原有Android项目中体验Flutter

android {
  //...
  defaultConfig {
    ndk {
      // Filter for architectures supported by Flutter.
      // 如果使用Android模拟器测试请添加'x86'平台
      abiFilters 'armeabi-v7a', 'arm64-v8a', 'x86_64'
    }
  }
}

android {
  //...
  compileOptions {
    sourceCompatibility 1.8
    targetCompatibility 1.8
  }
}

// Include the host app project.
include ':app'                                    // assumed existing content
setBinding(new Binding([gradle: this]))                                // new
evaluate(new File(                                                     // new
  settingsDir.parentFile,                                              // new
  'my_flutter/.android/include_flutter.groovy'                         // new
))                                                                     // new

dependencies {
  implementation project(':flutter')
}

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

//打开首页
startActivity(
  FlutterActivity.createDefaultIntent(currentActivity)
);

//根据路由打开指定页面
startActivity(
        FlutterActivity
                .withNewEngine()
                .initialRoute("/other")
                .build(MainActivity.this)
);

//初始化FlutterEngine并进行缓存
FlutterEngine flutterEngine = new FlutterEngine(this);
flutterEngine.getDartExecutor().executeDartEntrypoint(
        DartExecutor.DartEntrypoint.createDefault()
);
FlutterEngineCache.getInstance().put("my_engine_id", flutterEngine);

//改变启动方式
startActivity(
    FlutterActivity.withCachedEngine("my_engine_id").build(MainActivity.this);
);

在创建flutterEngine对象后插入如下内容:
flutterEngine.getNavigationChannel().setInitialRoute("/other");

<FrameLayout
    android:layout_weight="1"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

// Define a tag String to represent the FlutterFragment within this
// Activity's FragmentManager. This value can be whatever you'd like.
private static final String TAG_FLUTTER_FRAGMENT = "flutter_fragment";

// Declare a local variable to reference the FlutterFragment so that you
// can forward calls to it later.
private FlutterFragment flutterFragment;

// Get a reference to the Activity's FragmentManager to add a new
    // FlutterFragment, or find an existing one.
    FragmentManager fragmentManager = getSupportFragmentManager();

    // Attempt to find an existing FlutterFragment,
    // in case this is not the first time that onCreate() was run.
    flutterFragment = (FlutterFragment) fragmentManager
            .findFragmentByTag(TAG_FLUTTER_FRAGMENT);

    // Create and attach a FlutterFragment if one does not exist.
    if (flutterFragment == null) {
        flutterFragment = FlutterFragment.createDefault();

        fragmentManager
                .beginTransaction()
                .add(
                        R.id.fragment_container,
                        flutterFragment,
                        TAG_FLUTTER_FRAGMENT
                )
                .commit();
    }

@Override
public void onPostResume() {
    super.onPostResume();
    flutterFragment.onPostResume();
}

@Override
protected void onNewIntent(@NonNull Intent intent) {
    super.onNewIntent(intent);
    flutterFragment.onNewIntent(intent);
}

@Override
public void onBackPressed() {
    flutterFragment.onBackPressed();
}

@Override
public void onRequestPermissionsResult(
        int requestCode,
        @NonNull String[] permissions,
        @NonNull int[] grantResults
) {
    flutterFragment.onRequestPermissionsResult(
            requestCode,
            permissions,
            grantResults
    );
}

@Override
public void onUserLeaveHint() {
    flutterFragment.onUserLeaveHint();
}

@Override
public void onTrimMemory(int level) {
    super.onTrimMemory(level);
    flutterFragment.onTrimMemory(level);
}

if (flutterFragment == null) {
    flutterFragment = FlutterFragment.withCachedEngine("my_engine_id").build();
    fragmentManager
            .beginTransaction()
            .add(
                    R.id.fragment_container,
                    flutterFragment,
                    TAG_FLUTTER_FRAGMENT
            )
            .commit();
}