不明白为什么我在使用 image_picker 时会出现这个错误

Question

我在这里得到的唯一错误是代码File selectedImage; 和错误状态“必须初始化不可为空的实例字段'selectedImage'。尝试添加初始化表达式，或初始化它的生成构造函数，或标记它'迟到'。

这是我的代码：

import 'dart:io';
import 'package:tennis_event_app/services/crud.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_storage/firebase_storage.dart';

import 'package:flutter/material.dart';
import 'package:image_picker/image_picker.dart';
import 'package:random_string/random_string.dart';

class CreateBlog extends StatefulWidget {
  @override
  _CreateBlogState createState() => _CreateBlogState();
}

class _CreateBlogState extends State<CreateBlog> {
  //
  File selectedImage;
  final picker = ImagePicker();

  bool isLoading = false;

  CrudMethods crudMethods = new CrudMethods();

  Future getImage() async {
    final pickedFile = await picker.getImage(source: ImageSource.gallery);

    setState(() {
      if (pickedFile != null) {
        selectedImage = File(pickedFile.path);
      } else {
        print('No image selected.');
      }
    });
  }

  Future<void> uploadBlog() async {
    if (selectedImage != null) {
      // upload the image

      setState(() {
        isLoading = true;
      });
      Reference firebaseStorageRef = FirebaseStorage.instance
          .ref()
          .child("blogImages")
          .child("${randomAlphaNumeric(9)}.jpg");

      final UploadTask task = firebaseStorageRef.putFile(selectedImage);

      var imageUrl;
      await task.whenComplete(() async {
        try {
          imageUrl = await firebaseStorageRef.getDownloadURL();
        } catch (onError) {
          print("Error");
        }

        print(imageUrl);
      });

      // print(downloadUrl);

      Map<String, dynamic> blogData = {
        "imgUrl": imageUrl,
        "author": authorTextEditingController.text,
        "title": titleTextEditingController.text,
        "desc": descTextEditingController.text
      };

      crudMethods.addData(blogData).then((value) {
        setState(() {
          isLoading = false;
        });
        Navigator.pop(context);
      });

      // upload the blog info
    }
  }

  //
  TextEditingController titleTextEditingController =
      new TextEditingController();
  TextEditingController descTextEditingController = new TextEditingController();
  TextEditingController authorTextEditingController =
      new TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Create Blog"),
        actions: [
          GestureDetector(
            onTap: () {
              uploadBlog();
            },
            child: Padding(
                padding: EdgeInsets.symmetric(horizontal: 16),
                child: Icon(Icons.file_upload)),
          )
        ],
      ),
      body: isLoading
          ? Container(
              child: Center(
              child: CircularProgressIndicator(),
            ))
          : SingleChildScrollView(
              child: Container(
                  margin: EdgeInsets.symmetric(horizontal: 16),
                  child: Column(
                    children: [
                      GestureDetector(
                        onTap: () {
                          getImage();
                        },
                        child: selectedImage != null
                            ? Container(
                                height: 150,
                                margin: EdgeInsets.symmetric(vertical: 24),
                                width: MediaQuery.of(context).size.width,
                                child: ClipRRect(
                                  borderRadius:
                                      BorderRadius.all(Radius.circular(8)),
                                  child: Image.file(
                                    selectedImage,
                                    fit: BoxFit.cover,
                                  ),
                                ),
                              )
                            : Container(
                                height: 150,
                                decoration: BoxDecoration(
                                    color: Colors.grey,
                                    borderRadius:
                                        BorderRadius.all(Radius.circular(8))),
                                margin: EdgeInsets.symmetric(vertical: 24),
                                width: MediaQuery.of(context).size.width,
                                child: Icon(
                                  Icons.camera_alt,
                                  color: Colors.white,
                                ),
                              ),
                      ),
                      TextField(
                        controller: titleTextEditingController,
                        decoration: InputDecoration(hintText: "enter title"),
                      ),
                      TextField(
                        controller: descTextEditingController,
                        decoration: InputDecoration(hintText: "enter desc"),
                      ),
                      TextField(
                        controller: authorTextEditingController,
                        decoration:
                            InputDecoration(hintText: "enter author name"),
                      ),
                    ],
                  )),
            ),
    );
  }
}

我也收到两个警告，但不确定这里是否真的存在问题。这是第 37 行和第 118 行的警告，“操作数不能为空，因此条件始终为真。”

任何帮助将不胜感激，我已经坚持了两天！

Answer 1

您似乎正在使用空安全性。所以问题是File selectedImage 被标记为不可为空，但你没有在构造函数中初始化它。尝试将其替换为 File? selectedImage 或 late File selectedImage。

在第 37 和 118 行删除 !因为没有必要。

我建议您阅读https://flutter.dev/docs/null-safety，因为它的解释非常详细。