Flutter核心原理（Flutter启动流程和渲染管线 ）

应用启动

Flutter的入口在"lib/main.dart"的main()函数中，它是Dart应用程序的起点。

void main() => runApp(MyApp());

查看runApp()方法

void runApp(Widget app) {
   
  WidgetsFlutterBinding.ensureInitialized()
    ..scheduleAttachRootWidget(app)
    ..scheduleWarmUpFrame();
}

app是第一个组件，WidgetsFlutterBinding是绑定widget和Flutter引擎的桥梁。

WidgetsFlutterBinding

class WidgetsFlutterBinding extends BindingBase with GestureBinding, ServicesBinding, SchedulerBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {
   
  static WidgetsBinding ensureInitialized() {
   
    if (WidgetsBinding.instance == null)
      WidgetsFlutterBinding();
    return WidgetsBinding.instance;
  }
}

WidgetsFlutterBinding继承BindingBase，并且引入很多Binding，通过各种Binding源码可以看出基本上都是监听并处理Window对象的一些事件。WidgetsFlutterBinding.ensureInitialized()负责初始化一个WidgetsBinding的全局单例，然后调用scheduleAttachRootWidget方法将根Widget添加到RenderView。

attachRootWidget

void scheduleAttachRootWidget(Widget rootWidget) {
   
    Timer.run((