I / flutter（13328）：错误NoSuchMethodError：在null上调用了方法'openRead'

Question

单击“提交”按钮时，我的终端出现此错误：

I/flutter (13328): Error NoSuchMethodError: The method 'openRead' was called on null.
I/flutter (13328): Receiver: null
I/flutter (13328): Tried calling: openRead()

这是我的editAttraction.dart

    import 'dart:convert';
import 'dart:io';

import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:myapp/model/api.dart';
import 'package:myapp/model/attractionModel.dart';
import 'package:http/http.dart' as http;
import 'package:async/async.dart';
import 'package:path/path.dart' as path;
import 'package:shared_preferences/shared_preferences.dart';

class EditAttraction extends StatefulWidget {
  final AttractionModel model;
  final VoidCallback reload;
  EditAttraction(this.model, this.reload);
  @override
  _EditAttractionState createState() => _EditAttractionState();
}

class _EditAttractionState extends State<EditAttraction> {
  final _key = new GlobalKey<FormState>();
  String attractionName, description, price, idUsers;
  File _imageFile;

  _pilihGallery() async{
    var image = await ImagePicker.pickImage(
      source: ImageSource.gallery,
      maxHeight: 1920.0,
      maxWidth: 1080);
      setState(() {
        _imageFile = image;
      });
  }

  TextEditingController txtAttractionName, txtDescription, txtPrice;

  setup() async{
    SharedPreferences preferences = await SharedPreferences.getInstance();
    setState(() {
      idUsers = preferences.getString("id");
    });
    txtAttractionName = TextEditingController(text: widget.model.attractionName);
    txtDescription = TextEditingController(text: widget.model.description);
    txtPrice = TextEditingController(text: widget.model.price);
  }

  check(){
    final form = _key.currentState;
    if (form.validate()) {
      form.save();
      submit();
    } else {

    }
  }

  submit() async {
    try {
      var stream = http.ByteStream(DelegatingStream.typed(_imageFile.openRead()));
      var length = await _imageFile.length();
      var uri = Uri.parse(BaseUrl.editAttraction);
      var request = http.MultipartRequest("POST",uri);
      request.fields['attractionName'] = attractionName;
      request.fields['description'] = description;
      request.fields['price'] = price;
      request.fields['idUsers'] = idUsers;
      request.fields['idAttraction'] = widget.model.id;


      request.files.add(http.MultipartFile("image", stream, length, filename: path.basename(_imageFile.path)));
      var response = await request.send();
      if (response.statusCode > 2) {
        print("image uploaded");
        setState(() {
          widget.reload();
          Navigator.pop(context);
        });

      } else {
        print("image failed to upload");
      }
    } catch (e) {
      debugPrint("Error $e");
    }
    // final response = await http.post(BaseUrl.editAttraction, body : {
    //   "attractionName" : attractionName,
    //   "description" : description,
    //   "price" : price,
    //   "idAttraction" : widget.model.id
    // });
    // final data = jsonDecode(response.body);
    // int value = data['value'];
    // String message = data['message'];

    // if (value == 1) {
    //   setState(() {
    //     widget.reload();
    //     Navigator.pop(context);
    //   });
    // } else {
    //   print(message);
    // }
  }

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Form(
        key: _key,
        child: ListView(
                padding: EdgeInsets.all(16.0),
          children: <Widget>[
            Container(
              width: double.infinity,
              height: 150.0,
              child: InkWell(
                onTap:(){
                  _pilihGallery();
                },
                child: _imageFile == null 
                ? Image.network('http://192.168.42.48/myapp/upload/' + widget.model.image) 
                : Image.file(_imageFile,
                 fit: BoxFit.fill,
                ),
              ),
            ),
            TextFormField(
              controller: txtAttractionName,
              onSaved: (e) => attractionName = e,
              decoration: InputDecoration(
                labelText: "Places Name"
              ),
            ),

            TextFormField(
              controller: txtDescription,
              onSaved: (e) => description = e,
              decoration: InputDecoration(
                labelText: "Description"
              ),
            ),

            TextFormField(
              controller: txtPrice,
              onSaved: (e) => price = e,
              decoration: InputDecoration(
                labelText: "Price"
              ),
            ),

            MaterialButton(
              onPressed: (){
                check();
              }, child: Container(
                  padding: EdgeInsets.all(13),
                  decoration: BoxDecoration(
                    borderRadius: BorderRadius.circular(20),
                    gradient: LinearGradient(
                      begin: Alignment.centerLeft,
                      end: Alignment.centerRight,
                      colors: [
                        Colors.pink,
                        Colors.purple,
                      ]
                    )
                  ),
                  child: Text("Submit", style: TextStyle(color: Colors.white),),
                ),
              )
          ],
        ),
      ),
    );
  }
}

这是我的editAttraction.php

<?php

    require  "../config/connect.php";

    if ($_SERVER['REQUEST_METHOD']=="POST")
    {
        #code...
        $response = array();
        $attractionName = $_POST['attractionName'];
        $description = $_POST['description'];
        $price = $_POST['price'];
        $idAttraction = $_POST['idAttraction'];
        $image = date('dmTHis').str_replace(" ","",basename($_FILES['image']['name']));
        $imagePath = "../upload/".$image;
        move_uploaded_file($_FILES['image']['tmp_name'], $imagePath);
        
        $insert = "UPDATE attraction SET attractionName = '$attractionName', description = '$description', price = '$price', image = '$image' WHERE id = '$idAttraction'";
        if (mysqli_query($con, $insert)) 
        {
            # code...
            $response['value']=1;
            $response['message']="Added!";
            echo json_encode($response);
        } 
        else 
        {
            # code...
            $response['value']=0;
            $response['message']="Failed to added";
            echo json_encode($response);
        }
    }
?>

这是我的deleteAttraction.php，我不知道这是否与错误有关

<?php

    require  "../config/connect.php";

    if ($_SERVER['REQUEST_METHOD']=="POST")
    {
        #code...
        $response = array();
       
        $idAttraction = $_POST['idAttraction'];
        
        $insert = "DELETE FROM attraction WHERE id = '$idAttraction' ";
        if (mysqli_query($con, $insert)) 
        {
            # code...
            $response['value']=1;
            $response['message']="Deleted!";
            echo json_encode($response);
        } 
        else 
        {
            # code...
            $response['value']=0;
            $response['message']="Failed to delete";
            echo json_encode($response);
        }
    }
?>

在此之前（大约2周前），我运行该应用程序，并尝试更新和删除，并且效果很好。但是，现在我再次尝试，更新在终端中出现错误，并且我无法删除应用程序中的任何项目，并且显示消息“无法删除”。

已编辑： 我可以对其进行更新，但必须从上传新图像进行更新，然后才能提交所有内容。

我在编码中写错了吗？我真的需要帮助。