Implement In-App Download Feature In Flutter App Easily.

It’s not hard as it seems.

To implement in-app downloads in a Flutter app, you need to use libraries that can handle downloading files and managing states effectively. A common choice is the dio package for making HTTP requests, along with the path_provider package to save the downloaded file in the device’s local storage.

Here’s how you can implement in-app downloads in Flutter:

Step 1: Add Dependencies

Update your pubspec.yaml file to include the required packages:

dependencies:
  dio: ^5.0.0
  path_provider: ^2.0.14
  permission_handler: ^11.0.0

Run flutter pub get to install the dependencies.

Step 2: Request Permissions

Before downloading a file, you must ensure the app has the required permissions to write files to the device’s storage.

import 'package:permission_handler/permission_handler.dart';
Future<void> requestStoragePermission() async {
  if (await Permission.storage.request().isDenied) {
    // Show a message if permission is denied
    print('Storage permission denied');
  }
}

Step 3: Implement the Download Functionality

Use the dio package to handle the file download.

import 'dart:io';
import 'package:dio/dio.dart';
import 'package:path_provider/path_provider.dart';
class Downloader {
  final Dio _dio = Dio();
  Future<void> downloadFile(String url, String fileName) async {
    try {
      // Get the directory for saving the file
      final dir = await getApplicationDocumentsDirectory();
      // Build the file path
      final filePath = "${dir.path}/$fileName";
      // Start the download
      await _dio.download(
        url,
        filePath,
        onReceiveProgress: (received, total) {
          if (total != -1) {
            // Show the download progress (in percentage)
            print("Download Progress: ${(received / total * 100).toStringAsFixed(0)}%");
          }
        },
      );
      print("File downloaded successfully: $filePath");
    } catch (e) {
      print("Download failed: $e");
    }
  }
}

Step 4: Create a UI for the Download

Here’s an example of a simple UI to trigger the download:

import 'package:flutter/material.dart';
import 'downloader.dart';
class DownloadScreen extends StatelessWidget {
  final String fileUrl = "https://example.com/sample.pdf";
  final String fileName = "sample.pdf";
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("In-App Download Example"),
      ),
      body: Center(
        child: ElevatedButton(
          onPressed: () async {
            final downloader = Downloader();
            await downloader.downloadFile(fileUrl, fileName);
            ScaffoldMessenger.of(context).showSnackBar(
              SnackBar(content: Text("Download started!")),
            );
          },
          child: Text("Download File"),
        ),
      ),
    );
  }
}

Step 5: Handle Edge Cases

To make your download process robust:

1. Network Errors: Wrap the download logic in a try-catch block to handle timeouts or connectivity issues.
2. File Overwriting: Check if the file already exists and handle appropriately.
3. User Feedback: Show a loading spinner or progress bar during the download process.

Step 6: Add Progress Indicators (Optional)

You can enhance the UI by displaying the progress using a progress bar.

import 'package:flutter/material.dart';
import 'downloader.dart';
class DownloadScreenWithProgress extends StatefulWidget {
  @override
  _DownloadScreenWithProgressState createState() => _DownloadScreenWithProgressState();
}
class _DownloadScreenWithProgressState extends State<DownloadScreenWithProgress> {
  double _progress = 0.0;
  Future<void> startDownload() async {
    final downloader = Downloader();
    await downloader._dio.download(
      "https://example.com/sample.pdf",
      "${(await getApplicationDocumentsDirectory()).path}/sample.pdf",
      onReceiveProgress: (received, total) {
        if (total != -1) {
          setState(() {
            _progress = received / total;
          });
        }
      },
    );
    ScaffoldMessenger.of(context).showSnackBar(
      SnackBar(content: Text("Download complete!")),
    );
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Download with Progress"),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            LinearProgressIndicator(value: _progress),
            SizedBox(height: 20),
            ElevatedButton(
              onPressed: startDownload,
              child: Text("Start Download"),
            ),
          ],
        ),
      ),
    );
  }
}

Key Considerations

1. Permission Management: Use permission_handler to request permissions dynamically.
2. Offline Storage: Save files to device directories using path_provider.
3. Background Downloads: For downloads that need to continue when the app is in the background, consider using native integrations (e.g., workmanager or platform channels).

Thank You, Hope You Enjoyed.