How to migrate old Flutter project to the latest Flutter version

Migrating an old Flutter project (using older Android Gradle and build.gradle Groovy files) to the latest Flutter version (3.22) which now defaults to Kotlin DSL (build.gradle.kts), involves several steps.

Objective:

Migrate your existing android/build.gradle, android/app/build.gradle, and related files from Groovy (.gradle) to Kotlin DSL (.gradle.kts) format while ensuring compatibility with Flutter 3.22 and AGP (Android Gradle Plugin) 8+.

Step-by-step Migration Guide:

1. Upgrade Flutter SDK to 3.22

Make sure you’re on Flutter 3.22:

flutter upgrade
flutter --version

2. Backup Your Project

Before any change, back up your current project (e.g. via Git or zip).

3. Update Gradle Wrapper

Edit android/gradle/wrapper/gradle-wrapper.properties:

distributionUrl=https\://services.gradle.org/distributions/gradle-8.4-all.zip

Gradle 8.4 is compatible with AGP 8.4+ and Kotlin DSL.

4. Convert Groovy .gradle to Kotlin DSL .gradle.kts

Rename:

• android/build.gradle → android/build.gradle.kts
• android/app/build.gradle → android/app/build.gradle.kts
• Update settings.gradle → settings.gradle.kts

5. Edit build.gradle.kts (Project-level)

Example android/build.gradle.kts:

// File: android/build.gradle.kts
buildscript {
    dependencies {
        classpath("com.android.tools.build:gradle:8.4.0")
        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.24")
    }
}

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

6. Edit app/build.gradle.kts (App-level)

Here’s a minimal example for android/app/build.gradle.kts:

// File: android/app/build.gradle.kts
plugins {
    id("com.android.application")
    kotlin("android")
}

android {
    namespace = "com.example.yourapp"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.example.yourapp"
        minSdk = 21
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"
    }

    buildTypes {
        release {
            isMinifyEnabled = false
            proguardFiles(
                getDefaultProguardFile("proguard-android-optimize.txt"),
                "proguard-rules.pro"
            )
        }
    }
}

dependencies {
    implementation("androidx.core:core-ktx:1.13.1")
    implementation("androidx.appcompat:appcompat:1.6.1")
}

7. Update settings.gradle.kts

Replace settings.gradle with settings.gradle.kts:

// File: android/settings.gradle.kts
include(":app")

8. Update Flutter Build Configuration

Make sure flutter.gradle is still referenced. You might need to update:

// android/build.gradle.kts (under buildscript)
classpath("com.google.gms:google-services:4.4.0")
classpath("com.android.tools.build:gradle:8.4.0")
classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.24")

In app/build.gradle.kts, apply:

apply(from = "../flutter.gradle.kts")

9. Update Gradle Properties

Edit android/gradle.properties:

propertiesCopyEditorg.gradle.jvmargs=-Xmx2048m
android.useAndroidX=true
kotlin.code.style=official

10. Clean and Build

flutter clean
flutter pub get
flutter build apk

Common Issues:

Final Tip

If you want a fully working sample with Kotlin DSL, create a new Flutter project with:

flutter create --platforms android -a kotlin my_new_app

Then compare the android/ folder structure and Kotlin DSL syntax with your project.

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