What is the android/ Folder?

When you create a new Flutter project, you get several folders like lib/, ios/, test/, and android/. Among these, the android folder plays a very special role. It is the bridge between your Flutter project and the native Android ecosystem.

Even though Flutter allows you to write most of your application logic in Dart (inside the lib/ folder), you still need Android-specific configurations and files to ensure your app can run properly on Android devices.

This article will give you a deep dive into the android/ folder in a Flutter project, covering:

Why the android folder exists
The structure of the folder
Important files like build.gradle and AndroidManifest.xml
How Firebase setup works inside it
Using native libraries and custom Android code
Best practices for working with the android folder

By the end of this guide, you will clearly understand what the android folder does, when you need to use it, and how to avoid common mistakes.

Why Does the android/ Folder Exist in a Flutter Project?

Flutter is a cross-platform framework, meaning it allows you to write one codebase that works on multiple platforms such as Android, iOS, web, and desktop. However, each platform still has its own requirements.

For Android, Flutter relies on the native Android project structure in order to:

Configure and build the app with Gradle (the Android build system).
Manage app-level settings such as permissions, themes, and app icons.
Integrate native Android features when Flutter itself does not provide direct access.
Handle dependencies like Firebase that require Android-specific configuration.

In short, without the android folder, your Flutter project would not be able to run on Android devices.

Structure of the android/ Folder

When you open the android folder inside your Flutter project, you’ll notice that it looks like a traditional Android project. In fact, it is a full-fledged Android project created automatically by Flutter.

A typical structure looks like this:

android/
 ├── app/
 │    ├── src/
 │    │    ├── main/
 │    │    │   ├── AndroidManifest.xml
 │    │    │   ├── java/
 │    │    │   └── res/
 │    └── build.gradle
 ├── gradle/
 ├── gradle.properties
 ├── build.gradle
 ├── settings.gradle
 └── local.properties

Let us go through each important part one by one.

The Gradle Build System

Android apps are built using Gradle, which is a powerful build automation tool. Flutter uses Gradle under the hood to compile your Dart code into native Android binaries (APK or AAB).

There are two important build.gradle files inside the android folder:

Project-level build.gradle (inside android/build.gradle)
App-level build.gradle (inside android/app/build.gradle)

Project-Level build.gradle

This file manages overall project configuration. It defines repositories where Gradle will look for dependencies and includes global plugins.

For example, you will see references to Maven Central, Google’s Maven repository, and Gradle plugins here.

App-Level build.gradle

This is the most important build file for Flutter developers. It defines how your actual Android app is built. Some of the key things managed here include:

Application ID (unique identifier for your app on the Play Store).
Minimum SDK version and target SDK version.
Version code and version name (important for app updates).
Linking third-party libraries.
Configuration for release builds (signing and optimization).

In most real-world Flutter projects, you will make changes in the app-level build.gradle file when setting up Firebase, enabling multidex, or updating SDK versions.

AndroidManifest.xml – The Identity of Your App

Another critical file inside the android folder is AndroidManifest.xml. This file acts as the blueprint of your Android application. It tells the Android operating system about your app’s essential information, such as:

The app’s package name.
Permissions the app needs (e.g., internet, camera, location).
The main activity that should launch first.
App icons and themes.

For example, if you want to use the internet in your app, you must declare it in the manifest like this:

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

If you forget to declare a permission in this file, your app will not be able to access that feature, even if you write the Dart code correctly.

The manifest file is also where you integrate features such as push notifications, background services, and intent filters.

Firebase Setup in the android/ Folder

Firebase is one of the most popular backend services for Flutter apps. It provides authentication, databases, cloud storage, push notifications, analytics, and more.

When you integrate Firebase into your Flutter project, the android folder is where you perform the setup for the Android side.

The steps typically involve:

Adding google-services.json
- This file is downloaded from the Firebase console and placed inside android/app/.
- It contains credentials that link your app with your Firebase project.
Updating build.gradle files
- At the project-level, you add the Google services classpath.
- At the app-level, you apply the Google services plugin and add Firebase dependencies.
Configuring AndroidManifest.xml
- You may need to add Firebase-related metadata or services here, such as enabling Firebase messaging for push notifications.

Without proper setup inside the android folder, Firebase features will not work on the Android side of your Flutter app.

Native Libraries and Custom Code

Sometimes, Flutter’s plugins are not enough for your project. You may want to use a specific Android library written in Java or Kotlin, or you may need to access low-level APIs that Flutter does not expose.

The android folder gives you the flexibility to:

Write custom native code in Java or Kotlin.
Expose that code to Flutter using platform channels.
Add third-party Android libraries directly in the app-level build.gradle file.

For example, if you want to integrate an advanced video player library available only in Android, you can do it through the android folder.

This ability to drop down into native code when required is one of the strengths of Flutter. It ensures that you are never limited by what Flutter provides out of the box.

Other Important Files in the android/ Folder

Apart from build.gradle and AndroidManifest.xml, there are several other files worth mentioning:

gradle.properties: Stores Gradle settings, like JVM arguments and optimization flags.
settings.gradle: Configures project modules for Gradle.
local.properties: Stores local environment settings, such as the path to the Android SDK. This file should not be committed to version control.
res folder: Contains resources such as images, colors, themes, and XML layouts. Even though most UI comes from Flutter, some Android-specific resources may still live here (like notification icons or splash screen assets).

When Do You Need to Touch the android/ Folder?

As a Flutter developer, most of your work happens in the lib/ folder. However, there are specific situations where you must modify files inside the android folder. These include:

Setting the minimum SDK version for your app.
Adding new permissions such as internet, camera, or location.
Configuring Firebase or other third-party SDKs.
Customizing splash screens and app icons.
Writing custom native code in Java or Kotlin.
Updating signing configurations for releasing the app on the Play Store.

If you are building simple apps, you might not touch this folder at all. But for production-level apps, it is almost always necessary to make changes here.

Best Practices for Working with the android/ Folder

Don’t edit blindly. Many beginners break their projects by making incorrect changes in build.gradle or the manifest. Always understand what you are changing.
Use version control. Keep backups of working configurations. Git will save you if you make mistakes.
Match SDK versions carefully. Using outdated or mismatched SDK versions can cause build failures.
Follow documentation. When integrating libraries like Firebase, always follow the official FlutterFire documentation.
Keep custom code separate. If you write native code, try to keep it well-documented so that other team members understand what it does.