Why does my build fail? ​

Flutter utilizes native build systems on Android and iOS. As these systems evolve and introduce additional features on their own pace, developers sometimes need to re-adjust the configuration to prevent build failures.

This page collects such errors and the standard procedure to work around them.

Android ​

Android builds are handled by the Gradle tool, which is configured using .gradle files. Android Apps themselves are packaged, compiled & optimized by a variety of tools - all being orchestrated by the Android Gradle Plugin (AGP).

Usually, Android Studio and AGP are aligned in their versions. Android Studio also contains a few assistants to smoothen the upgrade process for existing projects.

Quick Fix (suitable for most build errors) ​

• Open Android Studio
• Use the File Menu, then "Check for Updates" & retrieve the latest version if necessary
• After the upgrade, use the File Menu and open the "android/build.gradle" or "example/android/build.gradle" file directly. Android Studio will then import the Android portion of the project and will offer you to upgrade the Gradle plugin and the Gradle wrapper
• If you develop a plugin, you need to manually check android/build.gradle and example/android/build.gradle afterwards and ensure they are referring to the same AGP version

Minimum supported Gradle version is 5.4.1. Current version is 4.10.2. ​

In this example, the Gradle plugin upgrade was stopped mid-way and the build can not continue.

To fix it, open android/gradle/wrapper/gradle-wrapper.properties (example/android/gradle/wrapper/gradle-wrapper.properties if you develop a plugin) and replace the version in there with the required version.

The Android Gradle plugin only supports Kotlin Gradle Plugin 1.3.10 or higher ​

With the steps above, only AGP and the wrapper got upgraded. The Kotlin compiler infrastructure is a secondary dependency which is also dependent on certain AGP/Gradle versions. To resolve it:

• Scan your build.gradle files for a placeholder like ext.kotlin_version = '1.2.71' and replace it with the latest Kotlin version (or the version named in the error message).
• Android Studio can recommend the latest version, if you open the build.gradle file in it
• New Kotlin versions introduce language & syntax optimizations; it is therefore recommended to use Android Studio again and open the native part of the App (see above) and let it run a full compilation, including a clean operation. Android Studio will report build failures and suggestions to optimize your code.

Gradle task assembleDebug failed with exit code 1 ​

If assembleDebug or assembleRelease failed but no error message can be seen, you are likely on a older Flutter version (<= 1.9.1.hotfix4) which may suppress the root cause of the error.

This problem can be solved in two ways:

• Please try a more recent channel, like beta or dev and restart the compilation. It may still fail, but the error will now be printed
• Open the $FLUTTER_ROOT/packages/flutter_tools/gradle/flutter.gradle file in your local installation and comment the line which reads gradle.useLogger(new FlutterEventLogger()), then retry your build