Error: The argument type 'String?' can't be assigned to the parameter type 'Stri-CodePudding

I am working on ChatApp trying to save and upload images but I get errors like this Does anyone know the cause of this ? im getting theese type of error i cant fnd any solutons for these..

import 'dart:io';

//Packages
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_storage/firebase_storage.dart';
import 'package:file_picker/file_picker.dart';

const String USER_COLLECTION = "Users";

class CloudStorageService {
  final FirebaseStorage _storage = FirebaseStorage.instance;

  CloudStorageService();

  Future<String?> saveUserImageToStorage(
      String _uid, PlatformFile _file) async {
    try {
      Reference _ref =
          _storage.ref().child('images/users/$_uid/profile.${_file.extension}');
      UploadTask _task = _ref.putFile(
        [enter image description here][1]File(_file.path),
      );
      return await _task.then(
        (_result) => _result.ref.getDownloadURL(),
      );
    } catch (e) {
      print(e);
    }
  }

  Future<String?> saveChatImageToStorage(
      String _chatID, String _userID, PlatformFile _file) async {
    try {
      Reference _ref = _storage.ref().child(
          'images/chats/$_chatID/${_userID}_${Timestamp.now().millisecondsSinceEpoch}.${_file.extension}');
      UploadTask _task = _ref.putFile(
        File(_file.path), ----------------> Here is the error
      );
      return await _task.then(
        (_result) => _result.ref.getDownloadURL(),
      );
    } catch (e) {
      print(e);
    }
  }
}

CodePudding user response：

Use the ! operator to convert the string to a non-nullable type

File(_file.path!)

CodePudding user response：

String? means it may have value, or it may have null value, but String means it have an appropriate value String type. You can add ! to the last of the data type to sure it's not null.

For example:

String? name = "Jack";
String name2 = name!;

CodePudding user response：

The Dart programming language supports null safety. It means that in Dart nullable and non-nullable types is completely different. E.g.

bool b; // can be true or false
bool? nb; // can be true, false or null, `?` is explicit declaration, that type is nullable

So, String? and String is completely different types. First can be string or null, second can only be a string. And you need to check for null in your case.