随着 Flutter 的逐渐发展与完善，与 Native 结合使用的场景越来越多；小菜今天尝试将一个历史的 Android Native 项目接入 Flutter Module；

AndroidX

      Flutter 的发展很迅速，大部分插件均适配 AndroidX，为了今后开发的便利性，小菜优先由如下版本升级适配 AndroidX；

minSdkVersion 17
targetSdkVersion 26

compileSdkVersion 28
buildToolsVersion "28.0.3"

      小菜以前尝试过 Flutter 升级适配 AndroidX，Android 的处理类似，小菜以实际项目尝试适配；

1. 添加 AndroidX 配置

      在 android/gradle.properties 文件中添加如下配置：

android.useAndroidX=true
android.enableJetifier=true

2. Migrate to AndroidX

      小菜通过 Android Studio 中的 Migrate to AndroidX 来配合升级(纯手动升级需要修改巨多的文件)，选择本工程 -> Refactor -> Migrate to Androidx；但小菜当前 Gradle 版本是 3.0.0，此时提示 Gradle 需 >= 3.2.0，故小菜需要先升级 Gradle；

3. Gradle 升级

      升级 android/build.gradle 文件中 Gradle 版本；此时 Sync 同步时会由如下两个提示；

classpath 'com.android.tools.build:gradle:3.2.0'

3.1 compile 已经不建议使用，小菜把各个 Module 中 compile 替换为 api / implementation；

Configuration 'compile' is obsolete and has been replaced with 'implementation' and 'api'.
It will be removed at the end of 2018. For more information see: http://d.android.com/r/tools/update-dependency-configurations.html

One of the plugins you are using supports Java 8 language features. To try the support built into the Android plugin, remove the following from your build.gradle:
    apply plugin: 'me.tatarka.retrolambda'
To learn more, go to https://d.android.com/r/tools/java-8-support-message.html

4. 重复第二步骤，Migrate to AndroidX

      注意要选择底部 Do Refactor，会帮我们节省巨大的工作量，只需要个别的文件引入或 xml 需要更改，否则需要我们手动修改大量的文件引入等；

5. Sync 同步打包检验

      若有个别 xml 文件需要调整，按照提示微调即可；debug / release 均需要打包检验；到此升级适配 AndroidX 工作基本完成；

Flutter Module

      小菜之前也尝试过 Android 原生集成 Flutter Module，小菜组内已有相关的 Flutter 工程，因此不再新建，集成方法很简单；

1. setting.gradle 中引入 Flutter Module 路径

setBinding(new Binding([gradle: this]))
evaluate(new File(
        '/Users/user/Documents/workspace/flutter_module02/.android/include_flutter.groovy'
))

2. app/build.project 中引入 Flutter 依赖

implementation project(':flutter')

3. Sync 同步后检验

      小菜以前整理过 Flutter 与 Android 原生交互，但为了验证方便小菜仅提供一个 FlutterActivity 供页面跳转即可；

public class FlutterMainActivity extends FlutterActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }
}

      小菜未使用 FlutterApplication，此时提示如下问题；

Caused by: java.lang.IllegalStateException: ensureInitializationComplete must be called after startInitialization
    at io.flutter.embedding.engine.loader.FlutterLoader.ensureInitializationComplete(FlutterLoader.java:153)
    at io.flutter.view.FlutterMain.ensureInitializationComplete(FlutterMain.java:80)
    at io.flutter.app.FlutterActivityDelegate.onCreate(FlutterActivityDelegate.java:144)
    at io.flutter.app.FlutterActivity.onCreate(FlutterActivity.java:89)
    at com.test.FlutterMainActivity.onCreate(FlutterMainActivity.java:13)
    at android.app.Activity.performCreate(Activity.java:6367)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2397)

      在 FlutterMainActivity 中提前初始化后，又提示新的问题；

protected void onCreate(@Nullable Bundle savedInstanceState) {
    FlutterMain.startInitialization(this);
    super.onCreate(savedInstanceState);
}

UncaughtException detected: java.lang.UnsatisfiedLinkError: dalvik.system.PathClassLoader[DexPathList[[zip file "/data/app/com.test-2/base.apk", zip file "/data/app/com.test-2/split_lib_dependencies_apk.apk", zip file "/data/app/com.test-2/split_lib_slice_0_apk.apk", zip file "/data/app/com.test-2/split_lib_slice_1_apk.apk"],nativeLibraryDirectories=[/data/app/com.test-2/lib/arm, /data/app/com.test-2/base.apk!/lib/armeabi, /data/app/com.test-2/split_lib_dependencies_apk.apk!/lib/armeabi, .../split_lib_slice_8_apk.apk!/lib/armeabi, /data/app/com.test-2/split_lib_slice_9_apk.apk!/lib/armeabi, /vendor/lib, /system/lib]]] couldn't find "libflutter.so"
    at java.lang.Runtime.loadLibrary(Runtime.java:379)
    at java.lang.System.loadLibrary(System.java:1086)
    at io.flutter.embedding.engine.loader.FlutterLoader.startInitialization(FlutterLoader.java:122)
    at io.flutter.embedding.engine.loader.FlutterLoader.startInitialization(FlutterLoader.java:93)
    at io.flutter.view.FlutterMain.startInitialization(FlutterMain.java:45)
    at com.test.FlutterMainActivity.onCreate(FlutterMainActivity.java:14)

      小菜查询后发现目前项目 NDK 只支持 armeabi 架构，而 Flutter 支持的时 armeabi-v7a，加入之后检验；若项目有特殊要求 NDK 必须是 armeabi 时，可考虑将 armeabi-v7a 的 flutter.so 拷贝到项目中；

ndk {
    abiFilters "armeabi", "armeabi-v7a", "x86"
}

小扩展

      小菜在适配 AndroidX 过程中还遇到如下问题，并非所有项目涉及，记录仅供参考；

Q1：All flavors must now belong to a named flavor dimension.

      小菜升级 Gradle 之后进行多渠道打包时会提示如下错误；

FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring project ':app'.
> All flavors must now belong to a named flavor dimension. Learn more at https://d.android.com/r/tools/flavorDimensions-missing-error-message.html
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
* Get more help at https://help.gradle.org
BUILD FAILED in 0s

A1：

      Gradle > 3.0 时多渠道打包需要指定一种 flavor dimensions；其中建议不要直接使用 main 的名称，否则容易出现新的重复键问题；com.android.build.gradle.internal.api.artifact.BuildableArtifactImpl

// 修改前
productFlavors {
  test1 {}
  test2 {}
  main {}
}
// 修改后
flavorDimensions "main"
productFlavors {
  test1 { dimension "main" }
  test2 { dimension "main" }
  main0 { dimension "main" }
}

Q2：com.android.builder.dexing.DexArchiveBuilderException

      小菜在运行过程中还提示 DexArchiveBuilderException 错误；

com.android.builder.dexing.DexArchiveBuilderException

A2：

      小菜查阅是未指定 Java8 的问题，添加指定 1.8 即可；

compileOptions {
    sourceCompatibility 1.8
    targetCompatibility 1.8
}

Q3：Unable to find method '...getOutputs()Ljava/util/List'

Error:Unable to find method 'com.android.build.gradle.api.BaseVariant.getOutputs()Ljava/util/List;'.
Possible causes for this unexpected error include:<ul><li>Gradle's dependency cache may be corrupt (this sometimes occurs after a network connection timeout.)
<a href="syncProject">Re-download dependencies and sync project (requires network)</a></li><li>The state of a Gradle build process (daemon) may be corrupt. Stopping all Gradle daemons may solve this problem.

A3：

      小菜几经查证后发现是 ButterKinfe 版本较低，因此升级至支持 AndroidX 的 10.2.1 的最新版本即可；注意，此时需要 Java8 环境；

dependencies {
  implementation 'com.jakewharton:butterknife:10.2.1'
  annotationProcessor 'com.jakewharton:butterknife-compiler:10.2.1'
}

      至此，小菜的历史项目升级适配 AndroidX 并接入 Flutter Module 基本完成，下一步是两者之间的交互；升级适配是一个艰难复杂的过程，可能会有很多意想不到的问题，希望可以沉下心来慢慢解决；如有问题请多多指导！

来源： 阿策小和尚