我有下面的类设置。我能够存储JSON，但检索它时遇到问题。

import 'package:flutter/material.dart';

class SvItem with ChangeNotifier {
  final String id;
  final String meatType;
  final String meatTypeImg;
  final String meatCut;
  final String duration;
  final String temperatur;
  final List<String> instructions;
  final String notes;
  bool isFavorite;

  SvItem({
    required this.id,
    required this.meatType,
    required this.meatTypeImg,
    required this.meatCut,
    required this.duration,
    required this.temperatur,
    required this.instructions,
    required this.notes,
    this.isFavorite = false,
  });

  factory SvItem.fromJson(Map<String, SvItem> json) {
    return SvItem(
      id: "id",
      meatType: "meatType",
      meatTypeImg: "meatTypeImg",
      meatCut: "meatCut",
      duration: "duration",
      temperatur: "temperatur",
      instructions: "instructions" as List<String>,
      notes: "notes",
      isFavorite: "isFavorite" as bool,
    );
  }

  Map<String, dynamic> toJson() {
    return {
      "id": id,
      "meatType": meatType,
      "meatTypeImg": meatTypeImg,
      "meatCut": meatCut,
      "duration": duration,
      "temperatur": temperatur,
      "instructions": instructions,
      "notes": notes,
      "isFavorite": isFavorite
    };
  }
}

通过这段代码，我可以在sharedpreferences中保存自定义类的示例。

Future saveCustomRecipes(item) async {
  SharedPreferences prefs = await SharedPreferences.getInstance();
  prefs.setString("customRecipesList", jsonEncode(item));
  setState(() {});
}

saveCustomRecipes(customRecipes);

但是我如何检索它并将其保存在customRecipes中呢？
我尝试了以下方法：

getCustomRecipesValues() async {
    customRecipes = await getCustomRecipesState();
    setState(() {});
  }

  Future getCustomRecipesState() async {
    final prefs = await SharedPreferences.getInstance();
    var recipeData = prefs.getString("customRecipesList");
    List<SvItem> customRecipes =
        SvItem.fromJson(jsonDecode(recipeData!)) as List<SvItem>;

    print(customRecipes);
    return customRecipes;
  }

但我得到一个错误：[错误：flutter/运行时/dart_vm_initializer.cc（41）]未处理的异常：类型“List”不是类型“Map〈String，dynamic〉”的子类型