Flutter-方法“调用”在null上被调用

如何解决Flutter-方法“调用”在null上被调用

我正在使用Cloud Firestore作为后端。我已经做了一个表格，想将其数据存储在数据库中。但是，当我按下“保存”按钮时，它会引发以下错误消息：

在处理手势时引发了以下NoSuchMethodError： 方法'call'在null上被调用。 接收者：null 尝试调用：call（“ xyz”）

这是我的代码：

import 'package:flutter/material.dart';
import 'dart:collection';
import 'package:cloud_firestore/cloud_firestore.dart';

class ListPlusForm extends StatefulWidget {
  ListPlusForm({Key key}) : super(key: key);

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

class _ListPlusFormState extends State<ListPlusForm> {
  final _formKey = GlobalKey<FormState>();

  String _itemName;
  double _progress = 0;
  DateTime _start = new DateTime.now();
  DateTime _due;
  int _id = 123;
  bool _sliderSwitch;
  bool _reminderSwitch;
  bool _prioritySwitch;

  @override
  Widget build(BuildContext context) {
    return SizedBox(
      width: MediaQuery.of(context).size.width,height: 235,child: Container(
        decoration: BoxDecoration(
          shape: BoxShape.rectangle,borderRadius: BorderRadius.circular(20.0),gradient: LinearGradient(
            begin: Alignment.topLeft,end: Alignment.bottomRight,colors: [Colors.white,Colors.grey[400]],),child: Form(
          key: _formKey,child: Stack(
            children: [
              Positioned(
                top: 10,left: 10,child: Container(
                  width: 200,child: TextFormField(
                      style: TextStyle(
                        fontSize: 15,decoration: InputDecoration(
                        hintText: 'Name?',onSaved: (val) => {
                            setState(() => _itemName = val),}),Positioned(
                top: 60,child: Row(
                  children: [
                    Text('Need a slider?'),Switch(
                      value: true,onChanged: (value) => {
                        setState(() => _sliderSwitch),},Text('Need a reminder?'),onChanged: (value) => {
                        _reminderSwitch = value,],Positioned(
                top: 90,child: Row(
                  children: [
                    Container(
                      width: 200,child: TextFormField(
                        style: TextStyle(
                          fontSize: 15,decoration: InputDecoration(
                          hintText: 'Due when?',onTap: () => {
                          showDatePicker(
                                  context: context,initialDate: _start,firstDate: _start,lastDate: DateTime(2025))
                              .then(
                            (due) {
                              setState(
                                () {
                                  _due = due;
                                },);
                            },Text('This a priority?'),onChanged: (value) => {
                        _prioritySwitch = value,Positioned(
                top: 140,child: Row(
                  children: [],Positioned(
                  bottom: 5,left: 65,child: Container(
                    width: 200,height: 40,decoration: BoxDecoration(
                      borderRadius: BorderRadius.circular(20.0),gradient: LinearGradient(
                          begin: Alignment.topLeft,colors: <Color>[
                            const Color(0xFF5761B2),const Color(0xFF1FC588),]),child: MaterialButton(
                      child: Row(
                          mainAxisAlignment: MainAxisAlignment.center,children: [
                            Icon(Icons.add_circle),Text('Add item'),onPressed: () => {
                        setState(() {
                          if (_formKey.currentState.validate()) {
                            _formKey.currentState.save();
                            Map<dynamic,dynamic> listItem =
                                new HashMap<dynamic,dynamic>();
                            listItem["Description"](_itemName);
                            listItem["Due"](_due);
                            listItem["ID"](_id);
                            listItem["Priority"](_prioritySwitch);
                            listItem["Progress"](_progress);
                            listItem["Reminder"](_reminderSwitch);
                            listItem["SliderSwitch"](_sliderSwitch);
                            listItem["Start"](_start);

                            Future<void> uploadingData(
                                var _itemName,var _due,var _id,bool _prioritySwitch,var _progress,bool _reminderSwitch,bool _sliderSwitch) async {
                              await Firestore.instance
                                  .collection("Task Lists")
                                  .add(listItem);
                            }
                          }
                          ;
                        }),))
            ],);
  }
}

谢谢！

解决方法

问题是您调用了HashMap的键而不是将其归因于

ip2 = open('rotten','r')
ipList1 = [line.strip().replace('\n','') for line in ip1]
ipList2 = [line.strip().replace('\n','') for line in ip2]
ip1.close()
ip2.close()
newlist = []
for v in ip1:
    if v not in ip2:
        newlist.append(v)

c = open('end','w')
c.write('\n'.join(newlist))
c.close()

更改

listItem["Description"](_itemName);
listItem["Due"](_due);
listItem["ID"](_id);
listItem["Priority"](_prioritySwitch);
listItem["Progress"](_progress);
listItem["Reminder"](_reminderSwitch);
listItem["SliderSwitch"](_sliderSwitch);
listItem["Start"](_start);