class DemoWidget extends StatefulWidget {
  const DemoWidget({super.key});
  @override
  State<DemoWidget> createState() => _DemoWidgetState();
}
class _DemoWidgetState extends State<DemoWidget> {
  @override
  Widget build(BuildContext context) {
    return Container();
  }
}

首先

會(huì)執(zhí)行StatefulWidget 中相關(guān)的方法

* 1 執(zhí)行StatefulWidget的構(gòu)造函數(shù)（Constructor）來(lái)創(chuàng)建StatefuleWidget

* 2 執(zhí)行StateWidget的createState 方法，來(lái)創(chuàng)建一個(gè)維護(hù)StatefulWidget 的State對(duì)象

其次

調(diào)用createState 創(chuàng)建State對(duì)象時(shí)候，執(zhí)行State類(lèi)相關(guān)的方法

* 1 執(zhí)行State 類(lèi)的構(gòu)造方法（Constructor）來(lái)創(chuàng)建State 對(duì)象

* 2 執(zhí)行initState,我們通常會(huì)在這個(gè)方法中執(zhí)行一些數(shù)據(jù)初始化的操作或者也可能發(fā)送數(shù)據(jù)請(qǐng)求

   @override
  void initState() {
    super.initState();
    
  }

* 3 執(zhí)行didChangeDependencies 方法，這個(gè)方法會(huì)在兩種情況下調(diào)用

調(diào)用initState 會(huì)調(diào)用
從其他對(duì)象依賴一些數(shù)據(jù)發(fā)生改變的時(shí)候，會(huì)調(diào)用

* 4 執(zhí)行build 方法，來(lái)看一下當(dāng)前的widget 需要渲染哪些Widget,構(gòu)建對(duì)應(yīng)的widgets

* 5 當(dāng)前的widget 不再使用的時(shí)候，會(huì)調(diào)用dispose 進(jìn)行銷(xiāo)毀

* 6 手動(dòng)調(diào)用setState方法，會(huì)根據(jù)最新的狀態(tài)（數(shù)據(jù)）開(kāi)重新調(diào)用build 方法，構(gòu)建對(duì)應(yīng)的Widgets

* 7 執(zhí)行didUpdateWidget 方法是當(dāng)父Widget 觸發(fā)重建（rebuild）時(shí)，系統(tǒng)會(huì)調(diào)用didUpdateWidget方法

二 SetState

 /// Marks the element as dirty and adds it to the global list of widgets to
  /// rebuild in the next frame.
  ///
  /// Since it is inefficient to build an element twice in one frame,
  /// applications and widgets should be structured so as to only mark
  /// widgets dirty during event handlers before the frame begins, not during
  /// the build itself.
  void markNeedsBuild() {
void scheduleBuildFor(Element element) 
    if (_dirty) {
      owner!.scheduleBuildFor(this);
    }
    if (hadDependencies) {
      didChangeDependencies();
    }
 }
 /// Adds an element to the dirty elements list so that it will be rebuilt
  /// when [WidgetsBinding.drawFrame] calls [buildScope].
  void scheduleBuildFor(Element element) {
}

setState的調(diào)用其實(shí)是element 會(huì)調(diào)用 markNeedsBuild 這個(gè)方法，標(biāo)記當(dāng)前的element 需要更新。dirty 設(shè)置為true.

方法的最后會(huì)調(diào)用一個(gè)BuildOwner類(lèi)中的

scheduleBuildFor 方法，這個(gè)方法注釋寫(xiě)的很清楚，就是吧這個(gè)element 添加到dirty elements list 中去，當(dāng)WidgetsBinding.drawFrame 去走更新的流程