Introduction

Spent a day upgrading the architecture of Youmengji from Flutter 2 to Flutter 3. Here’s a summary of the pitfalls encountered.

Upgrading Flutter Version

• Check current version:

  • flutter --version

• Upgrade Flutter (requires VPN access):

  • flutter upgrade

• Verify version (should start with 3.x):

  • flutter --version

• If you’re lucky enough to run the app directly after this, you can stop reading here.

compileSdkVersion Error

• Modify compileSdkVersion to 33 in android/app/build.gradle
• Update distributionUrl in android/gradle/wrapper/gradle-wrapper.properties:

  distributionUrl=https\://services.gradle.org/distributions/gradle-7.4-all.zip
  

• Update Gradle plugin in android/build.gradle:

  classpath 'com.android.tools.build:gradle:7.1.2'
  

• Update SDK via Android Studio’s SDK Manager:

  

  

Warning: Mapping new ns xxx to old ns xxx

• Modify repository URLs in android/build.gradle:

  // From:
  maven { url 'http://maven.aliyun.com/nexus/content/groups/public' }
  // To:
  maven { url 'https://maven.aliyun.com/repository/public' }
  

Error: No named parameter with the name ‘maxLengthEnforced’

• Common issue with deprecated parameters after Flutter upgrades.
• Solution:
  1. Update all dependencies to their latest versions
  2. Follow migration guides for breaking changes in SDKs

No signature of method: .android() in build.gradle (app)

• Remove useProguard configuration in android/app/build.gradle:

  buildTypes {
      release {
          minifyEnabled true
          // Delete this line
          proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
  }
  

JAR Version Conflict Warning

• Ensure Kotlin version consistency:

  ext.kotlin_version = '1.7.10'
  dependencies {
      classpath 'com.android.tools.build:gradle:7.2.0'
      classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
  }
  

• Pro tip: Create a new Flutter project (flutter new app) to compare with fresh configuration files.