Flutter Android Build Process, Flavor Configuration, and SDK Bug Analysis

Flutter is a cross‑platform UI framework promoted by Google, but when building Android apps you still need native support such as Gradle flavor configuration and automatic generation of BuildConfig files.

The article demonstrates how to define three environments (development, test, production) in productFlavors { ... } and how to create separate entry files ( main_android_dev.dart, main_android_test.dart, main_android_online.dart) that initialize different AppConfig values before calling runApp().

Flavor‑specific APKs are built with the command:

flutter build apk --[debug|release] --flavor [flavor] -t lib/main_android_[flavor].dart

The Flutter build process starts from flutter_tools/bin/flutter_tools.dart, which invokes BuildCommand(). For Android, BuildApkCommand() eventually calls androidBuilder.buildApk(), which runs buildGradleApp() in flutter_tools/lib/src/android/gradle.dart. This method prepares the Gradle task, executes it, and checks the generated APK file.

The Gradle script reads local.properties to obtain the Flutter SDK path, version code, and version name, then applies flutter.gradle. The flutter.gradle file defines a FlutterTask that performs the actual compilation.

A bug in Flutter SDK 1.22.4 caused Gradle to look for an APK with a case‑sensitive name (e.g., app-flavorDev-debug.apk) while the generated file was lower‑cased ( app-flavordev-debug.apk). The SDK’s gradle.dart used apkFilesPaths.first without converting to lower case, leading to a “Gradle build failed to produce an .apk file” error on case‑sensitive file systems like Ubuntu.

Three work‑arounds are provided: (1) install the APK manually via adb install, (2) ensure all flavor names are lower‑case, or (3) modify the SDK source to use apkFilesPaths.first.toLowerCase() and clear the Flutter tool cache ( flutter/bin/cache/flutter_tools.*) to recompile the SDK.

The bug has been fixed in the master branch by using androidBuildInfo.buildInfo.lowerCasedFlavor when constructing the APK name.

In summary, the article walks through flavor configuration, multiple entry files, the full Flutter‑Android build pipeline, identifies a case‑sensitivity bug, and offers practical solutions without altering the SDK source.