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Mastering App Size in Flutter: A Comprehensive Guide to Optimize Your Application

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Nidhi Sorathiya

August 25, 2023

Nidhi Sorathiya

August 25, 2023

Hello, Flutter enthusiasts! Are you worried about your Flutter app size getting out of control? If so, then you're in the right place. In this article, we'll walk through different aspects of app size in Flutter. We'll start by shedding some light on the importance of managing your app size and what role it plays in the overall user experience.

Understanding App Size in Flutter

The term 'app size' might seem simple at first glance, but it's a multifaceted concept in the context of Flutter application development. It's not just about how much space your app takes up on a user's device; it's about the impact on download time, the required storage, the effectiveness of the app serving model, and more.

Understanding the app size, deploying strategies to manage it, and knowing how to measure and diagnose its impact are crucial skills in Android app development as well as native Android development.

Importance of App Size Management

The size of your app can significantly affect the user's perception of your app. Bigger apps take more time to download, need more space on the device, and can cause friction with installations and updates. For users with limited data plans or slow network connections, this can be particularly problematic.

In the world of Android instant apps and competition to build optimized apps, your app's size is something you cannot ignore.

The Composition of App Size in Flutter

Before we jump into reducing the Flutter app size, it's crucial to understand what contributes to it. You need to know what you're dealing with to manage it effectively.

Debug vs Release Builds

While working on Flutter, developers usually deal with debug builds. They are typically larger due to additional debugging overhead that allows features like hot reload. Allocating more space for debugging symbols and other metadata significantly increases the size of the app bundle.

However, debug builds aren't representative of the final "user-facing" Flutter app size. The release builds, generated by running 'flutter build apk' or 'flutter build appbundle' for Android apps, are of significant importance as they represent the size of the app your user interacts with.

Android APKs and iOS IPAs: A Brief Introduction

In Android Studio, your Flutter app is compiled into an APK (Android Package Kit), while in Xcode, it is compiled into an IPA (iOS App Store Package). Both formats contain all the code and assets needed for the app.

In general, an IPA is larger than an APK primarily due to different structures and compression methods. This difference is also part of the reason why measuring app size is a bit tricky.

Tools to Measure App Size

Determining the size of the release version of a Flutter app isn't as straightforward as it might seem. Official app stores like the Google Play Store reprocess and split your upload package specifically for the downloader's hardware. That said, there are ways to get a close approximation.

Checking the Total Size

On completion of a build command, both for 'flutter build apk' and the 'flutter build appbundle', Flutter provides a summary of the app size. The two numbers represented are the .apk file size and the download size, which is an estimate of how much space is required to download your app from the Play Store. Note that they're not fully representative of your end-user's download and install size.

Estimating Download Size

Flutter provides instructions and tools to estimate the download size of your app. This can be notably different from comparing the size of the APK or IPA files due to the app-serving model used by the Google Play Store.

Android: Google Play Console

First, build an upload package for your app by running the 'flutter build appbundle' command. Afterward, log into your Google Play Console and upload the application binary (.aab file). The download and install size can be viewed in the "Android Vitals" -> "App size" tab.

iOS: Xcode App Size Report

For iOS, the process of estimating size involves a couple of stages. First, you'll have to run flutter build ipa --export-method development, and then open the archive in Xcode. The download size can be found in the App Thinning Size Report found in Xcode.

Breaking Down the App Size

Simply knowing the total size of your Flutter app isn't enough, especially when you're trying to minimize it. To reduce the compiled app size, you need to understand what contributes to it. For this purpose, Flutter provides a helpful size analysis tool.

Size Analysis in Flutter

Starting from Flutter version 1.22, developers can use the command 'flutter build apk --analyze-size' for the size analysis of their release build. This tool compiles Dart in a way that records the code size usage of Dart packages.

The result is a summary of the size breakdown in the terminal and a .json file for more detailed analysis in DevTools.

The size analysis tool is invoked by passing the --analyze-size flag when calling the build command.

Insights from Size Analysis Tools in Terminal

Familiarizing yourself with the size analysis tool can provide you with valuable insights about your Flutter app size, allowing you to make decisions based on these insights.

Size Usage per Category

When you run 'flutter build apk --analyze-size', the output in the terminal includes a high-level summary of your app size breakdown by category. This overview includes categories such as 'Dart AOT', 'lib arm64_v8a/', 'assets', and more, depending on your app.

You'll see which components are taking up the most space and have a baseline for where you might be able to make reductions.

High-Level Summary of Size Breakdown

The --analyze-size option also generates a detailed size summary in a '-code-size-analysis_.json' file. This file can be loaded into DevTools for deeper analysis, revealing where the space in your app is going at a package-, library-, class-, and even method level.

Deeper Analysis with DevTools

For a more granular understanding of your Flutter app size, nothing beats digging in with DevTools. This next-level tool allows you to analyze your app at the function level, leading to new insights about where you can make size reductions.

Understanding the Code-Size-Analysis Json File

The '-code-size-analysis_.json' file produced after running the 'flutter build apk --analyze-size' command contains a wealth of information. Loading this file into DevTools allows you to study the breakdown of your app's contents, even down to the function level.

Choose 'Open app size tool' and then upload the \-code-size-analysis_\.json file.

Using the DevTools App Size Tool

This powerful tool within DevTools provides a comprehensive analysis of the Dart AOT artifact. You can explore the tree map or adjust the view settings to match your requirements.

The Dart AOT snapshot (compiled to native arm code) takes up a significant portion of your app size. By understanding this space usage, you can refine your code, and shrink your app size.

Tips to Minimize Your Flutter App Size

Now that we've seen how to measure and analyze your Flutter app's size, it's time to tackle it head-on. Size optimization is a constant process that requires you to be proactive.

Implementing the --split-debug-info Tag

One of the most effective ways to reduce your Flutter app size is by using the --split-debug-info option. The main idea behind this tag is to dramatically reduce code size by splitting out the debug information. Let's see how we can use it:

Removing Unused Resources

Unused resources can add up over time, increasing your app size unnecessarily. Always remember to tidy up actively and remove unused images, fonts, and other assets. Tools like Android Studio itself can help to identify and delete these unused resources.

Minimizing Libraries Imports

The massive amount of readily available libraries in Flutter makes it easy to include functionality. However, ensure you're not needlessly adding in libraries for minor tasks and check to use only parts of libraries if possible.

Compressing PNG and JPEG Files

Your app's graphic assets can consume a lot of space. Consider compressing PNG and JPEG files using possible image compression options. Always explore SVG and WebP formats for smaller sizes.

Best Practices for Managing App Size in Flutter

In addition to the specific techniques mentioned earlier, there are some best practices when it comes to managing your Flutter app size. These practices will help you maintain a reasonable size throughout the life cycle of your app and save you much trouble in the end.

  1. Constant vigilance: Perform regular checks on your application size as you add features and make changes. This continuous monitoring will provide early alerts to any drastic size changes.
  2. Targeted asset delivery: Utilize Android's App Bundle to deliver only the necessary assets to each specific device configuration, reducing unnecessary usage.
  3. Diligent use of libraries: While libraries make app development significantly easier, they can also contribute to bloat. Use them judiciously and look for lighter alternatives when possible.
  4. Optimization from the start: Consider app size from the beginning of your project. Starting too late can lead to a lot of refactoring to bring down the size.

Wrapping Up!

App size is a critical aspect of app development that should never be overlooked. A leaner app makes for a smoother user experience, faster downloads, and better app performance. Managing your Flutter app's size isn't a one-size-fits-all task. However, with a bit of patience, diligence, and the use of the right tools, you can build apps that don't just function well but also stay within size boundaries that users appreciate.

And that's it! We hope you found this guide useful and gratifying. Keep building amazing apps, Flutter developers!

That concludes our blog on managing app size in Flutter. This has been a lot of information and I hope you found it helpful!

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