runApp function

Implementation

// TODO(goderbauer): Update the paragraph below to include the Window widget once that exists.
/// The [runApp] method renders the provided `app` widget into the
/// [PlatformDispatcher.implicitView] by wrapping it in a [View] widget, which
/// will bootstrap the render tree for the app. Apps that want to control which
/// [FlutterView] they render into can use [runWidget] instead.
///
/// The widget is given constraints during layout that force it to fill the
/// entire view. If you wish to align your widget to one side of the view
/// (e.g., the top), consider using the [Align] widget. If you wish to center
/// your widget, you can also use the [Center] widget.
///
/// Calling [runApp] again will detach the previous root widget from the view
/// and attach the given widget in its place. The new widget tree is compared
/// against the previous widget tree and any differences are applied to the
/// underlying render tree, similar to what happens when a [StatefulWidget]
/// rebuilds after calling [State.setState].
///
/// Initializes the binding using [WidgetsFlutterBinding] if necessary.
///
/// {@template flutter.widgets.runApp.shutdown}
/// ## Application shutdown
///
/// This widget tree is not torn down when the application shuts down, because
/// there is no way to predict when that will happen. For example, a user could
/// physically remove power from their device, or the application could crash
/// unexpectedly, or the malware on the device could forcibly terminate the
/// process.
///
/// Applications are responsible for ensuring that they are well-behaved
/// even in the face of a rapid unscheduled termination.
///
/// To listen for platform shutdown messages (and other lifecycle changes),
/// consider the [AppLifecycleListener] API.
/// {@endtemplate}
///
/// To artificially cause the entire widget tree to be disposed, consider
/// calling [runApp] with a widget such as [SizedBox.shrink].
///
/// {@template flutter.widgets.runApp.dismissal}
/// ## Dismissing Flutter UI via platform native methods
///
/// An application may have both Flutter and non-Flutter UI in it. If the
/// application calls non-Flutter methods to remove Flutter based UI such as
/// platform native API to manipulate the platform native navigation stack,
/// the framework does not know if the developer intends to eagerly free
/// resources or not. The widget tree remains mounted and ready to render
/// as soon as it is displayed again.
/// {@endtemplate}
///
/// To release resources more eagerly, establish a [platform channel](https://flutter.dev/to/platform-channels)
/// and use it to call [runApp] with a widget such as [SizedBox.shrink] when
/// the framework should dispose of the active widget tree.
///
/// See also:
///
///  * [runWidget], which bootstraps a widget tree without assuming the
///    [FlutterView] into which it will be rendered.
///  * [WidgetsBinding.attachRootWidget], which creates the root widget for the
///    widget hierarchy.
///  * [RenderObjectToWidgetAdapter.attachToRenderTree], which creates the root
///    element for the element hierarchy.
///  * [WidgetsBinding.handleBeginFrame], which pumps the widget pipeline to
///    ensure the widget, element, and render trees are all built.
void runApp(Widget app) {
  final WidgetsBinding binding = WidgetsFlutterBinding.ensureInitialized();
  _runWidget(binding.wrapWithDefaultView(app), binding, 'runApp');
}