在现有项目上集成Flutter
1.在andorid工程目录上级目录下执行命令:
flutter create -t module xxxx(想要创建的flutter项目名)
执行完后，一个和Android项目平级的flutter项目就已经创建好了。
2.添加flutter到当前Android项目：
在Android项目根目录下的settings.gradle文件中，添加如下代码：
setBinding(new Binding([gradle: this]))
evaluate(new File(
settingsDir.parentFile,
"flutter_hybrid/.android/include_flutter.groovy"
))
然后，在项目的app目录下，build.gradle文件中，添加如下dependency:
implementation project(':flutter')
如上，添加完之后，准备工作就完成了。
集成Flutter页面跳转
通过继承FlutterActivity跳到默认页面
1.Application：初始化Flutter
public class App extends Application {
@Override
public void onCreate() {
super.onCreate();
FlutterMain.startInitialization(this);
}
}
2.Activity：继承FlutterActivity
/**
* debug模式原生跳转到flutter界面会出现白屏，release包就不会出现白屏了
*/
public class MainFlutterActivity extends FlutterActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
GeneratedPluginRegistrant.registerWith(this);
}
这样以后，我们就可以跳转这个MainFlutterActivity，实现在Android工程里面进入Flutter工程的默认页面了。
通过FlutterView跳到指定页面
首先通过Flutter.createFlutterView方法来创建一个FlutterView类型的View。它有三个构造参数：
public static FlutterView createView(Activity activity, Lifecycle lifecycle, String initialRoute)
三个参数分别是：
1.Activity，即当前附着的Activity
2.LifeCycle，且是不能为空(NonNull)的，这也就要求我们必须用AppCompatActivity来承载FlutterView了，如果我们的Activity继承自android.app.Activity是没有getLifeCycle()这个方法的。
public class FlutterViewActivity extends AppCompatActivity 复制代码
3.initialRoute这是一个String类型的变量，根据不同的标识跳转不同的Flutter页面：
Widget _widgetForRoute(String route) {
switch (route) {
case 'route1':
return MyHomePage(title: 'Flutter Demo Home Page1');
case 'route2':
return MyHomePage(title: 'Flutter Demo Home Page2');
default:
return MyHomePage(title: 'Flutter Demo Home Page2');
}
}
然后在当前Activity的OnCreate方法中，执行：
FlutterView flutterView = Flutter.createView(this, getLifecycle(), "route1");
setContentView(flutterView);
//或者：
setContentView(R.layout.activity_flutter);
rlContainer = findViewById(R.id.rl_container);
rlContainer.addView(flutterView)
集成到现有项目遇到的坑
Check failed: vm. Must be able to initialize the VM：
E/flutter: [ERROR:flutter/runtime/dart_vm_data.cc(19)] VM snapshot invalid and could not be inferred from settings.
[ERROR:flutter/runtime/dart_vm.cc(241)] Could not setup VM data to bootstrap the VM from.
[ERROR:flutter/runtime/dart_vm_lifecycle.cc(89)] Could not create Dart VM instance.
A/flutter: [FATAL:flutter/shell/common/shell.cc(218)] Check failed: vm. Must be able to initialize the VM.
SIGABRT
0x146b
#00 pc 0002210c /system/lib/libc.so (tgkill+12) [armeabi-v7a::ac712d92afdda143205c7d7c8befc336]
#01 pc 00013165 /system/lib/libc.so (pthread_kill+48) [armeabi-v7a::ac712d92afdda143205c7d7c8befc336]
#02 pc 00013379 /system/lib/libc.so (raise+10) [armeabi-v7a::ac712d92afdda143205c7d7c8befc336]
#03 pc 000120a3 /system/lib/libc.so [armeabi-v7a::ac712d92afdda143205c7d7c8befc336]
#04 pc 000219c0 /system/lib/libc.so (abort+4) [armeabi-v7a::ac712d92afdda143205c7d7c8befc336]
#05 pc 00af85ab /data/app-lib/xxx.debug-1/libflutter.so [armeabi-v7a::a12434e0b53806a35730000001000000]
经github上#24679及其他issue参考，得出以下解决方案：
Import flutter module to your HOST app(set binding, implementation, and instantiate view/fragment)
When you clean/rebuild from HOST app, flutter module does not generate properly
You need to open your flutter module in a separate AS
flutter clean
cd .android
./gradlew clean
./gradlew assembleDebug
Return to host app and run app(do not sync or rebuild) :)
翻译过来就是：
本项目执行清理命令。./gradlew clean
进入 flutter module 项目执行清理命令。flutter packages get;flutter clean
进入 flutter module 的 .android 项目执行清理命令和打包操作。./gradlew clean;./gradlew assemble
回到本项目执行打包命令。./gradlew assemble
直接执行下面命令即可：
$ ./gradlew clean;cd ../flutter_module;flutter packages get;flutter clean;cd .android/;./gradlew clean;./gradlew assemble;cd /d/workspace/app_proj/;./gradlew installDebug
后续假设你 flutter module 没有更新过，那么以后修改本地项目之后，就直接执行./gradlew installDebug。 注意不要用studio工具运行、rebuild或clean。
flutter_assets
assets下缺少flutter_assets也有可能造成此问题。具体可以参考：https://www.jianshu.com/p/2d0bba84e57e
混淆
按照上述方式，debug版本没问题，release却报错。需加以下混淆：
-keep class io.flutter.app.** { *; }
-keep class io.flutter.plugin.* { *; }
-keep class io.flutter.util.* { *; }
-keep class io.flutter.view.* { *; }
-keep class io.flutter.* { *; }
-keep class io.flutter.plugins.* { *; }
-keep class myapp.flutter.*
参考资料
https://github.com/chinaltz/FlutterDemo
https://juejin.im/post/5c74dbeee51d45708f2a20c6
https://github.com/flutter/flutter/issues/24679
https://github.com/flutter/flutter/issues/25147
https://mp.weixin.qq.com/s/OGbH3G3wHVTUt-0EJit8RA
