上篇文章我们介绍了如何将Flutter模块混入iOS项目中，本篇文章我们来介绍下Android项目混入Flutter模块的方法。
建议先阅读一下Flutter混合开发—iOS篇，本文中提到的一些与iOS篇中相同的内容就不会再介绍了。
现在就进入Flutter和Android进行混合开发的实现过程。
搭建Android项目
首先我们搭建一个首页为Bottom Navigation Activity的安卓项目，然后修改代码将三个Fragment重命名为HomeFragment，ChannelFragment和MineFragment。
项目
fragment_home.xml
<?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"
android:background="#2196F3"
tools:context=".ui.home.HomeFragment">
// 这个FrameLayout会被用来显示Flutter Module内容
<FrameLayout
android:id="@+id/main_fl"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="56dp"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
搭建完成后，App的效果如下图所示：
效果图
我们接下来的工作是把Flutter的MainApp(),ChannelApp()和MineApp()分别加入到上面提到的三个Fragment中。
Android项目引入Flutter Module
首先确保Android Studio安装了Flutter plugin(安装Flutter插件的过程略过)
使用 File > New > Import Module ... -> 选择flutter module ，然后指定一个module name
新建Module
- 填写相应的信息
信息
图中有一个警告，是因为我第一操作的时候没有截图，第二次重复操作的警告。
- 点击确定，等待
Gradle sync完成
Android项目集成Flutter Module
创建一个FlutterEngineGroup对象
FlutterEngineGroup可以用来管理多个FlutterEngine对象，多个FlutterEngine之间是可以共享资源的，这样建立多个FlutterEngine占用的资源相对会少一下。
FBApplication.kt
class FBApplication: Application() {
lateinit var engineGroup: FlutterEngineGroup
override fun onCreate() {
super.onCreate()
// 创建FlutterEngineGroup对象
engineGroup = FlutterEngineGroup(this)
}
}
AndroidManifest.xml
<application
android:name=".FBApplication"
// 省略...
>
<activity
android:name=".MainActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
创建一个FBFlutterEngineManager缓存管理类
我们在FBFlutterEngineManager中创建一个静态方法flutterEngine:
object FBFlutterEngineManager {
fun flutterEngine(context: Context, engineId: String, entryPoint: String): FlutterEngine {
// 1. 从缓存中获取FlutterEngine
var engine = FlutterEngineCache.getInstance().get(engineId)
if (engine == null) {
// 如果缓存中没有FlutterEngine
// 1. 新建FlutterEngine，执行的入口函数是entryPoint
val app = context.applicationContext as FBApplication
val dartEntrypoint = DartExecutor.DartEntrypoint(FlutterInjector.instance().flutterLoader().findAppBundlePath(), entryPoint)
engine = app.engineGroup.createAndRunEngine(context, dartEntrypoint)
// 2. 存入缓存
FlutterEngineCache.getInstance().put(engineId, engine)
}
return engine!!
}
}
这里我们使用了
FlutterEngineCache缓存类，先从中获取缓存的FlutterEngine，如果没有取到，则新建一个FlutterEngine，然后缓存起来。
Fragment中嵌入Flutter Module
我们这一步是将FlutterEngine和FlutterFragment进行绑定，然后显示。
class HomeFragment : Fragment() {
// 1. FlutterEngine对象
private lateinit var engine: FlutterEngine
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_home, container, false)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
// 2. 通过FBFlutterEngineManager获取FlutterEngine对象
engine = FBFlutterEngineManager.flutterEngine(requireActivity(), R.id.main_fl.toString(), "main")
// 3. 用FlutterEngine对象构建出一个FlutterFragment
val flutterFragment = FlutterFragment.withCachedEngine(R.id.main_fl.toString()).build<FlutterFragment>()
// 4. 显示FlutterFragment
parentFragmentManager.beginTransaction().replace(R.id.main_fl, flutterFragment).commit()
}
}
我们这里使用缓存的FlutterEngine更能节省资源，因为Bottom Navigation Activity的Fragment来回切换的时候，Fragment是会重新新建和销毁的。
下面就是实现的效果图：
效果图
编写插件代码
和iOS类似，我们需要在进入将二级页面时候，将activity_main.xml中的BottomNavigationView隐藏，回到一级页面的时候将BottomNavigationView显示出来。
- 添加显示和隐藏的方法
class MainActivity : AppCompatActivity() {
fun switchBottomView(show: Boolean) {
val navView: BottomNavigationView = findViewById(R.id.nav_view)
if (show) {
navView.visibility = View.VISIBLE
} else {
navView.visibility = View.GONE
}
}
}
- MethodChannel 注册回调
var channel: MethodChannel = MethodChannel(engine.dartExecutor.binaryMessenger, "fbmovie.com/tab_switch")
channel.setMethodCallHandler { call, result ->
when (call.method) {
"showTab" -> {
val activity = requireActivity() as MainActivity
activity.switchBottomView(true)
result.success(null)
}
"hideTab" -> {
val activity = requireActivity() as MainActivity
activity.switchBottomView(false)
result.success(null)
}
else -> {
result.notImplemented()
}
}
}
代码
FBApplication.kt
class FBApplication: Application() {
lateinit var engineGroup: FlutterEngineGroup
override fun onCreate() {
super.onCreate()
engineGroup = FlutterEngineGroup(this)
}
}
FBFlutterEngineManager.kt
object FBFlutterEngineManager {
fun flutterEngine(context: Context, engineId: String, entryPoint: String): FlutterEngine {
var engine = FlutterEngineCache.getInstance().get(engineId)
if (engine == null) { //如果是空的就新建，然后存起来
val app = context.applicationContext as FBApplication
val dartEntrypoint = DartExecutor.DartEntrypoint(FlutterInjector.instance().flutterLoader().findAppBundlePath(), entryPoint)
engine = app.engineGroup.createAndRunEngine(context, dartEntrypoint)
FlutterEngineCache.getInstance().put(engineId, engine)
}
return engine!!
}
}
MainActivity.kt
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
// 修改状态栏颜色
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
window.decorView.systemUiVisibility = View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR
}
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val navView: BottomNavigationView = findViewById(R.id.nav_view)
val navController = findNavController(R.id.nav_host_fragment)
navView.setupWithNavController(navController)
}
fun switchBottomView(show: Boolean) {
val navView: BottomNavigationView = findViewById(R.id.nav_view)
if (show) {
navView.visibility = View.VISIBLE
} else {
navView.visibility = View.GONE
}
}
}
HomeFragment.kt
class HomeFragment : Fragment() {
private lateinit var engine: FlutterEngine
private lateinit var channel: MethodChannel
override fun onCreateView(
inflater: LayoutInflater,
container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
return inflater.inflate(R.layout.fragment_home, container, false)
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
engine = FBFlutterEngineManager.flutterEngine(requireActivity(), R.id.main_fl.toString(), "main")
val flutterFragment = FlutterFragment.withCachedEngine(R.id.main_fl.toString()).build<FlutterFragment>()
parentFragmentManager.beginTransaction().replace(R.id.main_fl, flutterFragment).commit()
channel = MethodChannel(engine.dartExecutor.binaryMessenger, "fbmovie.com/tab_switch")
channel.setMethodCallHandler { call, result ->
when (call.method) {
"showTab" -> {
val activity = requireActivity() as MainActivity
activity.switchBottomView(true)
result.success(null)
}
"hideTab" -> {
val activity = requireActivity() as MainActivity
activity.switchBottomView(false)
result.success(null)
}
else -> {
result.notImplemented()
}
}
}
}
}
总结
目前原生移动应用能集成多个Flutter Module，这样使用起来就方便多了。
Android中也可以使用FlutterView, 在一个Activity或者Fragment中可以展示多个FlutterView，但是使用个FlutterView需要绑定生命周期，使用起来稍显复杂。
