),  
          Slider(
          label: _currentSliderValue.round().toString(),
          value: _currentSliderValue,
          max: 8,
          divisions: 8,
          onChanged: (value) {
          setState(() {
            _currentSliderValue = value;
          });
        },
         
      ),
          Padding(
            padding: const EdgeInsets.symmetric(vertical: 16.0),
            child: ElevatedButton(
              onPressed: () {
                
                // Validate will return true if the form is valid, or false if
                // the form is invalid.
                if (_formKey.currentState!.validate()) {
                   ScaffoldMessenger.of(context).showSnackBar(
                    const SnackBar(content: Text('Thank you for submitting the survey!')),
                  );
                  // Process data.
                }
              },
              child: const Text('Submit'),
            ),
          ),
        ],
      ),
  
      
    ); 
  }
}

Link to Video example