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了解了Flutter的Widget以及Flutter的渲染，突然有新的问题的产生，Flutter如果要和Native进行混合开发，就会产生新的问题，

混合栈管理
比如Flutter要回退到原生界面，原生界面应该如何感知呢，原生界面进入Flutter界面又要怎么通知Native

根据源码加图片来看下Flutter怎么在Android启动

Flutter出现的目的旨在统一Android/IOS两端编程，因此完全基于Flutter开发的App，只需提供一个包含FlutterView的页面，后续页面增加/删除/跳转均在FlutterView的Navigator中进行管理。

直接公布最合适的方案

<img src=”./pics/3.png” width=400” height=”300” />

抽取单一FlutterView或FlutterNativeView，后续每启动一个Activity都对FlutterView或FlutterNativeView进行复用

对比RN，native与rn混合开发，是有一个reactActivity，用layoutInspector看下Flutter层面

可以看到flutter基于自身去渲染

接下来用源码看戏FlutterActivity都做了什么操作

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public class FlutterActivity extends Activity implements Provider, PluginRegistry, ViewFactory {
    private final FlutterActivityDelegate delegate = new FlutterActivityDelegate(this, this);//1
    private final FlutterActivityEvents eventDelegate;//1
    private final Provider viewProvider;
    private final PluginRegistry pluginRegistry;//2

    public FlutterActivity() {
        this.eventDelegate = this.delegate;
        this.viewProvider = this.delegate;
        this.pluginRegistry = this.delegate;
    }
    …………
}

看下构造函数

2.pluginRegistry主要用于原生方法注册通信的，封装一些方法，相当于给Flutter增加插件

1.FlutterActivityEvents是一个接口，具体实现类是FlutterActivityDelegate 给FlutterView发送当前app处于的状态，包括内存和生命周期，上下文，以及intent

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   protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        this.eventDelegate.onCreate(savedInstanceState);
    }
  public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        this.eventDelegate.onConfigurationChanged(newConfig);
    }

  protected void onPostResume() {
        super.onPostResume();
        this.eventDelegate.onPostResume();
    }
…………

1.我们知道当走到Activity的onCreate时，会执行Delegate的onCreate

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public FlutterActivityDelegate(Activity activity, FlutterActivityDelegate.ViewFactory viewFactory) {
    this.activity = (Activity)Preconditions.checkNotNull(activity);
    this.viewFactory = (FlutterActivityDelegate.ViewFactory)Preconditions.checkNotNull(viewFactory);
}


public void onCreate(Bundle savedInstanceState) {
    if (VERSION.SDK_INT >= 21) {
        Window window = this.activity.getWindow();
        window.addFlags(-2147483648);
        window.setStatusBarColor(1073741824);
        window.getDecorView().setSystemUiVisibility(1280);
    }

    String[] args = getArgsFromIntent(this.activity.getIntent());
    FlutterMain.ensureInitializationComplete(this.activity.getApplicationContext(), args);
    this.flutterView = this.viewFactory.createFlutterView(this.activity);
    if (this.flutterView == null) {
        FlutterNativeView nativeView = this.viewFactory.createFlutterNativeView();
        this.flutterView = new FlutterView(this.activity, (AttributeSet)null, nativeView);
        this.flutterView.setLayoutParams(matchParent);
        this.activity.setContentView(this.flutterView);//1
        this.launchView = this.createLaunchView();
        if (this.launchView != null) {
            this.addLaunchView();
        }
    }

1.通过setContentView 将Flutter视图放入window中

看下flutterView

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public class FlutterView extends SurfaceView implements BinaryMessenger, TextureRegistry, AccessibilityStateChangeListener {
}

主要是做了native定位、生命周期、以及获取原生一些信息的通道。