一 概述

• Android原生开发中，Fragment可以作为Activity页面的一部分(Activity的一部分或者ViewPager的一个页面)
• Flutter可以作为FlutterFragment集成到原生页面中呈现

二 FlutterFragment开发的一般步骤

• 初始化Flutter路由
• 设置Dart执行入口
• 背景是否透明
• 使用是否FlutterEngine或者带缓存的FlutterEngine

三 界面布局(activity与Fragment的关系)

3.1 界面(TextView+RelativeLayout)

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Activity原生页面"
        android:textSize="20dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <RelativeLayout
        android:id="@+id/fragment_container"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

3.2 将activity中的一部分替换为Fragment

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

说明：将相对布局替换为Fragment显示

四 不使用带缓存的FlutterEngine和路由

4.1 代码

class MainActivity : AppCompatActivity() {
    private val TAG_FLUTTER_FRAGMENT = "flutter_fragment"
    private var flutterFragment: FlutterFragment? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       val fragmentManager: FragmentManager = supportFragmentManager
        flutterFragment = fragmentManager
            .findFragmentByTag(TAG_FLUTTER_FRAGMENT) as FlutterFragment?
        if (flutterFragment == null) {
            flutterFragment = FlutterFragment.createDefault();
            fragmentManager
                .beginTransaction()
                .add(
                    R.id.fragment_container,
                    flutterFragment!!,
                    TAG_FLUTTER_FRAGMENT
                )
                .commit();
        }
    }

    override fun onPostResume() {
        super.onPostResume()
        //flutterFragment?.onPostResume()
    }

    override fun onNewIntent(intent: Intent) {
        super.onNewIntent(intent)
           flutterFragment?.onNewIntent(intent)
    }

    override fun onBackPressed() {
        super.onBackPressed()
        flutterFragment?.onBackPressed()
    }

    override fun onRequestPermissionsResult(
        requestCode: Int,
        permissions: Array<out String>,
        grantResults: IntArray
    ) {
        flutterFragment?.onRequestPermissionsResult(requestCode, permissions, grantResults)
    }

    override fun onUserLeaveHint() {
        super.onUserLeaveHint()
        flutterFragment?.onUserLeaveHint()
    }

    override fun onTrimMemory(level: Int) {
        super.onTrimMemory(level)
        flutterFragment?.onTrimMemory(level)
    }
}

4.2 效果图

五 使用带缓存不带路由的Fragment

5.1 代码

MyApplication

public class MyApplication extends Application {
    public FlutterEngine flutterEngine;

    @Override
    public void onCreate() {
        super.onCreate();
        // Instantiate a FlutterEngine.
        flutterEngine = new FlutterEngine(this);
        // Start executing Dart code to pre-warm the FlutterEngine.
        flutterEngine.getDartExecutor().executeDartEntrypoint(
                DartExecutor.DartEntrypoint.createDefault()
        );
        // Cache the FlutterEngine to be used by FlutterActivity.
        FlutterEngineCache
                .getInstance()
                .put("my_engine_id", flutterEngine);
    }
}

MainActivity

class MainActivity : AppCompatActivity() {
    private val TAG_FLUTTER_FRAGMENT = "flutter_fragment"
    private var flutterFragment: FlutterFragment? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       val fragmentManager: FragmentManager = supportFragmentManager
        flutterFragment = fragmentManager
            .findFragmentByTag(TAG_FLUTTER_FRAGMENT) as FlutterFragment?
        if (flutterFragment == null) {     
            flutterFragment=  FlutterFragment.withCachedEngine("my_engine_id").build()
            fragmentManager
                .beginTransaction()
                .add(
                    R.id.fragment_container,
                    flutterFragment!!,
                    TAG_FLUTTER_FRAGMENT
                )
                .commit();
        }
    }
}    

5.2 效果图

六 既带缓存又有路由(b页面)的Fragment

6.1 代码

MyApplication

public class MyApplication extends Application {
    public FlutterEngine flutterEngine;

    @Override
    public void onCreate() {
        super.onCreate();
        // Instantiate a FlutterEngine.
        flutterEngine = new FlutterEngine(this);
        flutterEngine.getNavigationChannel().setInitialRoute("/b");
        // Start executing Dart code to pre-warm the FlutterEngine.
        flutterEngine.getDartExecutor().executeDartEntrypoint(
                DartExecutor.DartEntrypoint.createDefault()
        );
        // Cache the FlutterEngine to be used by FlutterActivity.
        FlutterEngineCache
                .getInstance()
                .put("my_engine_id", flutterEngine);
    }
}

MainActivity

class MainActivity : AppCompatActivity() {
    private val TAG_FLUTTER_FRAGMENT = "flutter_fragment"
    private var flutterFragment: FlutterFragment? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
       val fragmentManager: FragmentManager = supportFragmentManager
        flutterFragment = fragmentManager
            .findFragmentByTag(TAG_FLUTTER_FRAGMENT) as FlutterFragment?
        if (flutterFragment == null) {
            flutterFragment=FlutterFragment.withNewEngine().initialRoute("/b").build()
            fragmentManager
                .beginTransaction()
                .add(
                    R.id.fragment_container,
                    flutterFragment!!,
                    TAG_FLUTTER_FRAGMENT
                )
                .commit();
        }
    }
}

6.2 效果图

七 参考

• Flutter官方文档-Adding a Flutter Fragment to an Android app