<key>NSAllowsArbitraryLoads</key>
<true/>
<key>LSSupportsOpeningDocumentsInPlace</key>
<true/>
<key>UIFileSharingEnabled</key>
<true/>

if #available(iOS 10.0, *) {
  UNUserNotificationCenter.current().delegate = self as? UNUserNotificationCenterDelegate
}

if (@available(iOS 10.0, *)) {
  [UNUserNotificationCenter currentNotificationCenter].delegate = (id<UNUserNotificationCenterDelegate>) self;
}

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  String _progress = "-";

  Future<void> _download() async {
    // download
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Download progress:',
            ),
            Text(
              '$_progress',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _download,
        tooltip: 'Download',
        child: Icon(Icons.file_download),
      ),
    );
  }
}

final String _fileUrl = "http://lot.services/blog/files/DSCF0277.jpg";
final String _fileName = "DSCF0277.jpg";

  Future<Directory> _getDownloadDirectory() async {
    if (Platform.isAndroid) {
      return await DownloadsPathProvider.downloadsDirectory;
    }

    // in this example we are using only Android and iOS so I can assume
    // that you are not trying it for other platforms and the if statement
    // for iOS is unnecessary
  
    // iOS directory visible to user
    return await getApplicationDocumentsDirectory();
  }

  Future<bool> _requestPermissions() async {
    var permission = await PermissionHandler().checkPermissionStatus(PermissionGroup.storage);

    if (permission != PermissionStatus.granted) {
      await PermissionHandler().requestPermissions([PermissionGroup.storage]);
      permission = await PermissionHandler().checkPermissionStatus(PermissionGroup.storage);
    }

    return permission == PermissionStatus.granted;
  }

  Future<void> _download() async {
    final dir = await _getDownloadDirectory();
    final isPermissionStatusGranted = await _requestPermissions();

    if (isPermissionStatusGranted) {
      final savePath = path.join(dir.path, _fileName);
      await _startDownload(savePath);
    } else {
      // handle the scenario when user declines the permissions
    }
  }

import 'package:path/path.dart' as path;

Step 8. Download process

Finally, it’s time to download our file. Create an instance of Dio and add _startDownload() method which will download a file from the provided url to “save path”.

  final Dio _dio = Dio();

  Future<void> _startDownload(String savePath) async {
    final response = await _dio.download(
      _fileUrl,
      savePath
    );
  }

To update download progress, we need to add one more method in which we will calculate the percentage download status.

Simple as that.

  void _onReceiveProgress(int received, int total) {
    if (total != -1) {
      setState(() {
        _progress = (received / total * 100).toStringAsFixed(0) + "%";
      });
    }
  }

Now, to enable the process of calculating the progress, we have to pass our method as a parameter to Dio’s download function.

  final response = await _dio.download(
    _fileUrl,
    savePath,
    onReceiveProgress: _onReceiveProgress
  );

Build and run the example and you should already be able to download the file and see the progress updated as shown below.

Step 9. Local notifications initialization

Create a new instance of the flutter_local_notifications plugin and initialize it.

FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin;

Initialisation should only be done once and the place where this can be done is in the main function, or alternatively within the first shown page of your app. Override initState and initialize it.

  @override
  void initState() {
    super.initState();

    flutterLocalNotificationsPlugin = FlutterLocalNotificationsPlugin();
    final android = AndroidInitializationSettings('@mipmap/ic_launcher');
    final iOS = IOSInitializationSettings();
    final initSettings = InitializationSettings(android, iOS);

    flutterLocalNotificationsPlugin.initialize(initSettings, onSelectNotification: _onSelectNotification);
  }

For now, add also an empty onSelectNotification method.

  Future<void> _onSelectNotification(String json) async {
    // todo: handling clicked notification
  }

Step 10. Calling _showNotification method on downloads finish

After the download is completed, we need to show the notification whether it has succeeded or not. Modify our _startDownload method.

  Future<void> _startDownload(String savePath) async {
    Map<String, dynamic> result = {
      'isSuccess': false,
      'filePath': null,
      'error': null,
    };

    try {
      final response = await _dio.download(
        _fileUrl,
        savePath,
        onReceiveProgress: _onReceiveProgress
      );
      result['isSuccess'] = response.statusCode == 200;
      result['filePath'] = savePath;
    } catch (ex) {
      result['error'] = ex.toString();
    } finally {
      await _showNotification(result);
    }
  }

We have added simple Map with three values to determine if a download is completed successfully and to store a file path or error message. The logic is also closed within try catch finally clause which finally calls _showNotification.

Step 11. Showing local notification

Add _showNotification method. In this method we will call show function to show simple notification.

  Future<void> _showNotification(Map<String, dynamic> downloadStatus) async {
    final android = AndroidNotificationDetails(
      'channel id',
      'channel name',
      'channel description',
      priority: Priority.High,
      importance: Importance.Max
    );
    final iOS = IOSNotificationDetails();
    final platform = NotificationDetails(android, iOS);
    final json = jsonEncode(downloadStatus);
    final isSuccess = downloadStatus['isSuccess'];

    await flutterLocalNotificationsPlugin.show(
      0, // notification id
      isSuccess ? 'Success' : 'Failure',
      isSuccess ? 'File has been downloaded successfully!' : 'There was an error while downloading the file.',
      platform,
      payload: json
    );
  }

Except the basic configuration needed to show the notification I have also encoded our Map to JSON and passed it to a payload parameter. The payload String will be used in the method fired when we tap the notification.

Step 12. Handling notification tap

The last thing we have to do is to fulfill our empty _onSelectNotification method. Here we will just decode our encoded Map to JSON String and open downloaded file if the download succeeded or show dialog with an error message.

  Future<void> _onSelectNotification(String json) async {
    final obj = jsonDecode(json);

    if (obj['isSuccess']) {
      OpenFile.open(obj['filePath']);
    } else {
      showDialog(
        context: context,
        builder: (_) => AlertDialog(
          title: Text('Error'),
          content: Text('${obj['error']}'),
        ),
      );
    }
  }

That’s it!

You can find the full example in my GitHub repository.