当我尝试删除数据库中的文件（之前已删除）时，它显示以下内容：“没有为类型”Reference“定义方法”exists“。“
我认为这是因为当我发送调用路径时，它没有找到任何文件，这就是为什么它提到我它不存在。
没有为类型“Reference”定义方法“exists”。
请尝试将名称更正为现有方法的名称，或定义名为“exists”的方法

String ref = _selectedRef!;

    if (!ref.startsWith("/")) {

      ref = "/" + ref;

    }

    ref = ref.substring(0, ref.lastIndexOf("/") + 1) + ".pdf";

我的问题是：

// validate if the reference exists

    **bool exists = await FirebaseStorage.instance.ref(ref).exists();**

这里我们需要等待是否存在引用：

if (exists) {

      await FirebaseStorage.instance.ref(ref).delete();

      await FirebaseFirestore.instance

          .collection("file")

          .where("ref", isEqualTo: _selectedRef)

          .get()

          .then((snapshot) {

        snapshot.docs.first.reference.delete();

      });

      setState(() {

        _selectedRef = null;

      });

    } else {

      ScaffoldMessenger.of(context).showSnackBar(

          SnackBar(content: Text("El archivo seleccionado no existe")));

    }

  }

这是我的完整代码：

import 'dart:io';

import 'dart:math';

import 'package:cloud_firestore/cloud_firestore.dart';

import 'package:file_picker/file_picker.dart';

import 'package:fimprac/screen_acercade.dart';

import 'package:fimprac/screen_home.dart';

import 'package:fimprac/main.dart';

import 'package:firebase_core/firebase_core.dart';

import 'package:firebase_storage/firebase_storage.dart';

import 'package:flutter/material.dart';

import 'package:flutter/src/material/navigation_drawer.dart';

import 'package:fimprac/menu.dart';

import 'package:syncfusion_flutter_pdfviewer/pdfviewer.dart';

main() async {

  WidgetsFlutterBinding.ensureInitialized();

  await Firebase.initializeApp();

  runApp(MaterialApp(

    debugShowCheckedModeBanner: false,

    home: perfilSC(),

  ));

}

class perfilSC extends StatefulWidget {

  const perfilSC({super.key});

  @override

  State<perfilSC> createState() => _perfilSCState();

}

class _perfilSCState extends State<perfilSC> {

  String?

      _selectedRef; //agrega una variable para almacenar la referencia del archivo seleccionado

  String url = "";

  int? number;

  late QueryDocumentSnapshot selectedSnapshot;

  uploadDataToFirebase() async {

    //generate random number

    number = Random().nextInt(10);

    //pick pdf file

    FilePickerResult? result = await FilePicker.platform.pickFiles();

    File pick = File(result!.files.single.path.toString());

    var file = pick.readAsBytesSync();

    String name = DateTime.now().millisecondsSinceEpoch.toString();

    //uploading file to firebase

    var pdfFile = FirebaseStorage.instance.ref().child(name).child("/.pdf");

    UploadTask task = pdfFile.putData(file);

    TaskSnapshot snapshot = await task;

    url = await snapshot.ref.getDownloadURL();

    String ref = name + "/.pdf"; // establece la referencia del archivo

    //upload to url to cloud firebase

    await FirebaseFirestore.instance.collection("file").doc().set({

      'fileUrl': url,

      'num': "CV#" + number.toString(),

      'ref': name + "/.pdf" // agrega la referencia del archivo

    });

  }

  Future<void> deleteFile() async {

    if (_selectedRef != null) {

      showDialog(

        context: context,

        builder: (BuildContext context) {

          return AlertDialog(

            title: Text('¿Estás seguro que quieres eliminar el archivo?'),

            actions: <Widget>[

              TextButton(

                child: Text('Cancelar'),

                onPressed: () {

                  Navigator.of(context).pop();

                },

              ),

              TextButton(

                child: Text('Eliminar'),

                onPressed: () async {

                  await deleteFirebaseData();

                  Navigator.of(context).pop();

                  ScaffoldMessenger.of(context).showSnackBar(

                      SnackBar(content: Text("Archivo eliminado")));

                },

              ),

            ],

          );

        },

      );

    } else {

      ScaffoldMessenger.of(context).showSnackBar(

          SnackBar(content: Text("Selecciona un archivo para eliminar")));

    }

  }

  Future<void> deleteFirebaseData() async {

    if (_selectedRef == null) {

      ScaffoldMessenger.of(context).showSnackBar(

          SnackBar(content: Text("Selecciona un archivo para eliminar")));

      return;

    }

    // construir la ruta completa de la referencia del archivo

    String ref = _selectedRef!;

    if (!ref.startsWith("/")) {

      ref = "/" + ref;

    }

    ref = ref.substring(0, ref.lastIndexOf("/") + 1) + ".pdf";

    // validar si la referencia existe

    bool exists = await FirebaseStorage.instance.ref(ref).exists();

    if (exists) {

      await FirebaseStorage.instance.ref(ref).delete();

      await FirebaseFirestore.instance

          .collection("file")

          .where("ref", isEqualTo: _selectedRef)

          .get()

          .then((snapshot) {

        snapshot.docs.first.reference.delete();

      });

      setState(() {

        _selectedRef = null;

      });

    } else {

      ScaffoldMessenger.of(context).showSnackBar(

          SnackBar(content: Text("El archivo seleccionado no existe")));

    }

  }

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      drawer: const NavigationDrawerMenu(),

      appBar: AppBar(

        backgroundColor: Colors.green,

        title: Text('PDF'),

      ),

      body: StreamBuilder(

          stream: FirebaseFirestore.instance.collection("file").snapshots(),

          builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {

            if (snapshot.hasData) {

              return ListView.builder(

                  itemCount: snapshot.data!.docs.length,

                  itemBuilder: (context, i) {

                    QueryDocumentSnapshot x = snapshot.data!.docs[i];

                    return InkWell(

                      onTap: () {

                        setState(() {

                          selectedSnapshot = x; // asignar valor a la variable

                        });

                        Navigator.push(

                            context,

                            MaterialPageRoute(

                                builder: (context) => View(

                                      url: x['fileUrl'],

                                    )));

                      },

                      child: Container(

                        margin: EdgeInsets.symmetric(vertical: 10),

                        child: Text(x["num"]),

                      ),

                    );

                  });

            }

            return Center(

              child: CircularProgressIndicator(),

            );

          }),

      floatingActionButton: Row(

        children: [

          FloatingActionButton(

            heroTag: "btn1",

            onPressed: () {

              setState(() {

                _selectedRef = selectedSnapshot[

                    'ref']; //almacena la referencia del archivo seleccionado

              });

              deleteFile();

            },

            child: Icon(Icons.delete),

          ),

          SizedBox(width: 10),

          Expanded(

            child: FloatingActionButton(

              heroTag: "btn2",

              onPressed: () => uploadDataToFirebase(),

              child: Icon(Icons.add),

            ),

          ),

        ],

      ),

    );

  }

}

class View extends StatelessWidget {

  PdfViewerController? _pdfViewerController;

  final url;

  View({this.url});

  @override

  Widget build(BuildContext context) {

    return Scaffold(

      appBar: AppBar(

        title: Text("PDF VIEW"),

      ),

      body: SfPdfViewer.network(

        url,

        controller: _pdfViewerController,

      ),

    );

  }

}