FlutterAndroid启动源码分析（一）

前言

版本&＃xff1a;Flutter 1.20.4 stable

这个系列主要讲解在Flutter的项目中&＃xff0c;Android 从启动到加载Flutter等一系列的过程。

本文主要是对FlutterApplication的startInitialization方法及FlutterActivity整个类源码的分析

Application

android:name&＃61;"io.flutter.app.FlutterApplication"
android:label&＃61;"flutter_channel"
android:icon&＃61;"&＃64;mipmap/ic_launcher">

public class FlutterApplication extends Application {
&＃64;Override
&＃64;CallSuper
public void onCreate() {
super.onCreate();
FlutterMain.startInitialization(this);
}
}


在Android项目的AndroidManifest.xml中指定了application为FlutterApplication&＃xff0c;主要是一个初始化操作

最终会调用FlutterLoader类中的startInitialization方法

public void startInitialization(&＃64;NonNull Context applicationContext, &＃64;NonNull Settings settings) {
if (this.settings !&＃61; null) {
return;
}
if (Looper.myLooper() !&＃61; Looper.getMainLooper()) {
throw new IllegalStateException("startInitialization must be called on the main thread");
}
applicationContext &＃61; applicationContext.getApplicationContext();
this.settings &＃61; settings;
long initStartTimestampMillis &＃61; SystemClock.uptimeMillis();
initConfig(applicationContext);
initResources(applicationContext);
System.loadLibrary("flutter");
VsyncWaiter.getInstance(
(WindowManager) applicationContext.getSystemService(Context.WINDOW_SERVICE))
.init();
long initTimeMillis &＃61; SystemClock.uptimeMillis() - initStartTimestampMillis;
FlutterJNI.nativeRecordStartTimestamp(initTimeMillis);
}


• 加载Flutter引擎的本机库以启用后续的JNI调用
• 开始定位和打开应用程序APK中打包的Dart资源

FlutterApplication不 做过多分析&＃xff0c;就是一些资源的初始化和so库加载的一些操作

FlutterActivity

class MainActivity : FlutterActivity(){}


public class FlutterActivity extends Activity
implements FlutterActivityAndFragmentDelegate.Host, LifecycleOwner {

public FlutterActivity() {
lifecycle &＃61; new LifecycleRegistry(this);
}


它是继承Activity并实现了FlutterActivityAndFragmentDelegate这个代理类中的Host接口及获取生命周期的LifecycleOwner接口

构造函数里实例化了一个LifecycleRegistry&＃xff0c;它继承Lifecycle

public class LifecycleRegistry extends Lifecycle


然后实现LifecycleOwner接口的getLifecycle方法&＃xff0c;返回了LifecycleRegistry对象&＃xff0c;用于生命周期状态的监听和通知&＃xff0c;这个不用过多介绍

&＃64;Override
&＃64;NonNull
public Lifecycle getLifecycle() {
return lifecycle;
}


onCreate方法

&＃64;Override
protected void onCreate(&＃64;Nullable Bundle savedInstanceState) {
switchLaunchThemeForNormalTheme();
super.onCreate(savedInstanceState);
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_CREATE);
delegate &＃61; new FlutterActivityAndFragmentDelegate(this);
delegate.onAttach(this);
delegate.onActivityCreated(savedInstanceState);
configureWindowForTransparency();
setContentView(createFlutterView());
configureStatusBarForFullscreenFlutterExperience();
}


&＃64;NonNull
private View createFlutterView() {
return delegate.onCreateView(
null /* inflater */, null /* container */, null /* savedInstanceState */);
}


对于主题和状态栏的设置我们不去关注&＃xff0c;重点看一下configureWindowForTransparency这个方法和对FlutterActivityAndFragmentDelegate的一些操作

configureWindowForTransparency

如果FlutterActivity背景模式是透明&＃xff08;默认是不透明的模式&＃xff09;&＃xff0c;则设置整个FlutterActivity窗口透明及隐藏状态栏

其实如果我们不在原生项目中使用FlutterModule进行混合开发的话&＃xff0c;是不需要关注这个方法的。因为默认就是非透明模式。

这里只是先提一嘴&＃xff0c;后续讲到混合开发时会涉及到这个方法的一些配置

private void configureWindowForTransparency() {
BackgroundMode backgroundMode &＃61; getBackgroundMode();
if (backgroundMode &＃61;&＃61; BackgroundMode.transparent) {
getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
}
}


FlutterActivityAndFragmentDelegate

1. 主要是实例化了FlutterActivityAndFragmentDelegate&＃xff0c;传递FlutterActivityAndFragmentDelegate.Host实现类即当前类this
2. 调用delegate.onAttach、onActivityCreated及onCreateView方法
3. 关于FlutterActivityAndFragmentDelegate的介绍&＃xff0c;我们放到下一篇文章里

其他生命周期方法大同小异&＃xff0c;基本都是通过LifecycleRegistry.handleLifecycleEvent设置当前界面状态。然后将当前生命周期委托给delegate进行操作

&＃64;Override
protected void onStart() {
super.onStart();
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_START);
delegate.onStart();
}
&＃64;Override
protected void onResume() {
super.onResume();
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_RESUME);
delegate.onResume();
}
&＃64;Override
public void onPostResume() {
super.onPostResume();
delegate.onPostResume();
}
&＃64;Override
protected void onPause() {
super.onPause();
delegate.onPause();
lifecycle.handleLifecycleEvent(Lifecycle.Event.ON_PAUSE);
}


接下来就是一些重写FlutterActivityAndFragmentDelegate.Host接口的方法

/* package */ interface Host
extends SplashScreenProvider, FlutterEngineProvider, FlutterEngineConfigurator {


我们先看一下这个Host接口具体有哪些方法

下面根据其用途进行了一个大致的分类

• 获取Context、Activity、Lifecycle

  
  

  方法名	描述
  Context getContext();	获取上下文对象
  Activity getActivity();	获取activity对象
  Lifecycle getLifecycle();	获取Lifecycle&＃xff0c;返回的就是上面说的LifecycleRegistry

• 实例化FlutterEngine

  
  

  方法名	描述
  String getCachedEngineId();	缓存的FlutterEngine Id
  FlutterEngine provideFlutterEngine(&＃64;NonNull Context context);	提供一个FlutterEngine&＃xff0c;目前版本返回null&＃xff0c;暂不考虑
  FlutterShellArgs getFlutterShellArgs();	初始化参数
  boolean shouldAttachEngineToActivity();	建立Engine和Activity的连接关系&＃xff0c;控制界面用于向附加到 FlutterEngine的插件提供Android资源和生命周期事件。
  PlatformPlugin providePlatformPlugin( &＃64;Nullable Activity activity, &＃64;NonNull FlutterEngine flutterEngine);	提供一个PlatformPlugin&＃xff08;Android平台的插件实现&＃xff09;

• 在FlutterView里首次运行Dart所需参数

  
  

  方法名	描述
  String getAppBundlePath();	返回包含dart代码的app bundle 路径
  String getInitialRoute();	初始化路由路径
  String getDartEntrypointFunctionName();	dart代码执行入口函数名称

• 实例化FlutterSplashView&＃xff08;启动界面及整个FlutterView&＃xff09;

  
  

  方法名	描述
  RenderMode getRenderMode();	Flutter UI 渲染模式&＃xff0c;默认是surface
  TransparencyMode getTransparencyMode();	透明度模式&＃xff0c;默认是opaque
  void onFlutterSurfaceViewCreated(&＃64;NonNull FlutterSurfaceView flutterSurfaceView);	FlutterSurfaceView创建回调
  void onFlutterTextureViewCreated(&＃64;NonNull FlutterTextureView flutterTextureView);	FlutterTextureView创建回调
  void onFlutterUiDisplayed();	FlutterView首次渲染回调
  void onFlutterUiNoLongerDisplayed();	FlutterView停止渲染回调
  SplashScreen provideSplashScreen();	返回一个SplashScreen

  
  

  方法名	描述
  boolean shouldDestroyEngineWithHost();	是否清理engine

这里我们只对configureFlutterEngine方法实现做详细分析&＃xff0c;剩余的在下篇文章中具体说明

configureFlutterEngine 插件注册方法

在FlutterActivityAndFragmentDelegate.onAttach方法中进行调用

void onAttach(&＃64;NonNull Context context) {
// 省略部分代码
host.configureFlutterEngine(flutterEngine);
}


FlutterActivity对其实现如下

&＃64;Override
public void configureFlutterEngine(&＃64;NonNull FlutterEngine flutterEngine) {
registerPlugins(flutterEngine);
}
private static void registerPlugins(&＃64;NonNull FlutterEngine flutterEngine) {
try {
Class generatedPluginRegistrant &＃61;
Class.forName("io.flutter.plugins.GeneratedPluginRegistrant");
Method registrationMethod &＃61;
generatedPluginRegistrant.getDeclaredMethod("registerWith", FlutterEngine.class);
registrationMethod.invoke(null, flutterEngine);
} catch (Exception e) {
Log.w(
TAG,
"Tried to automatically register plugins with FlutterEngine ("
&＃43; flutterEngine
&＃43; ") but could not find and invoke the GeneratedPluginRegistrant.");
}
}


这里通过反射执行GeneratedPluginRegistrant.registerWith方法来注册pubspec.yaml中添加的插件依赖

&＃64;Keep
public final class GeneratedPluginRegistrant {
public static void registerWith(&＃64;NonNull FlutterEngine flutterEngine) {
flutterEngine.getPlugins().add(new com.befovy.fijkplayer.FijkPlugin());
}
}


registerWith方法中的 flutterEngine.getPlugins().add(xxx)无需我们手动添加&＃xff0c;当执行pub get 时&＃xff0c;如果含原生插件&＃xff0c;则flutter会自动去添加&＃xff0c;而且其实如果我们不注册自己的原生插件的话&＃xff0c;这个方法其实也是不需要去做任何操作的。默认都是自动注册。这个方法及其业务逻辑在最近Flutter几个版本的更新中有很大的变化

如果我们要注册自己的原生插件&＃xff0c;则需要在MainActivity中重写configureFlutterEngine并调用super.configureFlutterEngine&＃xff0c;然后通过 flutterEngine.plugins.add方法进行注册

class MainActivity : FlutterActivity() {
override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
super.configureFlutterEngine(flutterEngine)
// 原生封装的FlutterPlugin需要手动进行注册
flutterEngine.plugins.add(ToastPlugin())
}
}


总结

通过本文我们可以学习到

1. FlutterApplication主要做了哪些工作
2. MainActivity继承的FlutterActivity主要做了哪些工作

以上内容如有不准确的地方&＃xff0c;麻烦大家在评论区指出&＃xff0c;我会一一改正

下篇文章会分析FlutterActivityAndFragmentDelegate这个代理类的一些逻辑&＃xff0c;这个类比较关键&＃xff0c;它是主要负责FlutterActivity和FlutterEngine、FlutterView、PlatformPlugin等一些联动工作&＃xff0c;比如Engine注册、Dart执行、平台插件实现以及Activity和Engine生命周期的一些控制等等&＃xff0c;同时会衍生出很多类。可以说这篇文章只是一个起点&＃xff0c;核心业务在后面。

本文地址：https://blog.csdn.net/fighting_android/article/details/108700276