flutter - 引发了一个异常:NoSuchMethodError:在null上调用了getter 'the0'

Question

我正在尝试使用Rest Service从API获取数据。
但是我得到一个错误，说getter被调用为null，在进行了一些研究之后，我发现了一些东西，例如UI，要显示的数据比getData函数先执行，它使系统将变量读取为null并且发生错误。任何人都可以帮我解决这个问题。

这是我的一些代码，

class PickUp extends StatefulWidget {
  var created_name, wmsorders_id, id;
  PickUp(
      {Key key,
      @required this.created_name,
      @required this.wmsorders_id,
      @required this.id})
      : super(key: key);

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

class _PickUpState extends State<PickUp> {
  DetailModel detailModel;
  String sender = "";

  Future<String> getDetail() async {
    print("id : " + widget.id);
    var data = "id=" + widget.id + "";
    var response_detail = await RestService()
        .restRequestServiceGet(SystemParam.URL_DETAIL_UPCOMING, data);
    print("response_detail : " + response_detail.body.toString());

    setState(() {
      detailModel = DetailModel.fromJson(jsonDecode(response_detail.body));

    });

    return "Success!";
  }

  @override
  void initState() {
    getDetail();
  }

  Widget build(BuildContext context) {

    // NULL CHECKING
    if (detailModel != null) {
          print("sender =" +detailModel.the0.picName);
    } else {
          print("sender = null");
    }

     // I want to get picName from detail Model and using it in UI, but I got Error here

    sender = detailModel.the0.picName'; 
    print("sender = " +'$sender');

}

这是detailModel

// To parse this JSON data, do
//
//     final detailModel = detailModelFromJson(jsonString);

import 'dart:convert';

DetailModel detailModelFromJson(String str) => DetailModel.fromJson(json.decode(str));

String detailModelToJson(DetailModel data) => json.encode(data.toJson());

class DetailModel {
    The0 the0;
    The0 the1;
    Records records;

    DetailModel({
        this.the0,
        this.the1,
        this.records,
    });

    factory DetailModel.fromJson(Map<String, dynamic> json) => DetailModel(
        the0: The0.fromJson(json["0"]),
        the1: The0.fromJson(json["1"]),
        records: Records.fromJson(json["records"]),
    );

    Map<String, dynamic> toJson() => {
        "0": the0.toJson(),
        "1": the1.toJson(),
        "records": records.toJson(),
    };
}

class Records {
    int status;
    String message;

    Records({
        this.status,
        this.message,
    });

    factory Records.fromJson(Map<String, dynamic> json) => Records(
        status: json["status"],
        message: json["message"],
    );

    Map<String, dynamic> toJson() => {
        "status": status,
        "message": message,
    };
}

class The0 {
    String id;
    String sku;
    int sak;
    String qty;
    String shipstatId;
    String picName;
    String picTelp;
    String orderMultipleId;
    String orderdetId;
    String coordinatorId;

    The0({
        this.id,
        this.sku,
        this.sak,
        this.qty,
        this.shipstatId,
        this.picName,
        this.picTelp,
        this.orderMultipleId,
        this.orderdetId,
        this.coordinatorId,
    });

    factory The0.fromJson(Map<String, dynamic> json) => The0(
        id: json["id"],
        sku: json["sku"],
        sak: json["sak"],
        qty: json["qty"],
        shipstatId: json["shipstat_id"],
        picName: json["pic_name"],
        picTelp: json["pic_telp"],
        orderMultipleId: json["order_multiple_id"],
        orderdetId: json["orderdet_id"],
        coordinatorId: json["coordinator_id"],
    );

    Map<String, dynamic> toJson() => {
        "id": id,
        "sku": sku,
        "sak": sak,
        "qty": qty,
        "shipstat_id": shipstatId,
        "pic_name": picName,
        "pic_telp": picTelp,
        "order_multiple_id": orderMultipleId,
        "orderdet_id": orderdetId,
        "coordinator_id": coordinatorId,
    };
}

这是错误，

Answer 1

您需要在构建方法中使用FutureBuilder，然后等待响应。

删除setstate并按如下所示修改代码。

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          'Test',
          style: TextStyle(
            color: Colors.white,
          ),
        ),
      ),
      body: FutureBuilder<DetailModel>(
        future: getDetail(),
        builder: (context, snapshot) {
          if (snapshot.hasData) {
             print("Here you can get data "+snapshot.data.toString());
          } else {
            print("Waiting mode");
            return Container(
              color: Colors.blue,
            );
          }
        },
      ),
    );
  }
}