如何解决：type 'List<dynamic>' 不是 type 'String' 的子类型

Question

我想更新来自 listofTaskNotApprove class 的图像，它会将 documentsnapshot 对象传递到 EditTaskNotApprove。在我更新图像之前，我需要显示特定的图像，用户将从 listofTaskNotApprove 获得 select 特定信息。问题是如何将当前索引的图像显示到新屏幕中？

ListOfTaskNotAccepted class.

import 'package:carousel_pro/carousel_pro.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:fyp/screen/RecordOfficer/EditTaskNotApprove.dart';
import 'package:fyp/shared/Loading.dart';
import 'package:google_fonts/google_fonts.dart';


class ListOfTaskNotAccepted extends StatefulWidget {
  @override
  _ListOfTaskNotAcceptedState createState() => _ListOfTaskNotAcceptedState();
}
final FirebaseAuth auth = FirebaseAuth.instance;
Stream<QuerySnapshot> getUser(BuildContext context) async* {
  final FirebaseUser rd = await auth.currentUser();
  yield* Firestore.instance.collection("Task").where('uid',isEqualTo: rd.uid).where("verified", isEqualTo: 'TidakSah').snapshots();
}
class _ListOfTaskNotAcceptedState extends State<ListOfTaskNotAccepted> {
  List<NetworkImage> _listOfImages = <NetworkImage>[];
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Aduan Tidak Diterima"),
          backgroundColor: Colors.redAccent,
        ),
      body: Container(
      child: StreamBuilder(
          stream: getUser(context),
          builder: (context, snapshot){
            if (snapshot.hasError || !snapshot.hasData) {
              return Loading();
            } else{
              return ListView.builder(
                  itemCount: snapshot.data.documents.length,
                  itemBuilder: (BuildContext context, int index){
                   DocumentSnapshot da = snapshot.data.documents[index];
                    _listOfImages =[];
                    for(int i =0; i <da['url'].length; i++){
                      _listOfImages.add(NetworkImage(da['url'][i]));
                    }
                    return Card(
                        child:ListTile(
                          title: Container(
                            alignment: Alignment.centerLeft,
                            child: Column(
                              children: <Widget>[
                                SizedBox(height: 5.0),
                                Container(alignment: Alignment.centerLeft,
                                  child: Row(
                                    children: [
                                      Text("Sumber Aduan: ", style: GoogleFonts.asap(fontWeight: FontWeight.bold)),
                                      Text(da['sumberAduan'], style: GoogleFonts.asap(fontWeight: FontWeight.bold)),
                                    ],
                                  ),
                                ),
                                SizedBox(height: 5.0),
                                Container(alignment: Alignment.centerLeft,
                                  child: Row(
                                    children: [
                                      Text("Nombor Aduan: ", style: GoogleFonts.lato(fontWeight: FontWeight.bold)),
                                      Text(da['noAduan'], style: GoogleFonts.lato(fontWeight: FontWeight.bold)),
                                    ],
                                  ),
                                ),
                                SizedBox(height: 5.0),
                                Container(alignment: Alignment.centerLeft,
                                  child: Row(
                                    children: [
                                      Text("Lokasi: ", style: GoogleFonts.lato(fontWeight: FontWeight.bold)),
                                      Text(da['kawasan'] + " " + da['naJalan'], style: GoogleFonts.lato(fontWeight: FontWeight.bold)),
                                    ],
                                  ),
                                ),
                                SizedBox(height: 5.0),
                                Container(alignment: Alignment.centerLeft,
                                  child: Row(
                                    children: [
                                      Text("Kategori: ", style: GoogleFonts.arimo(fontWeight: FontWeight.w500)),
                                      Text(da['kategori'], style: GoogleFonts.arimo(fontWeight: FontWeight.w500)),
                                    ],
                                  ),
                                ),
                                Column(
                                  children: [
                                    Container(
                                      margin: EdgeInsets.all(10.0),
                                      height: 200,
                                      decoration: BoxDecoration(
                                          color: Colors.white
                                      ),
                                      width: MediaQuery.of(context).size.width,
                                      child: Carousel(
                                        boxFit: BoxFit.cover,
                                        images: _listOfImages,
                                        autoplay: false,
                                        indicatorBgPadding: 5.0,
                                        dotPosition: DotPosition.bottomCenter,
                                        animationCurve: Curves.fastLinearToSlowEaseIn,
                                        animationDuration: Duration(milliseconds: 2000),
                                      ),
                                    )
                                  ],
                                )
                              ],
                            ),
                          ),
                          subtitle: Container(
                          child: Column(
                            children: [
                              SizedBox(height: 5.0),
                              Container(alignment: Alignment.centerLeft,
                                child: Row(
                                  children: [
                                    Text("Catatan: ", style: GoogleFonts.arimo(fontWeight: FontWeight.w500)),
                                    Text(da['comments'], style: GoogleFonts.arimo(fontWeight: FontWeight.w500)),
                                  ],
                                ),
                              ),
                            ],
                          ),
                        ),
                          onTap: () {Navigator.push(context, MaterialPageRoute(builder: (context) => EditTask(da:da)));}
                        )
                    );
                  });
               }
          }),
       )
    );
  }
}

这是 EditTask class，我需要显示用户 select 编辑的图像的当前索引。

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



class EditTask extends StatefulWidget {
 final DocumentSnapshot da;

  const EditTask({Key key, this.da}) : super(key: key);

  @override
  _EditTaskState createState() => _EditTaskState(da);
}

class _EditTaskState extends State<EditTask> {
  DocumentSnapshot da;
  _EditTaskState(DocumentSnapshot da){
    this.da = da;
  }
 TextEditingController _noAduan;
 TextEditingController _sumberAduan;
 TextEditingController _kategori;
  DateTime myDateTime = DateTime.now();
 @override
 void initState(){
   super.initState();
   _noAduan = TextEditingController(text: widget.da.data['noAduan']);
   _sumberAduan =TextEditingController(text: widget.da.data['sumberAduan']);
   _kategori = TextEditingController(text: widget.da.data['kategori']);
   myDateTime = (da.data['date']).toDate();
  _listOfImages = NetworkImage(da.data['url']) as List<NetworkImage>; // this line show the error 

}

  List <String> sumber = <String> ['Sistem Aduan MBPJ', 'Sistem Aduan Waze', 'Sistem Aduan Utiliti'];
  List <String> kate = <String> ['Segera', 'Pembaikan Biasa'];
  String kategori;
  String sumberAduan;
  List <NetworkImage> _listOfImages = <NetworkImage>[];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Kemaskini Aduan"),
          backgroundColor: Colors.redAccent,
        ),
    body: Container(
      padding: const EdgeInsets.all(16.0),
      child: Center(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.end,
            children: [
              SizedBox(height: 10.0),
              TextFormField(
                decoration:InputDecoration(
                    hintText: myDateTime.toString(),
                    border: OutlineInputBorder(
                        borderRadius: BorderRadius.circular(5))),
                onChanged: (value){
                  setState(() {
                    myDateTime = value as DateTime;
                    print(myDateTime);
                  });
                },
              ),
              SizedBox(height: 10.0),
              TextFormField(
                decoration:InputDecoration(
                  border: OutlineInputBorder(
                  borderRadius: BorderRadius.circular(5))),
                controller: _noAduan,
              ),
              SizedBox(height: 10.0),
              DropdownButtonFormField(
                hint:Text(widget.da.data['sumberAduan']),
                decoration: InputDecoration(
                    prefixIcon: Icon(Icons.perm_contact_calendar),
                    border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
                isExpanded: true,
                value: sumberAduan,
                onChanged: (newValue) {
                  setState(() {
                    sumberAduan = newValue;
                    _sumberAduan.text = sumberAduan;
                  });
                },
                items: sumber.map((sum){
                  return DropdownMenuItem(
                    value: sum,
                    child: new Text(sum),
                  );
                }).toList(),
              ),
              SizedBox(height: 10.0),
              DropdownButtonFormField(
                hint:Text(widget.da.data['kategori']),
                decoration: InputDecoration(
                    prefixIcon: Icon(Icons.perm_contact_calendar),
                    border: OutlineInputBorder(borderRadius: BorderRadius.circular(5))),
                isExpanded: true,
                value: kategori,
                onChanged: (newValue) {
                  setState(() {
                    kategori = newValue;
                    _kategori.text = kategori;
                  });
                },
                items: kate.map((ka){
                  return DropdownMenuItem(
                    value: ka,
                    child: new Text(ka),
                  );
                }).toList(),
              ),
              Container(
                margin: EdgeInsets.all(10.0),
                height: 200,
                decoration: BoxDecoration(
                    color: Colors.white
                ),
                width: MediaQuery.of(context).size.width,
                child: Carousel(
                  boxFit: BoxFit.cover,
                  autoplay: false,
                  //images: _listOfImages,
                  indicatorBgPadding: 5.0,
                  dotPosition: DotPosition.bottomCenter,
                  animationCurve: Curves.fastLinearToSlowEaseIn,
                  animationDuration: Duration(milliseconds: 2000),
                ),
              )
            ],
          ),
      ),
    )
    );
  }
}

the image that need to display for update image 当用户想要更新来自 ListOfTaskNotApprove

的信息时，这就是我想在 class EditTask 中显示图像的方式

错误显示“类型 'List' 不是类型 'String' 的子类型” 有人能帮我吗？因为我尝试了很多方法来解决这个问题，但对我来说没有用。

Answer 1

你正在从 Firebase 存储中获取 url 的列表，它们是 Strings 但你正在将这些字符串添加到 [= 类型的列表中20=]Network Image 这是错误的。由于字符串列表无法转换为网络图像列表。

有两种方法可以解决这个问题-

将您的列表类型更改为列表，然后在显示此图片的任何位置使用将数据列为网络图像的参数。
```
 List<String> urls=new List();
 //suppose list is not empty
 ....
 return NetworkImage(urls[i]);
 ....
```

在将 url 添加到您的列表时添加网络图像对象并在显示图像时直接使用列表项。

 List<NetworkImage> list=new List();
 list.add(NetworkImage('some url'));
 ....
 return list[i];
 ....

Answer 2

你说：

_listOfImages = NetworkImage(da.data['url']) as List<NetworkImage>; // this line show the error

是的，您不能将 NetworkImage 转换为 List<NetworkImage>。你的意思可能是：

_listOfImages = [ NetworkImage(da.data['url']) ] as List<NetworkImage>;

如何解决：type 'List<dynamic>' 不是 type 'String' 的子类型

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