问Flutter jsonDecode返回类型是`dynamic`，而相册工厂方法需要一个`Map<String，dynamic>`

EN

import 'dart:convert';

import 'package:http/http.dart' as http;
import 'package:json_annotation/json_annotation.dart';

part 'http.g.dart';

@JsonSerializable()
class Album {
  final int userId;
  final int id;
  final String title;

  Album({this.userId, this.id, this.title});

  factory Album.fromJson(Map<String, dynamic> json) => _$AlbumFromJson(json);
  Map<String, dynamic> toJson() => _$AlbumToJson(this);
}

Future<Album> fetchAlbum() async {
  var resp = await http.get('https://jsonplaceholder.typicode.com/albums/1');
  var A = Album.fromJson(jsonDecode(resp.body)); // Error line

  print(A.title);
  print(A.toJson());
}