任何应用程序都是从main()开始的，Flutter也不例外。Flutter 的启动入口在 lib/main.dart 里的 main() 函数中，代码如下。

void main() => runApp(MyApp());void runApp(Widget app) {final WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();assert(binding.debugCheckZone('runApp'));binding..scheduleAttachRootWidget(binding.wrapWithDefaultView(app))..scheduleWarmUpFrame();
}

runApp的代码很简单，传递一个Widget参数，然后执行了三行代码，三行代码代表了Flutter App启动的主要三个流程：

• Binding初始化(ensureInitialized)
• 绑定根节点(scheduleAttachRootWidget)
• 绘制热身帧(scheduleWarmUpFrame)

接下来，我们就按照上面的流程来分析下Flutter App的启动流程。

Binding初始化

WidgetsFlutterBinding的源码比较简单，如下所示。

class WidgetsFlutterBinding extends BindingBase with GestureBinding, SchedulerBinding, ServicesBinding, PaintingBinding, SemanticsBinding, RendererBinding, WidgetsBinding {static Widg