Question

我正在使用两个 api，但我在 set State 和 jsonDecode 上出错，我在这里提到过

错误是 getter 'length' 被调用为 null。接收者：空尝试调用：长度

我正在使用两个 api，但我在 set State 和 jsonDecode 上出错，我在这里提到过

错误是 getter 'length' 被调用为 null。接收者：空尝试调用：长度

import 'dart:convert';

import 'package:flutter/material.dart';
import 'package:hospital/CartPage/pages/cartPage.dart';
import 'package:hospital/Drawer/dropdown_menu.dart';
import 'package:hospital/SecondSection/Appointment/AppointmentStatus/appointment_status.dart';
import 'package:hospital/constant.dart';
import 'package:hospital/customApiVariable.dart';
import 'package:http/http.dart' as http;

class Appointment extends StatefulWidget {
  @override
  _AppointmentState createState() => _AppointmentState();
}

class _AppointmentState extends State<Appointment> {
  bool _isLoading = true;

  List<dynamic> diseaseListJson;
  List<dynamic> doctorListJson;

  @override
  void initState() {
    super.initState();
    fetchData();
  }

  Future fetchData() async {
    setState(() {
      _isLoading = true;
    });

    final results = await Future.wait([
      http.get(Uri.parse(
          '$hospitalBaseUrl/doctorListApi.php?a2rTokenKey=$a2rTokenKey')),
      http.get(Uri.parse(
          '$hospitalBaseUrl/diseaseCatApi.php.php?a2rTokenKey=$a2rTokenKey')),
    ]);
   
    print(results[0]);
    print(results[1]);

    setState(() {                                                       //Here
      diseaseListJson = jsonDecode(results[0].body);                     //Here
      doctorListJson = jsonDecode(results[1].body);
//Here
    });

    setState(() {
      _isLoading = false;
    });
  }


//select date part
  DateTime selectedDate = DateTime.now();
  Future<void> _selectDate(BuildContext context) async {
    final DateTime picked = (await showDatePicker(
        context: context,
        initialDate: selectedDate,
        firstDate: DateTime(2015, 8),
        lastDate: DateTime(2101)));
    if (picked != null && picked != selectedDate)
      setState(() {
        selectedDate = picked;
      });
  }

 
  String diseaseChoose;
  String doctorChoose;


  //Select online/htc
  List listOnline = [
    // "Select Disease",
    "Online",
    "HTC",
  ];
  String onlineChoose;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          backgroundColor: kGreen,
          title: Text(
            "Book Appointment",
            style: TextStyle(fontStyle: FontStyle.italic),
          ),
          actions: [
            IconButton(
              icon: Icon(Icons.shopping_cart),
              // onPressed: () => print("open cart"),
              onPressed: () {
                Navigator.push(
                  context,
                  MaterialPageRoute(builder: (context) => Cartpage()),
                );
              },
            ),
            DropDownMenu(),
          ],
        ),
        body: SingleChildScrollView(
          child: Card(
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.only(
                bottomRight: Radius.circular(15),
                bottomLeft: Radius.circular(15),
              ),
            ),
            elevation: 5,
            child: Column(
              children: [
//This is Select Disease part

                Padding(
                  padding: const EdgeInsets.only(left: 26, right: 26, top: 20),
                  child: Card(
                    shape: BeveledRectangleBorder(
                      borderRadius: BorderRadius.circular(6.9),
                    ),
                    elevation: 4,
                    shadowColor: kGreen,
                    child: Container(
                      padding: EdgeInsets.only(left: 10),
                      decoration: BoxDecoration(
                        border: Border.all(color: Colors.grey, width: 1),
                        borderRadius: BorderRadius.circular(10),
                      ),
                      child: DropdownButton(
                          hint: Text("Select Disease"),
                          dropdownColor: Colors.white,
                          icon: Icon(Icons.arrow_drop_down),
                          iconSize: 36,
                          isExpanded: true,
                          underline: SizedBox(),
                          style: TextStyle(color: Colors.black, fontSize: 22),
                          value: diseaseChoose,
                          onChanged: (newValue) {
                            setState(() {
                              diseaseChoose = newValue;
                            });
                          },
                          items: List.generate(
                              diseaseListJson.length,
                              (index) => DropdownMenuItem(
                                  value: diseaseListJson[index]['name'],
                                  child: Text(diseaseListJson[index]['name']))
                           
                              )),
                    ),
                  ),
                ),

                Padding(padding: EdgeInsets.only(top: 20.0)),
                //This is a select Date part
                Padding(
                  padding: const EdgeInsets.only(left: 26, right: 26),
                  child: InkWell(
                    onTap: () {
                      setState(() {
                        _selectDate(context);
                      });
                    },
                    child: Card(
                      shape: BeveledRectangleBorder(
                        borderRadius: BorderRadius.circular(6.9),
                      ),
                      elevation: 4,
                      shadowColor: kGreen,
                      child: Container(
                        height: 55,
                        decoration: BoxDecoration(
                          border: Border.all(color: Colors.grey, width: 1),
                          borderRadius: BorderRadius.circular(10),
                        ),
                        child: Row(
                          children: <Widget>[
                            Padding(
                              padding: const EdgeInsets.only(left: 10),
                              child: Icon(Icons.calendar_today),
                            ),
                            Padding(
                              padding: const EdgeInsets.only(left: 10),
                              child: Text(
                                // (paymentDate.toString()),
                                // ("${paymentDate.day}/${paymentDate.month}/${paymentDate.year}"),
                                "${selectedDate.toLocal()}".split(' ')[0],
                                style: TextStyle(color: Colors.black87),
                              ),
                            ),
                          ],
                        ),
                      ),
                    ),
                  ),
                ),
                Padding(padding: EdgeInsets.only(top: 20.0)),
//This is select top doctors part
                Padding(
                  padding: const EdgeInsets.only(left: 26, right: 26),
                  child: Card(
                    shape: BeveledRectangleBorder(
                      borderRadius: BorderRadius.circular(6.9),
                    ),
                    elevation: 4,
                    shadowColor: kGreen,
                    child: Container(
                        padding: EdgeInsets.only(left: 10),
                        decoration: BoxDecoration(
                          border: Border.all(color: Colors.grey, width: 1),
                          borderRadius: BorderRadius.circular(10),
                        ),
                        child: DropdownButton(
                            hint: Text("Select Top Dr."),
                            dropdownColor: Colors.white,
                            icon: Icon(Icons.arrow_drop_down),
                            iconSize: 36,
                            isExpanded: true,
                            underline: SizedBox(),
                            style: TextStyle(color: Colors.black, fontSize: 22),
                            value: doctorChoose,
                            onChanged: (newValue) {
                              setState(() {
                                doctorChoose = newValue;
                              });
                            },
                            items: List.generate(
                                doctorListJson.length,
                                (index) => DropdownMenuItem(
                                    value: doctorListJson[index]['doctor_name'],
                                    child: Text(
                                        doctorListJson[index]['doctor_name']))
                                ))),
                  ),
                ),
                Padding(padding: EdgeInsets.only(top: 20.0)),

                //This is select online/htc part
                Padding(
                  padding: const EdgeInsets.only(left: 26, right: 26),
                  child: Card(
                    shape: BeveledRectangleBorder(
                      borderRadius: BorderRadius.circular(6.9),
                    ),
                    elevation: 4,
                    shadowColor: kGreen,
                    child: Container(
                      padding: EdgeInsets.only(left: 10),
                      decoration: BoxDecoration(
                        border: Border.all(color: Colors.grey, width: 1),
                        borderRadius: BorderRadius.circular(10),
                      ),
                      child: DropdownButton(
                        hint: Text("Online/HTC"),
                        dropdownColor: Colors.white,
                        icon: Icon(Icons.arrow_drop_down),
                        iconSize: 36,
                        isExpanded: true,
                        underline: SizedBox(),
                        style: TextStyle(color: Colors.black, fontSize: 22),
                        value: onlineChoose,
                        onChanged: (newValue) {
                          setState(() {
                            onlineChoose = newValue;
                          });
                        },
                        items: listOnline.map((valueOnline) {
                          return DropdownMenuItem(
                              value: valueOnline, child: Text(valueOnline));
                        }).toList(),
                      ),
                    ),
                  ),
                ),
                Padding(padding: EdgeInsets.only(top: 20.0)),
                // Spacer(),
                Padding(
                  padding: const EdgeInsets.only(left: 210.0, bottom: 20),
                  child: Container(
                    decoration: BoxDecoration(
                      borderRadius: BorderRadius.circular(20),
                    ),
                    width: 140,
                    height: 53,
                    child: RaisedButton(
                      elevation: 5,
                      onPressed: () {
                        Navigator.push(
                          context,
                          MaterialPageRoute(
                              builder: (context) => AppointmentStatus()),
                        );
                      },
                      color: kGreen,
                      child: Text(
                        "Book & Pay",
                        style: TextStyle(
                          color: Colors.white,
                          fontSize: 20.0,
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
          ),
        ));
  }
}

Answer 1

我认为您在初始化之前正在使用该列表。您需要在声明列表时对其进行初始化。否则会抛出空错误。

List<dynamic> diseaseListJson=[]; List<dynamic> doctorListJson=[];

getter 'length' 被调用为 null。接收者：空尝试调用：长度

1 个答案: