NoSuchMethodError：吸气剂“头像”在null上被调用

问题描述

看过类似的问题，看不到任何常见的错误。一旦工厂似乎可以毫无问题地创建对象。但是，调用任何方法都会生成NoSuchMethodError。调试了好几天，没了主意。可以使用具有一般布局的数据模型的类似代码，而不会出现任何问题。

这是数据模型的代码

class Performer {
  String avatar,header,name,username;
  int id,subscribePrice;
  bool isRealPerformer,isPerformer,hasStories,hasStream,isPaywallRestriction;

  Performer(
      {this.avatar,this.header,this.name,this.username,this.id,this.subscribePrice,this.isRealPerformer,this.isPerformer,this.hasStories,this.hasStream,this.isPaywallRestriction});

  factory Performer.fromJson(Map<String,dynamic> performer) {
    return Performer(
        avatar: performer["avatar"],header: performer["header"],name: performer["name"],username: performer["username"],id: performer["id"],subscribePrice: performer["subscribePrice"],isRealPerformer: performer["isRealPerformer"],isPerformer: performer["isPerformer"],hasStories: performer["hasStories"],hasStream: performer["hasStream"],isPaywallRestriction: performer["isPaywallRestriction"]);
  }
}

这是填充模型的代码

Future<List<Performer>> getSubscriptions() async {
    List<Performer> performers = [];

    String url = "some API url";

    String res = await _callServer(url);

    if (res.isNotEmpty) {
      List<dynamic> payload = json.decode(res);

      payload.forEach((element) {
        performers.add(new Performer.fromJson(element));
      });
      return performers;

    } else return performers;
  }

Future<Performer> getPerformer(int performerID) async {
    List<Performer> subs = await getSubscriptions();

    Performer performer;

    int prefIndex;

    for (int x = 0; x < subs.length; x++) {
      if (subs[x].id == performerID){
        performer = subs[x];
        break;
      }
    }

    if (performer.avatar != null) {
      print("found ${performer.username}");
      return performer;
    } else return null;
  }

这是基于模型生成UI元素的代码

class ProfilePic extends StatefulWidget {
  final int id;
  ProfilePic({Key key,@required this.id}) : super();

  @override
  State<StatefulWidget> createState() => _profilePicState();
}

class _profilePicState extends State<ProfilePic> {
  Performer performer;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    Backend().getPerformer(widget.id).then((value) {
      performer = value;
      setState(() {});
    });

  }

  @override
  Widget build(BuildContext context) {
    print("profile for: ${widget.id}");
    return Container(
      child: performer == null ? Container() : CircleAvatar(
        radius: 30.0,backgroundImage:
        NetworkImage(performer.avatar),backgroundColor: Colors.transparent,),);
  }

解决方法

在您的getSubscriptions中，尝试

payload.forEach((element) {
        performers.add(new Performer.fromJson(Map.from(element)));
});

,

代码没什么问题，是将帖子ID而非用户ID返回给函数，因此返回空错误。