参数类型 'List<Plants>?' 无法分配给参数类型 'List<Plants>'

Question

Widget build(BuildContext context) => Scaffold(
    body: FutureBuilder<List<Plants>>(
      future: PlantsApi.getPlantsLocally(context),
      builder:(context, snapshot) {
        final users = snapshot.data;
        switch (snapshot.connectionState) {
          case ConnectionState.waiting:
            return Center(child: CircularProgressIndicator());
          default:
          if (snapshot.hasError) {
            return Center(child: Text('Some error'),);
          }
          else {
            return buildPlants(users);
          }
        }
      }, 
    ),
  );

我对这个有误。用户是错误

当我将 buildPlants(users) 更改为 buildPlants(users!) 时，出现此错误：

 Error: Member not found: 'fromJson'.
    return body.map<Plants>(Plants.fromJson).toList();
                                   ^^^^^^^^

import 'dart:convert';
import 'package:flutter/cupertino.dart';
import 'package:http/http.dart' as http;
import 'package:oplantapp/model/plantData.dart';

class PlantsApi {
  static Future<List<Plants>> getPlantsLocally(BuildContext context) async {
    final assetBundle = DefaultAssetBundle.of(context);
    final data = await assetBundle.loadString('assets/plants.json');
    final body = json.decode(data);

    return body.map<Plants>(Plants.fromJson).toList();
  }
}

这是我获取的数据

Answer 1

我认为您没有在 Plants class 中实现 Plants.fromJson 方法。参考 official documentation

...
Plants.fromJson(Map<String, dynamic> json)
      : name = json['name'],
        email = json['email'];
...

在 Plants 中实施 Plants.fromJson 方法后。尝试更改您的 return 语句

return body.map<Plants>((e) => Plants.fromJson(e)).toList();

参数类型 'List<Plants>?' 无法分配给参数类型 'List<Plants>'

The argument type 'List<Plants>?' can't be assigned to the parameter type 'List<Plants>'

parsing

json

dart

flutter