如何播放Firebase视频的列表数组：在我的情况下，我尝试了很多更改，但出现此错误

如何解决如何播放Firebase视频的列表数组：在我的情况下，我尝试了很多更改，但出现此错误

这里有我的两个Dart文件，我从firestore中检索了我的视频，但是在这种情况下，我制作了视频数组并尝试对其进行检索，但是如果我使用字符串而不是数组来执行，它会给我一个错误。很好，但是在我的项目中，我需要数组，所以请帮我指点一下。

我的云存储库看起来像是：collection（Course）=> autoid => doucuments（video array）=>（[[0] url [1] url2）

这是我的2个Dart文件，请更正我的代码，在这种情况下，当我运行此程序时出现了错误：

错误：列表不是'string'类型的子类型。

code:main.dart and chewie_list_item.dart

     main.dart:It is for retrieve data

   import 'chewie_list_item.dart';
        import 'package:Flutter/foundation.dart';
        import 'package:Flutter/material.dart';
        import 'package:cloud_firestore/cloud_firestore.dart';`enter code here`
        import 'package:video_player/video_player.dart';
        
        void main() {
          FlutterError.onError = (FlutterErrorDetails details) {
            FlutterError.dumpErrorToConsole(details);
            if (kReleaseMode) exit(1);
          };
        
          runApp(MaterialApp(
            home: CourseApp(),));
        }
        
        class CourseApp extends StatelessWidget {
          // This widget is the root of your application.
          @override
          Widget build(BuildContext context) {
            return Scaffold(
                appBar: AppBar(
                  title: Text("Flutter Demo"),),body: StreamBuilder(
                  stream: Firestore.instance.collection("courses").snapshots(),builder: (context,snapshot) {
                    return ListView.builder(
                      itemCount: snapshot.data.documents.length,itemBuilder: (context,index) {
                        DocumentSnapshot courses = snapshot.data.documents[index];
                        return (ChewieListItem(
                          videoPlayerController: VideoPlayerController.network(
                              courses['video'] ?? 'default'),));
                      },);
                  },));
          }
        }
        
        [code 2: chewie_list_item.dart]: It for chewie video player. 
        
        import 'package:chewie/chewie.dart';
        import 'package:Flutter/material.dart';
        import 'package:video_player/video_player.dart';
        
        class ChewieListItem extends StatefulWidget {
          // This will contain the URL/asset path which we want to play
          final VideoPlayerController videoPlayerController;
          final bool looping;
        
          ChewieListItem({
            @required this.videoPlayerController,this.looping,Key key,}) : super(key: key);
        
          @override
          _ChewieListItemState createState() => _ChewieListItemState();
        }
        
        class _ChewieListItemState extends State<ChewieListItem> {
          ChewieController _chewieController;
        
          @override
          void initState() {
            super.initState();
            // Wrapper on top of the videoPlayerController
            _chewieController = ChewieController(
              videoPlayerController: widget.videoPlayerController,aspectRatio: 16 / 9,// Prepare the video to be played and display the first frame
              autoInitialize: true,looping: widget.looping,// Errors can occur for example when trying to play a video
              // from a non-existent URL
              errorBuilder: (context,errorMessage) {
                return Center(
                  child: Text(
                    errorMessage,style: TextStyle(color: Colors.white),);
              },);
          }
        
          @override
          Widget build(BuildContext context) {
            return Padding(
              padding: const EdgeInsets.all(8.0),child: Chewie(
                controller: _chewieController,);
          }
        
          @override
          void dispose() {
            super.dispose();
            // IMPORTANT to dispose of all the used resources
            widget.videoPlayerController.dispose();
            _chewieController.dispose();
          }
        }
    
    

所以主要我不知道要从我的Firebase检索此视频数组，请提供正确的代码。