Reducing the Size of Flutter Apps

In the world of mobile app development, size matters. Large app sizes can deter users from downloading your Flutter app due to storage constraints, data costs, and perceived performance issues. Optimizing the size of your Flutter application is crucial for improving user experience, increasing install rates, and enhancing overall performance. Here’s a comprehensive guide on how to effectively reduce the size of your Flutter apps.

Why is App Size Important?

• User Adoption: Smaller apps are more likely to be downloaded, especially in regions with limited bandwidth or expensive data plans.
• Uninstall Rates: Users are more likely to uninstall large apps to free up storage space.
• App Store Ranking: App size can impact your app’s ranking in app stores.
• Download and Installation Time: Smaller apps download and install faster, providing a better user experience.
• Storage Space: Reduced app size saves storage space on users’ devices.

Tools for Analyzing App Size

Before diving into optimization techniques, it’s essential to understand what’s contributing to your app’s size. Flutter provides tools to analyze your app’s build output.

Flutter Analyze Size

The flutter analyze-size command provides insights into the size of your app’s Dart code.

flutter analyze-size --android-build-output build/app/outputs/apk/release/app-release.apk

This command generates a detailed breakdown of the size contributions from various parts of your Dart code.

Android APK Analyzer

For Android apps, use the Android Studio APK Analyzer to inspect the contents of your APK.

• Open Android Studio.
• Go to Build > Analyze APK.
• Select your APK file.

The APK Analyzer helps identify the size of various components like resources, native libraries, and DEX files.

iOS App Thinning Report

For iOS apps, Apple’s App Thinning technology ensures that only the resources needed for a particular device are downloaded. After submitting your app to TestFlight or the App Store, you can download a thinning report from App Store Connect.

Techniques to Reduce Flutter App Size

Now, let’s explore effective strategies to minimize your Flutter app’s size.

1. Enable Tree Shaking

Tree shaking is a process where the Dart compiler eliminates unused code from your application. Flutter automatically performs tree shaking during release builds, but it’s essential to ensure it’s working effectively.

• Avoid Importing Entire Libraries: Instead of importing an entire library, import only the specific parts you need.

// Bad
import 'package:flutter/material.dart';

// Good
import 'package:flutter/material.dart' show Scaffold, AppBar, Text, Center;

2. Compress Images

Images are often a significant contributor to app size. Compress images without losing noticeable quality to reduce their file size.

• Use Optimized Image Formats: Prefer using formats like WebP for Android and HEIF for iOS, which offer better compression than JPEG or PNG.
• Tools for Image Compression: Use tools like TinyPNG, ImageOptim, or online services to compress images.
• Flutter Package: Use the flutter_image_compress package to compress images directly in your Flutter code.

import 'dart:io';
import 'package:flutter_image_compress/flutter_image_compress.dart';
import 'package:path_provider/path_provider.dart' as path_provider;

Future<File?> compressImage(File image) async {
  final tempDir = await path_provider.getTemporaryDirectory();
  final tempPath = tempDir.path;
  final targetPath = '$tempPath/${image.uri}compressed.jpg';

  var result = await FlutterImageCompress.compressAndGetFile(
    image.absolute.path,
    targetPath,
    quality: 88, // Adjust quality as needed
  );

  return result;
}

3. Optimize Assets

Beyond images, other assets can also contribute to app size. Optimize these assets to minimize their footprint.

• Remove Unused Assets: Delete any assets that are no longer used in your application.
• Use Vector Graphics: Prefer using vector graphics (SVGs) over raster images for icons and simple graphics. Vector graphics scale without losing quality and are typically smaller in size.
• Optimize Audio Files: Compress audio files and use appropriate formats.

dependencies:
  flutter_svg: ^2.0.0

4. Minify Dart Code

Minification removes unnecessary characters from your code, such as whitespace and comments, reducing the file size.

• Flutter Release Builds: Flutter automatically minifies code during release builds. Ensure you are building in release mode:

flutter build apk --split-per-abi --release

5. Use Code Obfuscation

Obfuscation renames classes, methods, and variables to make the code harder to reverse engineer. Although it doesn’t directly reduce app size, it can help protect your code.

• Enable Obfuscation: Add the --obfuscate flag to your build command:

flutter build apk --split-per-abi --release --obfuscate

6. Enable Code Splitting (Deferred Components)

Code splitting, or deferred components, allows you to split your application into separate components that can be downloaded on demand. This reduces the initial app size.

• Deferred Loading: Use deferred loading to load features only when they are needed.

import 'package:deferred_library/deferred_library.dart' deferred as my_feature;

Future<void> loadMyFeature() async {
  await my_feature.loadLibrary();
  my_feature.myFunction();
}

7. Remove Unused Dependencies

Evaluate your project dependencies and remove any packages that are no longer in use.

• Check pubspec.yaml: Review your pubspec.yaml file and remove unused dependencies.
• Run flutter pub get: After removing dependencies, run flutter pub get to update your project.

8. Use ProGuard (Android) or Link-Time Optimization (iOS)

ProGuard (Android) and Link-Time Optimization (LTO) (iOS) remove unused code during the build process.

• Android ProGuard: Enabled by default in release builds.
• iOS LTO: Enabled by default in release builds.

9. Use APK Splits (Android) and App Thinning (iOS)

APK splits (Android) and App Thinning (iOS) allow you to generate optimized APKs/IPAs for different device architectures and screen densities.

• APK Splits: Use the --split-per-abi flag to create separate APKs for each ABI:

flutter build apk --split-per-abi --release

• App Thinning: Automatically handled by Apple when you submit your app to the App Store.

10. Minimize Native Code Usage

If your Flutter app incorporates native code (e.g., Kotlin/Java for Android, Swift/Objective-C for iOS), ensure it’s optimized.

• Optimize Native Libraries: Reduce the size of native libraries and remove any unused native code.
• Review Dependencies: Minimize the number of native dependencies.

Example: Comprehensive Optimization Checklist

Here’s a comprehensive checklist you can follow to optimize your Flutter app:

1. Enable Tree Shaking: Use explicit imports.
2. Compress Images: Use optimized formats and compression tools.
3. Optimize Assets: Remove unused assets and use vector graphics.
4. Minify Dart Code: Build in release mode.
5. Use Code Obfuscation: Protect your code.
6. Enable Code Splitting: Use deferred components.
7. Remove Unused Dependencies: Review and clean up pubspec.yaml.
8. Use ProGuard (Android) or LTO (iOS): Let the build tools optimize.
9. Use APK Splits (Android) and App Thinning (iOS): Optimize for different devices.
10. Minimize Native Code Usage: Optimize native libraries.
11. Analyze App Size: Use flutter analyze-size and platform-specific tools.

Conclusion

Reducing the size of your Flutter app is a multifaceted task that requires attention to detail and the application of various optimization techniques. By following the strategies outlined in this guide, you can significantly reduce your app’s size, leading to improved user experience, higher install rates, and better overall performance. Always analyze your app’s size after each optimization step to measure the impact and identify further areas for improvement.