Upgrading Flutter projects to Gradle 4.1 and Android Studio Gradle plugin 3.0.1

(This wiki page applies to people migrating code written before December 2017. It is unlikely to still be relevant.)

Introduction

Prior to #13492 (merged on 2017-12-13), Flutter tooling created projects whose Android part used Gradle 3.3 and the Android Studio Gradle plugin version 2.3.3.

After #13492, Flutter tooling creates projects based on Gradle 4.1 and the Android Studio Gradle plugin version 3.0.1.

This page describes how you can manually upgrade your Flutter projects from the old mode to the new one. This may be needed to consume new-mode Flutter plugins.

Where in doubt, please consult https://developer.android.com/studio/build/gradle-plugin-3-0-0-migration.html.

Upgrading a Flutter app project

1. In android/gradle/wrapper/gradle-wrapper.properties, replace 3.3 with 4.1 in the last line.

2. In android/build.gradle, replace

   repositories {
       jcenter()
       maven {
           url "https://maven.google.com"
       }
   }

   by

   repositories {
       google()
       jcenter()
   }

   twice.

   Also replace

   dependencies {
       classpath 'com.android.tools.build:gradle:2.3.3'
   }

   by

   dependencies {
       classpath 'com.android.tools.build:gradle:3.0.1'
   }

   Finally, replace

   subprojects {
       project.buildDir = "${rootProject.buildDir}/${project.name}"
       project.evaluationDependsOn(':app')
   }

   by

   subprojects {
       project.buildDir = "${rootProject.buildDir}/${project.name}"
   }
   subprojects {
       project.evaluationDependsOn(':app')
   }

   This change prevents a "Gradle build failed to produce an Android package" error message when your app depends on plugins whose name comes before "app" in lexicographic order.

3. In android/app/build.gradle, replace version 25 by 27 and 25.0.3 by 27.0.3 (three places total).

   If you are using a version of Flutter from before #13558, add the following to the android,buildTypes section:

   profile {
       matchingFallbacks = ['debug', 'release']
   }

   Replace configurations named compile by api (or implementation) and provided by compileOnly in the dependencies section. You may also want to update dependencies with newer versions as applicable. In the default project templates generated by Flutter tooling we have replaced

   dependencies {
       androidTestCompile 'com.android.support:support-annotations:25.4.0'
       androidTestCompile 'com.android.support.test:runner:0.5'
       androidTestCompile 'com.android.support.test:rules:0.5'
   }

   by

   dependencies {
       testImplementation 'junit:junit:4.12'
       androidTestImplementation 'com.android.support.test:runner:1.0.1'
       androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
   }

   loosely following the lead of Android Studio.

Upgrading a Flutter plugin project

1. Upgrade the example/ Flutter app project as indicated above.

2. Remove the Gradle wrapper files and folder (gradlew, gradlew.bat, gradle/) from the top-level android folder, if present. The Gradle wrapper is used by the example app only, and it should already contain these files.

3. In android/build.gradle, replace

   repositories {
       jcenter()
       maven {
           url "https://maven.google.com"
       }
   }

   by

   repositories {
       google()
       jcenter()
   }

   twice.

   Also replace

   dependencies {
       classpath 'com.android.tools.build:gradle:2.3.3'
   }

   by

   dependencies {
       classpath 'com.android.tools.build:gradle:3.0.1'
   }

   Replace version 25 by 27 and 25.0.3 by 27.0.3.

   Lastly, replace configurations named compile by api (or implementation) and provided by compileOnly in any custom dependencies section.