FlutterBoost源码解析

项目中在使用FlutterBoost，对其实现原理比较好奇，看了一下，关键的类有点多，自己捋一捋，记录一下，便于理解

FlutterBoost解决的混合开发过程中的几个痛点：

统一了native和flutter之间跳转方式
提供与native一致的生命周期管理
优化FlutterEngine的使用，减少内存消耗
其他（比如黑屏闪屏的坑）

关系详解：todo

主要的结构图

image.png

关键类的作用 todo
关键类的层级关系

image.png

flutter跳转native过程比较简单清晰，下面分析下flutter跳转flutter的整个流程

跳转入口

 FlutterBoost.singleton.open(RouterConstants.USER_INFO_PAGE);

看一下open做了什么

Future<Map<dynamic, dynamic>> open(String url,
     {Map<dynamic, dynamic> urlParams, Map<dynamic, dynamic> exts}) {
   Map<dynamic, dynamic> properties = new Map<dynamic, dynamic>();
   properties["url"] = url;
   properties["urlParams"] = urlParams;
   properties["exts"] = exts;
   return channel.invokeMethod<Map<dynamic, dynamic>>('openPage', properties);
 }

调用了BoostChannel（点进去发现是对MethodChannel的一个包装）的invokeMethod方法，最终是调用的MethodChannel的invokeMethod，指向的’openPage‘

  Future<T> invokeMethod<T>(String method, [dynamic arguments]) async {
    assert(method != "__event__");

    return _methodChannel.invokeMethod<T>(method, arguments);
  }

找一下native那边对应的注册位置，FlutterBoostPlugin$BoostMethodHandler

 class BoostMethodHandler implements MethodChannel.MethodCallHandler {

        @Override
        public void onMethodCall(MethodCall methodCall, final MethodChannel.Result result) {

            FlutterViewContainerManager mManager = (FlutterViewContainerManager) FlutterBoost.instance().containerManager();
            switch (methodCall.method) {
               ...
                case "openPage": {
                    try {
                        Map<String, Object> params = methodCall.argument("urlParams");
                        Map<String, Object> exts = methodCall.argument("exts");
                        String url = methodCall.argument("url");

                        mManager.openContainer(url, params, exts, new FlutterViewContainerManager.OnResult() {
                            @Override
                            public void onResult(Map<String, Object> rlt) {
                                if (result != null) {
                                    result.success(rlt);
                                }
                            }
                        });
                    } catch (Throwable t) {
                        result.error("open page error", t.getMessage(), Log.getStackTraceString(t));
                    }
                }
                break;
               ...
                default: {
                    result.notImplemented();
                }
            }
        }
    }

来到FlutterViewContainerManager里的OpenContainer方法

 void openContainer(String url, Map<String, Object> urlParams, Map<String, Object> exts,OnResult onResult) {
      ...
       FlutterBoost.instance().platform().openContainer(context,url,urlParams,requestCode,exts);
    }

调用的是Platform类的openContainer，其实现在Flutterboost的build方法中

 public Platform build() {

            Platform platform = new Platform() {
                public void openContainer(Context context, String url, Map<String, Object> urlParams, int requestCode, Map<String, Object> exts) {
                    router.openContainer(context, url, urlParams, requestCode, exts);
                }

        }

最终调用到router对象的OpenContainer，而这个router具体实现，则在我们构造Platform对象时生成的

INativeRouter router = (context, url, urlParams, requestCode, exts) -> {
            String assembleUrl = Utils.assembleUrl(url, urlParams);
            PageRouter.openPageByUrl(context, assembleUrl, urlParams);
        };

继续往下看，openPagerByUrl方法，通过BoostFlutterActivity的一系列构造，生成了一个intent

   Intent intent = BoostFlutterActivity
                        .withNewEngine()
                        .url(pageName.get(path))
                        .params(params)
                        .backgroundMode(BoostFlutterActivity.BackgroundMode.opaque)
                        .build(context);

而这个intent指向的目标Activity其实就是BoostFlutterActivity，在调用withNewEngine时赋值

SerializableMap serializableMap = new SerializableMap();
            serializableMap.setMap(params);

            return new Intent(context, activityClass)
                    .putExtra(EXTRA_BACKGROUND_MODE, backgroundMode)
                    .putExtra(EXTRA_DESTROY_ENGINE_WITH_ACTIVITY, false)
                    .putExtra(EXTRA_URL, url)
                    .putExtra(EXTRA_PARAMS, serializableMap);




    public static NewEngineIntentBuilder withNewEngine() {
        return new NewEngineIntentBuilder(BoostFlutterActivity.class);
    }

ContainerCoordinator
接下来ContainerRecord中的MethodChannelProxy是关键

那么，intent里面配置的这些关键参数在哪里使用到了呢？看看FlutterActivityAndFragmentDeleg
ate里的onCreateView方法中调用的syncer关键类，从名字和里面的内容可以看得出，它的作用主要用来做生命周期同步的

public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
      ...
      mSyncer.onCreate();
      return flutterSplashView;
  }

具体实现在ContainerRecord的onCreate中，并且运用了一个代理模式，最终调用到了这一个方法

 private void create() {
            if (mState == STATE_UNKNOW) {
                invokeChannelUnsafe("didInitPageContainer",
                        mContainer.getContainerUrl(),
                        mContainer.getContainerUrlParams(),
                        mUniqueId
                );
                //Debuger.log("didInitPageContainer");
                mState = STATE_CREATED;
            }
        }

继续往下深入几层，可以看到注册了一个名为“flutter_booost”的MethodChannel，将方法名和参数传到了这里

mMethodChannel = new MethodChannel(registrar.messenger(), "flutter_boost");

那么在Dart端，是在哪里接收的呢？我们查一下flutter里注册的channel，发现果然存在一个BoostChannel

class BoostChannel {
  final MethodChannel _methodChannel = MethodChannel("flutter_boost");

  final Map<String, List<EventListener>> _eventListeners = Map();
  final Set<MethodHandler> _methodHandlers = Set();

  BoostChannel() {
    _methodChannel.setMethodCallHandler((MethodCall call) {
      if (call.method == "__event__") {
        String name = call.arguments["name"];
        Map arg = call.arguments["arguments"];
        List<EventListener> list = _eventListeners[name];
        if (list != null) {
          for (EventListener l in list) {
            l(name, arg);
          }
        }
      } else {
        for (MethodHandler handler in _methodHandlers) {
          handler(call);
        }
      }

      return Future<dynamic>.value();
    });
  }
}

由于方法名称是didInitPageContainer，所以走的else分支，再继续往下走，可以看到另外一个关键类：ContainerCoordinator ，里面注册了了很多方法回调，包括我们要找的didInitPageContainer


  Future<dynamic> _onMethodCall(MethodCall call) {
    Logger.log("onMetohdCall ${call.method}");

    switch (call.method) {
      case "didInitPageContainer":
        {
          String pageName = call.arguments["pageName"];
          Map params = call.arguments["params"];
          String uniqueId = call.arguments["uniqueId"];
          _nativeContainerDidInit(pageName, params, uniqueId);
        }
        break;
        ...
    }

    return Future<dynamic>(() {});
  }

这里面有个关键方法_nativeContainerDidInit，

bool _nativeContainerDidInit(String name, Map params, String pageId) {
    performContainerLifeCycle(_createContainerSettings(name, params, pageId),
        ContainerLifeCycle.Init);
    return true;
  }

然后就在_pageBuilders里去找，有没有name对应的pageBuilder

 BoostContainerSettings _createContainerSettings(
      String name, Map params, String pageId) {
    Widget page;

    final BoostContainerSettings routeSettings = BoostContainerSettings(
        uniqueId: pageId,
        name: name,
        params: params,
        builder: (BuildContext ctx) {
          //Try to build a page using keyed builder.
          if (_pageBuilders[name] != null) {
            page = _pageBuilders[name](name, params, pageId);
          }

          //Build a page using default builder.
          if (page == null && _defaultPageBuilder != null) {
            page = _defaultPageBuilder(name, params, pageId);
          }

          assert(page != null);
          Logger.log('build widget:$page for page:$name($pageId)');

          return page;
        });

    return routeSettings;
  }

那么，这个pageBuilders又是什么，何时赋值的呢？我们再回头看看dart端flutter_boost路由注册的地方

 ///Register a map builders
  void registerPageBuilders(Map<String, PageBuilder> builders) {
    ContainerCoordinator.singleton.registerPageBuilders(builders);
  }

这个我们一般在dart的main.dart里初始化

FlutterBoost.singleton.registerPageBuilders({
    RouterConstants.MINE_PAGE: (pageName, params, _) {
      return MinePage(params);
    },
    RouterConstants.USER_INFO_PAGE: (pageName, params, _) {
      return UserInfoPage(params);
    }
  });

这样，flutter跳转flutter页面的主体流程就走完了，思路也更清晰了一些