flutter - 使用 map 而不是 for 语句使类模型中的列表返回零

Question

当我从服务器返回的数据实现分页 ListView 时，我可以简单地测试这种分页能力并且工作正常，例如通过这段代码我可以通过简单的数据制作列表列:

list.add(
    PostItem((b) =>b
        ..title = 'lorem ipsum'
        ..colorInt = _randomGenerator.nextInt(0xFFFFFFFF)),
    );

return BuiltList.of(list);

现在我正在尝试从服务器获取数据并从中获取数据，例如:

List<PostItem> list = [
  PostItem((b)=>b..title = 'lorem ipsum'),
  PostItem((b)=>b..title = 'lorem ipsum')
];

我得到错误:

List<PostItem> list=[];

final response = await http.get(Constants.getPosts, headers: {"Accept": "application/json"});

final responseString = json.decode(response.body) as List;

List<ContentsModel> responses = responseString.map((j) => 
    ContentsModel.fromJson(j)).toList();

responses.map((post)=>
    list.add(PostItem((b) => b..title = post.title),));

return BuiltList.of(list);

list 的行大小为零:

responses.map((post)=>list.add(PostItem((b) => b..title = post.title),));

我的 ContentsModel 类内容是:

part 'contents_model.g.dart';

@JsonSerializable(nullable: false)
class ContentsModel{
  int id;
  String title;
  String description;

  ContentsModel(this.id, this.postId, this.title, this.description, this.type, this.featuredImages, this.slug, this.lang, this.visit, this.click, this.state, this.createdAt, this.updatedAt, this.categories);

  factory ContentsModel.fromJson(Map<String,dynamic> json)=>_$ContentsModelFromJson(json);
  Map<String,dynamic> toJson()=>_$ContentsModelToJson(this);
}

Answer 1

你需要初始化你的列表，然后再添加一些东西:

List<PostItem> list = [];