体验后，发现官方的flutter混合编程不支持androidx，下文为安卓工程支持androidx为例的。
flutter技术不断更新，以flutter官方更新为准

本文笔记代码 github

体验Flutter混合开发

下面以Android项目为例，体验Flutter混合开发，Android Flutter混合开发，指的是在普通的安卓工程里，把Flutter以普通第三方类库的形式集成进来，官方有两种集成方式，一种是Flutter以aar形式集成到安卓工程，一种是以源码的形式依赖进安卓工程，源码的形式开发时比较方便，下面以flutter工程以安卓源码模块的方法集成进安卓工程为例

官方原文可以查看这里

IOS混合开发，请点击这里

1.创建Android工程

Android Studio -> New Project -> Empty Activity

创建工程后，gradle 需要添加一些配置

因为
Flutter currently only supports building ahead-of-time (AOT) compiled libraries for armeabi-v7a and arm64-v8a.

所以

要在 app目录下的build.gradle下添加

ndk {
      // Filter for architectures supported by Flutter.
      abiFilters 'armeabi-v7a', 'arm64-v8a'
    }

因为The Flutter Android engine uses Java 8 features.

所以还要添加

 compileOptions {
    sourceCompatibility 1.8
    targetCompatibility 1.8
  }

添加后如下所示

android {
    compileSdkVersion 29
    buildToolsVersion "29.0.2"
    defaultConfig {
        applicationId "com.example.androidapplication"
        minSdkVersion 16
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        ndk {
            // Filter for architectures supported by Flutter.
            abiFilters 'armeabi-v7a', 'arm64-v8a'
        }
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }

    compileOptions {
        sourceCompatibility 1.8
        targetCompatibility 1.8
    }
}

创建Flutter Module

File -> New Flutter Project -> Flutter Module

创建后，工程如下

AndroidFlutter混合开发.png

创建后的flutter_module可以用AndroidStudio用一个新窗口重新打开，并且打开后flutter_module 其实是可以独立编译安装成一个app的。

配置依赖Flutter Module

创建完Flutter Module后，在安卓工程项目的settings.gradle里添加

setBinding(new Binding([gradle: this]))  
evaluate(new File(                                                   
    settingsDir.parentFile,                                            
    '你的安卓项目名称/flutter_module/.android/include_flutter.groovy'       
))

app/build.gradle里添加如下依赖

implementation project(':flutter')

向 Android 应用中添加 Flutter 页面

1.在安卓工程的app/src/main/AndroidManifest.xml里添加

    <activity
        android:name="io.flutter.embedding.android.FlutterActivity"
        android:theme="@style/AppTheme"
        android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
        android:hardwareAccelerated="true"
        android:windowSoftInputMode="adjustResize"
        />

2.在安卓代码里调起FlutterActivity

启动主页

   //kotlin代码
   startFlutterActivity.setOnClickListener {
        startActivity(FlutterActivity.createDefaultIntent(this));
    }

使用路由，打开Flutter指定页面

 startFlutterInitialRoute.setOnClickListener {
        startActivity(FlutterActivity
            .withNewEngine()
            .initialRoute("secondPage")
            .build(this));
    }

使用缓存的 FlutterEngine

class MyApplication : Application() {
 lateinit var flutterEngine : FlutterEngine

 override fun onCreate() {
  super.onCreate()

  // Instantiate a FlutterEngine.
  flutterEngine = FlutterEngine(this)

  // Start executing Dart code to pre-warm the FlutterEngine.
  flutterEngine.dartExecutor.executeDartEntrypoint(
    DartExecutor.DartEntrypoint.createDefault()
  )

  // Cache the FlutterEngine to be used by FlutterActivity.
  FlutterEngineCache
    .getInstance()
    .put("my_engine_id", flutterEngine)
 }
}

根据id获取对应的缓存FlutterEngine,，缓存的FlutterEngine打开Flutter页面时，明显比withNewEngine的引擎打开Flutter页面快，但是 CachedEngineIntentBuilder没有NewEngineIntentBuilder的initialRoute("")方法

 startFlutterWithCachedEngine.setOnClickListener {
        startActivity(
            FlutterActivity
                .withCachedEngine("my_engine_id")
                .build(this)
        );
    }

Start FlutterActivity with transparency 打开有透明度的FlutterActivity#

官方例子

      startActivity(
            FlutterActivity
                .withCachedEngine("my_engine_id")
                .backgroundMode(FlutterActivity.BackgroundMode.transparent)
                .build(this)
        );

看backgroundMode定义

@NonNull
public CachedEngineIntentBuilder backgroundMode(@NonNull BackgroundMode backgroundMode) {
  this.backgroundMode = backgroundMode.name();
  return this;
}

BackgroundMode所以的 FlutterActivityLaunchConfigs 类竟然不是public的，什么情况？跑不通，先放下

package io.flutter.embedding.android;

class FlutterActivityLaunchConfigs {
  //省略无关代码
  public enum BackgroundMode {
    /** Indicates a FlutterActivity with an opaque background. This is the default. */
    opaque,
    /** Indicates a FlutterActivity with a transparent background. */
    transparent
  }

  private FlutterActivityLaunchConfigs() {}
}

向 Android 应用中添加 Flutter Fragment

FlutterFragment api的和FlutterActivity api 的差不多，都有createDefaultIntent withNewEngine withCachedEngine initialRoute之类的方法

创建一个默认启动Flutter主页的

FlutterFragment.createDefault();

打开指定Flutter路由

FlutterFragment.withNewEngine().initialRoute("secondPage").build();

使用缓存的引擎

FlutterFragment.withCachedEngine("my_engine_id")
            .build()

使用transparencyMode renderMode等

FlutterFragment
    .withNewEngine()
    .transparencyMode(FlutterView.TransparencyMode.transparent)
    .renderMode(FlutterView.RenderMode.texture)
    .initialRoute("thirdPage")
    .build();

FlutterFragment使用特殊的入口

一般是使用 main()入口，可以指定其他方法作为入口
使用有一个dart方法如下

void mySpecialEntrypoint() {
    runApp(TestEntryPoint());
}

指定mySpecialEntrypoint方法作为入口

FlutterFragment flutterFragment = FlutterFragment.withNewEngine()
    .dartEntrypoint("mySpecialEntrypoint")
    .build();

FlutterFragment的渲染模式

有两种渲染模式 SurfaceView TextureView

机器翻译文

FlutterFragment既可以使用SurfaceView来呈现它的Flutter内容，也可以使用TextureView。默认的是SurfaceView，它的性能明显优于TextureView。然而，SurfaceView不能交错在Android视图层次结构的中间。SurfaceView必须是层次结构中最下面的视图，或者是层次结构中最上面的视图。此外，在Android N之前的Android版本中，SurfaceViews不能被动画化，因为它们的布局和渲染与视图层次的其余部分不同步。如果这两个用例是你的应用程序的需求，那么你需要使用TextureView而不是SurfaceView。通过使用纹理渲染模式构建一个FlutterFragment来选择一个TextureView

// With a new FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withNewEngine()
    .renderMode(FlutterView.RenderMode.texture)
    .build();

// With a cached FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withCachedEngine("my_engine_id")
    .renderMode(FlutterView.RenderMode.texture)
    .build();

显示一个有透明度的FlutterFragment

默认情况下，FlutterFragment使用SurfaceView呈现不透明的背景。(参见Control FlutterFragment s渲染模式。)对于任何不是由Flutter绘制的像素，该背景都是黑色的。出于性能考虑，使用不透明背景进行呈现是首选的呈现模式。Android上带有透明度的Flutter渲染会对性能产生负面影响。然而，有许多设计需要在Flutter体验中通过底层Android UI显示透明像素。由于这个原因，Flutter在一个FlutterFragment中支持半透明。

备忘

SurfaceView和TextureView支持透明度。然而，当一个SurfaceView被指示使用透明渲染时，它会将自己定位在一个比所有其他Android视图更高的z索引上，这意味着它会出现在所有其他视图之上。这是SurfaceView的一个限制。如果可以在所有其他内容之上呈现Flutter体验，那么FlutterFragment的默认surface渲染模式就是您应该使用的渲染模式。然而，如果你需要在你的Flutter体验上面和下面显示Android视图，那么你必须指定一个纹理渲染模式。有关控制渲染模式的信息，请参阅 FlutterFragment的渲染模式。

开启透明度

// Using a new FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withNewEngine()
    .transparencyMode(FlutterView.TransparencyMode.transparent)
    .build();

// Using a cached FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withCachedEngine("my_engine_id")
    .transparencyMode(FlutterView.TransparencyMode.transparent)
    .build();

shouldAttachEngineToActivity

将false传递给shouldAttachEngineToActivity()构造器方法可以防止Flutter与周围的Activity进行交互。默认值为true，允许Flutter和Flutter插件与周围的Activity交互。

Some plugins may expect or require an Activity reference. Ensure that none of your plugins require an Activity before you disable access.

// Using a new FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withNewEngine()
    .shouldAttachEngineToActivity(false)
    .build();

// Using a cached FlutterEngine.
FlutterFragment flutterFragment = FlutterFragment.withCachedEngine("my_engine_id")
    .shouldAttachEngineToActivity(false)
    .build();

解决FlutterActivity页面打开时白屏或黑屏的问题

启动页

如果启动页继承的是FlutterActivity,先定义一个style

<style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
    <item name="android:windowBackground">@mipmap/normal_background</item>
</style>

然后添加到AndroidManifest.xml的启动页Activity下

<activity android:name=".FlutterLauncherActivity">
    <meta-data
            android:name="io.flutter.embedding.android.NormalTheme"
            android:resource="@style/NormalTheme" />
    <intent-filter>
        <action android:name="android.intent.action.MAIN" />

        <category android:name="android.intent.category.LAUNCHER" />
    </intent-filter>
</activity>

startActivity启动的FlutterActivity

在AndroidManifest.xml的FlutterActivity下添加

<meta-data
    android:name="io.flutter.embedding.android.SplashScreenDrawable"
    android:resource="@mipmap/normal_background" />

完整如下

    <activity
        android:name="io.flutter.embedding.android.FlutterActivity"
        android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
        android:hardwareAccelerated="true"
        android:theme="@style/MyTheme"
        android:windowSoftInputMode="adjustResize">
        <meta-data
            android:name="io.flutter.embedding.android.SplashScreenDrawable"
            android:resource="@mipmap/normal_background" />
    </activity>

启动时就会先显示过渡的图片，而不会白屏或者黑屏

FlutterFragment添加过渡图片

官方指导文档就重写provideSplashScreen方法即可，SplashScreen可以自定义，显示Android View

public class MyFlutterFragment extends FlutterFragment {
    @Override
    protected SplashScreen provideSplashScreen() {
        // Load the splash Drawable.
        Drawable splash = getResources().getDrawable(R.drawable.my_splash);

        // Construct a DrawableSplashScreen with the loaded splash Drawable and
        // return it.
        return new DrawableSplashScreen(splash);
    }
}

但是FlutterFragment如果要重写,还有getActivity getContext getLifecycle三个方法要重写，这里又遇到了androidx的问题，重写失败，先放下。

 override fun getActivity(): Activity? {
    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
}

override fun getContext(): Context {
    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
}

override fun getLifecycle(): android.arch.lifecycle.Lifecycle {
    TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
}