How do I upload a file to Google Drive using Flutter?

Its easy but you have to go through a series of Steps to complete it.

1. Enable Google Drive API

click on the link to google console : https://console.developers.google.com/apis/library?project=diary-app-339509

• Create a new project and enable Drive API on the project.
• Create an OAuth client Id for android and IOS
• You will have to fill a lot of details to create it , read through the page and fill it
• copy Client ID for future use

create project and enable API

Create OAuth client id

form to fill to make OAuth client id

2. Make project available for external use .

for testing add test user email address

Now comes the coding part on flutter

3. Add the following packages to pubspec.yaml

  googleapis: ^7.0.0
  googleapis_auth: ^1.3.0
  flutter_secure_storage: ^5.0.2
  url_launcher: ^6.0.0-nullsafety

4. Get authentication from google and store the Auth details for future auths

Use the following class for storing Auth Details

import 'package:flutter_secure_storage/flutter_secure_storage.dart';
import 'package:googleapis_auth/auth_io.dart';

class SecureStorage {
  final storage = FlutterSecureStorage();

  //Save Credentials
  Future saveCredentials(AccessToken token, String refreshToken) async {
    print(token.expiry.toIso8601String());
    await storage.write(key: "type", value: token.type);
    await storage.write(key: "data", value: token.data);
    await storage.write(key: "expiry", value: token.expiry.toString());
    await storage.write(key: "refreshToken", value: refreshToken);
  }

  //Get Saved Credentials
  Future<Map<String, dynamic>?> getCredentials() async {
    var result = await storage.readAll();
    if (result.isEmpty) return null;
    return result;
  }

  //Clear Saved Credentials
  Future clear() {
    return storage.deleteAll();
  }
}

5.Finally use this class for saving your file to Drive

import 'dart:io';
import 'package:googleapis/drive/v3.dart' as ga;
import 'package:googleapis_auth/auth_io.dart';
import 'package:http/http.dart' as http;
import 'package:path/path.dart' as p;
import 'package:personal_diary/app/utils/secure_storage.dart';
import 'package:url_launcher/url_launcher.dart';

const _clientId = "YOUR CLIENT ID FROM GOOGLE CONSOLE";
const _scopes = ['https://www.googleapis.com/auth/drive.file'];

class GoogleDrive {
  final storage = SecureStorage();
  //Get Authenticated Http Client
  Future<http.Client> getHttpClient() async {
    //Get Credentials
    var credentials = await storage.getCredentials();
    if (credentials == null) {
      //Needs user authentication
      var authClient = await clientViaUserConsent(
          ClientId(_clientId),_scopes, (url) {
        //Open Url in Browser
        launch(url);
      });
      //Save Credentials
      await storage.saveCredentials(authClient.credentials.accessToken,
          authClient.credentials.refreshToken!);
      return authClient;
    } else {
      print(credentials["expiry"]);
      //Already authenticated
      return authenticatedClient(
          http.Client(),
          AccessCredentials(
              AccessToken(credentials["type"], credentials["data"],
                  DateTime.tryParse(credentials["expiry"])!),
              credentials["refreshToken"],
              _scopes));
    }
  }

// check if the directory forlder is already available in drive , if available return its id
// if not available create a folder in drive and return id
//   if not able to create id then it means user authetication has failed
  Future<String?> _getFolderId(ga.DriveApi driveApi) async {
    final mimeType = "application/vnd.google-apps.folder";
    String folderName = "personalDiaryBackup";

    try {
      final found = await driveApi.files.list(
        q: "mimeType = '$mimeType' and name = '$folderName'",
        $fields: "files(id, name)",
      );
      final files = found.files;
      if (files == null) {
        print("Sign-in first Error");
        return null;
      }

      // The folder already exists
      if (files.isNotEmpty) {
        return files.first.id;
      }

      // Create a folder
      ga.File folder = ga.File();
      folder.name = folderName;
      folder.mimeType = mimeType;
      final folderCreation = await driveApi.files.create(folder);
      print("Folder ID: ${folderCreation.id}");

      return folderCreation.id;
    } catch (e) {
      print(e);
      return null;
    }
  }

  
  uploadFileToGoogleDrive(File file) async {
    var client = await getHttpClient();
    var drive = ga.DriveApi(client);
    String? folderId =  await _getFolderId(drive);
    if(folderId == null){
      print("Sign-in first Error");
    }else {
      ga.File fileToUpload = ga.File();
      fileToUpload.parents = [folderId];
      fileToUpload.name = p.basename(file.absolute.path);
      var response = await drive.files.create(
        fileToUpload,
        uploadMedia: ga.Media(file.openRead(), file.lengthSync()),
      );
      print(response);
    }

  }




}

Turns out in addition to enabling the API and creating the service account, I ALSO needed to share the folder I wanted to upload to with the service account email address from the JSON.