Deprecated imperative apply of Flutter's Gradle plugins

To build a Flutter app for Android, Flutter's Gradle plugins must be applied. Historically, this was done imperatively with Gradle's legacy, imperative apply script method.

In Flutter 3.16, support was added for applying these plugins with Gradle's declarative plugins {} block (also called the Plugin DSL) and it is now the recommended approach. Since Flutter 3.16, projects generated with flutter create use the Plugin DSL to apply Gradle plugins. Projects created with versions of Flutter prior to 3.16 need to be migrated manually.

Applying Gradle plugins using the plugins {} block executes the same code as before and should produce equivalent app binaries.

To learn about advantages the new Plugin DSL syntax has over the legacy apply script syntax, see Gradle docs.

Migrating the app ecosystem to use the new approach will also make it easier for Flutter team to develop Flutter's Gradle plugins, and to enable exciting new features in the future, such as using Kotlin instead of Groovy in Gradle buildscripts.

First, find the values of the Android Gradle Plugin (AGP) and Kotlin that the project currently uses. Unless they have been moved, they are likely defined in the buildscript block of the <app-src>/android/build.gradle file. As an example, consider the build.gradle file from a new Flutter app created before this change:

buildscript {
    ext.kotlin_version = '1.7.10'
    repositories {
        google()
        mavenCentral()
    }

    dependencies {
        classpath 'com.android.tools.build:gradle:7.3.0'
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
    }
}

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

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

tasks.register("clean", Delete) {
    delete rootProject.buildDir
}

The AGP version is the number that comes at the end of the line classpath 'com.android.tools.build:gradle:7.3.0', so 7.3.0 in this case. Similarly, the Kotlin version comes at the end of the line ext.kotlin_version = '1.7.10', in this case 1.7.10.

Next, replace the contents of <app-src>/android/settings.gradle with the below, remembering to replace {agpVersion} and {kotlinVersion} with previously identified values:

pluginManagement {
    def flutterSdkPath = {
        def properties = new Properties()
        file("local.properties").withInputStream { properties.load(it) }
        def flutterSdkPath = properties.getProperty("flutter.sdk")
        assert flutterSdkPath != null, "flutter.sdk not set in local.properties"
        return flutterSdkPath
    }()

    includeBuild("$flutterSdkPath/packages/flutter_tools/gradle")

    repositories {
        google()
        mavenCentral()
        gradlePluginPortal()
    }
}

plugins {
    id "dev.flutter.flutter-plugin-loader" version "1.0.0"
    id "com.android.application" version "{agpVersion}" apply false
    id "org.jetbrains.kotlin.android" version "{kotlinVersion}" apply false
}

include ":app"

If you made some changes to this file, make sure they're placed after pluginManagement {} and plugins {} blocks, since Gradle enforces that no other code may be placed before these blocks.

Remove the whole buildscript block from <app-src/android/build.gradle:

-buildscript {
-    ext.kotlin_version = '{kotlinVersion}'
-    repositories {
-        google()
-        mavenCentral()
-    }
-
-    dependencies {
-        classpath "org.jetbrains.kotlin:gradle-plugin:$kotlin_version"
-    }
-}

Here's how that file will likely end up:

allprojects {
    repositories {
        google()
        mavenCentral()
    }
}

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

tasks.register("clean", Delete) {
    delete rootProject.buildDir
}

Most changes have to be made in the <app-src>/android/app/build.gradle. First, remove these 2 chunks of code that use the legacy imperative apply method:

-def flutterRoot = localProperties.getProperty('flutter.sdk')
-if (flutterRoot == null) {
-    throw new GradleException("Flutter SDK not found. Define location with flutter.sdk in the local.properties file.")
-}

-apply plugin: 'com.android.application'
-apply plugin: 'com.jetbrains.kotlin.android'
-apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"

Now apply the plugins again, but this time using the Plugin DSL syntax. At the very top of your file, add:

+plugins {
+    id "com.android.application"
+    id "kotlin-android"
+    id "dev.flutter.flutter-gradle-plugin"
+}

Finally, if your dependencies block contains a dependency on "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version", then remove that dependency.

dependencies {
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
}

If it was the only dependency in the dependencies block, then alternatively you may remove the block entirely.

Execute flutter run to confirm your app builds and launches on a connected Android device or emulator.

If your app was using Google Mobile Services and Crashlytics, remove the following lines from <app-src>/android/build.gradle:

 buildscript {
     // ...

     dependencies {
         // ...
-        classpath "com.google.gms:google-services:4.4.0"
-        classpath "com.google.firebase:firebase-crashlytics-gradle:2.9.9"
     }
 }

and remove these 2 lines from <app-src>/android/app/build.gradle:

-apply plugin: 'com.google.gms.google-services'
-apply plugin: 'com.google.firebase.crashlytics'

To migrate to the new, declarative apply of the GMS and Crashlytics plugins, add the following lines to <app-src>/android/settings.gradle:

 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "{agpVersion}" apply false
     id "org.jetbrains.kotlin.android" version "{kotlinVersion}" apply false
+    id "com.google.gms.google-services" version "4.4.0" apply false
+    id "com.google.firebase.crashlytics" version "2.9.9" apply false
 }

and the following lines to <app-src>/android/app/build.gradle:

 plugins {
     id "com.android.application"
     id "dev.flutter.flutter-gradle-plugin"
     id "org.jetbrains.kotlin.android"
+    id "com.google.gms.google-services"
+    id "com.google.firebase.crashlytics"
 }

Support in stable release: 3.16.0 Recommended in stable release: 3.19.0

Gradle build files generated by flutter create differ across Flutter versions. For a detailed overview, see issue #135392. You should consider using the latest versions of build files.