Flutter App launch

All the code refence from flutter version 3.29.3, dart 3.7.2.

RunApp

[runApp] which bootstraps a widget tree and renders it into a default [FlutterView]

void runApp(Widget app) {
  final WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
  _runWidget(binding.wrapWithDefaultView(app), binding, 'runApp');
}

WidgetsFlutterBinding.ensureInitialized

The method initInstances will be called in class WidgetsFlutterBinding 's constructor. which will set the WidgetsBinding's instance.

_runWidget

Method _runWidget will build the element tree.

void _runWidget(Widget app, WidgetsBinding binding, String debugEntryPoint) {
  binding
    ..scheduleAttachRootWidget(app)
    ..scheduleWarmUpFrame();
}

WidgetsFlutterBinding.wrapWithDefaultView

Generate the View widget which contain a FlutterView will be drawn. The View also includes

Widget wrapWithDefaultView(Widget rootWidget) {
    return View(
      view: platformDispatcher.implicitView!,
      deprecatedDoNotUseWillBeRemovedWithoutNoticePipelineOwner: pipelineOwner,
      deprecatedDoNotUseWillBeRemovedWithoutNoticeRenderView: renderView,
      child: rootWidget,
    );
  }

The View 's purpose is building the render tree.

Build child element tree

After attach to root widget, the build owner will start to mount child which will build a element tree.

This is the flow of mount belong to RootElement.

The render tree will aslo be built when element changed.

After that, it will ask to refresh to screen.