我使用的是Laravel API和Flutter应用程序作为客户端。这是一个基本的CRUD应用程序，我能够通过API更新记录，但当涉及到删除记录时，会抛出一个异常，我无法找出问题。
Laravel 8应用程序是这样的

路径\API

Route::apiResource('categories', \App\Http\Controllers\Api\CategoryController::class);

应用程序\Http\控制器\API\类别控制器.php

public function destroy(Category $category)
    {
        $category->delete();
        return response()->noContent();
    }

Flutter App看起来像这样

库\屏幕\类别.dart

import 'package:flutter/material.dart';
import 'package:demo_app/models/category.dart';
import 'package:demo_app/widgets/category_edit.dart';

import 'package:demo_app/providers/category_provider.dart';
import 'package:provider/provider.dart';
// import 'package:http/http.dart' as http;

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

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

class CategoriesState extends State<Categories> {
  @override
  Widget build(BuildContext context) {
    final provider = Provider.of<CategoryProvider>(context);
    List<Category> categories = provider.categories;

    return Scaffold(
        appBar: AppBar(
          title: const Text('Categories'),
        ),
        body: ListView.builder(
                  itemCount: categories.length,
                  itemBuilder: (context, index) {
                    Category category = categories[index];
                    return ListTile(
                      title: Text(category.name),
                      trailing: 
                          Row(
                            mainAxisSize: MainAxisSize.min,
                            children: <Widget>[
                              IconButton(
                                icon: const Icon(Icons.edit),
                                onPressed: () {
                                  showModalBottomSheet(
                                    isScrollControlled: true,
                                    context: context,
                                    builder: (context) {
                                      return CategoryEdit(category, provider.updateCategory); 
                                      });
                                },                         
                      ),
                      IconButton(
                            icon: const Icon(Icons.delete),
                            onPressed: () => showDialog(
                              context: context,
                              builder: (context) {
                                return AlertDialog(
                                  title: const Text('confirmation'),
                                  content: const Text('Are you sure you want to delete?'),
                                  actions: [
                                    TextButton(
                                      onPressed: () => deleteCategory(provider.deleteCategory, category),
                                      child: const Text('Confirm')
                                    ),
                                    TextButton(
                                      onPressed: () => Navigator.pop(context),
                                      child: const Text('Cancel')
                                    ),
                                  ]
                                );
                              }
                              ),                              
                          ),
                            ],
                          ),
                    );
                  },
        )
    );
  }

  Future deleteCategory(Function callback, Category category) async{
    await callback(category);
    if (!mounted) return;
    Navigator.pop(context);
  }

}

库\服务\API.dart

// import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:demo_app/models/category.dart';

// import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

class ApiService{

  ApiService();

  final String baseUrl = 'http://flutter-api.test/api/';

  Future<List<Category>> fetchCategories() async {
    http.Response response =
        await http.get(Uri.parse('${baseUrl}categories'));

    List categories = jsonDecode(response.body);

    return categories.map((category) => Category.fromJson(category)).toList();
  }

  Future <Category> updateCategory(Category category) async {

    // String uri = '${baseUrl}categories/$category.id';
    String uri = '${baseUrl}categories/${category.id}';

    http.Response response = await http.put(Uri.parse(uri),
        headers: {
          HttpHeaders.contentTypeHeader: 'application/json',
          HttpHeaders.acceptHeader: 'application/json',
        },
        body: jsonEncode({'name': category.name}));
 
        if(response.statusCode != 200){
          throw Exception('Error happened on update');
        }

    return Category.fromJson(jsonDecode(response.body));
  }

  Future<void> deleteCategory(id) async {

    String uri = '${baseUrl}categories/$id';    

    http.Response response = await http.delete(Uri.parse(uri));
 
    if(response.statusCode != 204){
      throw Exception('Error happened on delete');
    }

  }
}

库\提供程序\类别提供程序.dart

// import 'dart:io';

import 'package:demo_app/models/category.dart';
import 'package:flutter/material.dart';
import 'package:demo_app/services/api.dart';


class CategoryEdit extends StatefulWidget {
  final Category category;
  final Function categoryCallback;

  const CategoryEdit(this.category, this.categoryCallback, {Key? key}) : super(key: key);

  @override
  CategoryEditState createState() => CategoryEditState();

}

class CategoryEditState extends State<CategoryEdit> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  final categoryNameController = TextEditingController();
  ApiService apiService = ApiService();
  String errorMessage = '';

  @override 
  void initState(){
    categoryNameController.text = widget.category.name;
    super.initState();
  }

  @override
  Widget build(BuildContext context){
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Form(
          key: _formKey,
          child: Column(children: <Widget>[
            TextFormField(
              onChanged: (text) => setState(() => errorMessage = ''),
              controller: categoryNameController,
              validator: (String? value) {
                if (value!.isEmpty) {
                  return 'Enter category name';
                }
                return null;
              },
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
                labelText: 'Category Name',
              ),
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                ElevatedButton(
                  child: const Text('Save'),
                  onPressed: () => saveCategory(context),
                ),
                ElevatedButton(
                  style: ElevatedButton.styleFrom(
                    backgroundColor: Colors.red
                  ),
                  child: const Text('Cancel'),
                  onPressed: () => Navigator.pop(context),
                ),
              ],
            ),
            Text(errorMessage, style: const TextStyle(color: Colors.red),)
          ]
          )
          )
         );
   }
  
  Future saveCategory(BuildContext context) async {
    final form = _formKey.currentState;

    if(!form!.validate())
    {
      return;
    }

    widget.category.name = categoryNameController.text;

    await widget.categoryCallback(widget.category);
    if (!mounted) return;
    Navigator.pop(context);

 }  

}

这是我唯一的例外

flutter: Exception: Error happened on delete