随着 Flutter 的逐渐发展与完善，与 Native 结合使用的场景越来越多；和尚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，和尚优先由如下版本升级适配 AndroidX；
代码语言：javascript复制minSdkVersion 17
targetSdkVersion 26
compileSdkVersion 28
buildToolsVersion "28.0.3"和尚以前尝试过 Flutter 升级适配 AndroidX[1]，Android 的处理类似，和尚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：
代码语言：javascript复制android.useAndroidX=true
android.enableJetifier=true2. Migrate to AndroidX
和尚通过 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；但和尚当前 Gradle 版本是 3.0.0，此时提示 Gradle 需 >= 3.2.0，故和尚需要先升级 Gradle；
3. Gradle 升级
升级 android/build.gradle 文件中 Gradle 版本；此时 Sync 同步时会有如下两个提示；
代码语言：javascript复制classpath 'com.android.tools.build:gradle:3.2.0'3.1 compile 已经不建议使用，和尚把各个 Module 中 compile 替换为 api / implementation；
代码语言：javascript复制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
3.2 和尚的项目中在之前通过 retrolambda 支持 Java8，在 Gradle > 3.0.0 之后默认支持 Java8，和尚将引入去掉即可；
代码语言：javascript复制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；
android.support | androidx |
|---|---|
android.support.annotation.NonNull; | androidx.annotation.NonNull; |
android.support.annotation.Nullable; | androidx.annotation.Nullable; |
android.support.annotation.IntRange; | androidx.annotation.IntRange; |
android.support.design.widget.CoordinatorLayout; | androidx.coordinatorlayout.widget.CoordinatorLayout; |
android.support.v4.content.ContextCompat; | androidx.core.content.ContextCompat; |
android.support.v4.widget.DrawerLayout; | androidx.drawerlayout.widget.DrawerLayout; |
android.support.v4.app.Fragment; | androidx.fragment.app.Fragment; |
android.support.v4.graphics.drawable.RoundedBitmapDrawable; | androidx.core.graphics.drawable.RoundedBitmapDrawable; |
android.support.v4.graphics.drawable.RoundedBitmapDrawableFactory; | androidx.core.graphics.drawable.RoundedBitmapDrawableFactory; |
android.support.v7.widget.RecyclerView; | androidx.recyclerview.widget.RecyclerView; |
android.support.v7.app.AlertDialog; | androidx.appcompat.app.AlertDialog; |
... | ... |
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
和尚之前也尝试过 Android 原生集成 Flutter Module[2]，和尚组内有相关的 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
代码语言：javascript复制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
代码语言：javascript复制implementation project(':flutter')3. Sync 同步后检验
和尚以前整理过 Flutter 与 Android 原生交互[3]，但为了验证方便和尚仅提供一个 FlutterActivity 供页面跳转即可；
代码语言：javascript复制public class FlutterMainActivity extends FlutterActivity {
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
}和尚未使用 FlutterApplication，此时提示如下问题；
代码语言：javascript复制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；
代码语言：javascript复制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)和尚查询后发现目前项目 NDK 只支持 armeabi 架构，而 Flutter 支持的是 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；
代码语言：javascript复制ndk {
abiFilters "armeabi", "armeabi-v7a", "x86"
}
小扩展
和尚在适配 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.
和尚升级 Gradle 之后进行多渠道打包时会提示如下错误；
代码语言：javascript复制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 0sA1：
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
代码语言：javascript复制// 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
和尚在运行过程中还提示 DexArchiveBuilderException 错误；
代码语言：javascript复制com.android.builder.dexing.DexArchiveBuilderExceptionA2：
和尚查阅是未指定 Java8 的问题，添加指定 1.8 即可；
代码语言：javascript复制compileOptions {
sourceCompatibility 1.8
targetCompatibility 1.8
}Q3：Unable to find method '...getOutputs()Ljava/util/List'
代码语言：javascript复制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：
和尚几经查证后发现是 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；
代码语言：javascript复制dependencies {
implementation 'com.jakewharton:butterknife:10.2.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:10.2.1'
}至此，和尚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
References
[1] Flutter 升级适配 AndroidX: https://www.jianshu.com/p/601eb858d507
[2] Android 原生集成 Flutter Module: https://www.jianshu.com/p/aab477e49ce4
[3] Flutter 与 Android 原生交互: https://www.jianshu.com/p/22939eaa47b1
