Flutter开发进阶之瞧瞧State

本文主要是介绍Flutter开发进阶之瞧瞧State，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

Flutter开发进阶之瞧瞧State

书接上回
上回说到StatefulWidget会将自身作为参数创建StatefulElement，然后StatefulElement的创建过程首先要调用_state = widget.createState()，会创建并持有一个state通过对其生命周期的管理去对Widget进行刷新，创建state后还会将自身交给state持有state._element = this;。
接下来会通过解析State的构成去理解State。
Flutter开发进阶
首先瞧瞧State里有些什么？

@optionalTypeArgs
abstract class State<T extends StatefulWidget> with Diagnosticable {T get widget => _widget!;T? _widget;_StateLifecycle _debugLifecycleState = _StateLifecycle.created;bool _debugTypesAreRight(Widget widget) => widget is T;BuildContext get context {assert(() {if (_element == null) {throw FlutterError('This widget has been unmounted, so the State no longer has a context (and should be considered defunct). \n''Consider canceling any active work during "dispose" or using the "mounted" getter to determine if the State is still active.',);}return true;}());return _element!;}StatefulElement? _element;bool get mounted => _element != null;@protected@mustCallSupervoid initState() {assert(_debugLifecycleState == _StateLifecycle.created);if (kFlutterMemoryAllocationsEnabled) {MemoryAllocations.instance.dispatchObjectCreated(library: _flutterWidgetsLibrary,className: '$State',object: this,);}}@mustCallSuper@protectedvoid didUpdateWidget(covariant T oldWidget) { }@protected@mustCallSupervoid reassemble() { }@protectedvoid setState(VoidCallback fn) {assert(() {if (_debugLifecycleState == _StateLi