CustomWidget的自定義組件的注釋還是比較清晰的
參考文檔Flutter實戰

import 'package:flutter/cupertino.dart';
import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
/*
* 如果組件不會包含子組件，則我們可以直接繼承自 LeafRenderObjectWidget ，它是 RenderObjectWidget
* LeafRenderObjectWidget 適用于 沒有子 Widget 的 RenderObject（例如 Container）。
* */
class CustomWidget extends LeafRenderObjectWidget{//創建RenderObjec,返回 RenderObject@overrideRenderObject createRenderObject(BuildContext context) {// TODO: implement createRenderObjectreturn RenderCustomObject();}//更新RenderObj@overridevoid updateRenderObject(BuildContext context, covariant RenderObject renderObject) {// TODO: implement updateRenderObjectsuper.updateRenderObject(context, renderObject);}@overrideLeafRenderObjectElement createElement() {// TODO: implement createElementreturn super.createElement();}}//RenderBox 是 Flutter 最常見的渲染對象，用于 布局 和 繪制
//畫個紅色的盒子
class RenderCustomObject extends RenderBox{Color color = Colors.red;//實現布局邏輯@overridevoid performLayout() {// TODO: implement performLayoutsize = const Size(100, 100);}//實現繪制,繪制內容
@overridevoid paint(PaintingContext context, Offset offset) {// TODO: implement paintfinal paint = Paint()..color = color;context.canvas.drawRect(offset & size, paint);}//允許點擊事件命中當前控件，攔截響應鏈上的響應@overridebool hitTestSelf(Offset position) {// TODO: implement hitTestSelfreturn true;}//處理點擊事件，監聽點擊事件，改變顏色，并調用 markNeedsPaint() 觸發重繪@overridevoid handleEvent(PointerEvent event, HitTestEntry entry) {if (event is PointerDownEvent) {color = color == Colors.blue ? Colors.green : Colors.blue;markNeedsPaint(); // 重新繪制}}}