元素生命周期 
元素从创建、添加、挂载,到移除、解除挂载、销毁的全过程,可在初始化事件中监听。
示例 
生命周期中的不同状态会通过 ChildEvent、 PropertyEvent 进行通知。
监听元素生命周期事件 
初始化方式监听
ts
// #监听元素生命周期事件 [通过 event 对象监听] import { Leafer, Rect } from 'leafer-ui'  const leafer = new Leafer({ view: window })  const rect = new Rect({  x: 100,  y: 100,  width: 200,  height: 200,  fill: '#32cd79',  cornerRadius: [50, 80, 0, 80],  draggable: true,  event: {  created() {  console.log('rect created')  },  mounted: () => {  console.log('mounted, leafer', rect.leafer) // 元素已挂载到 leafer 的树结构上,可以被渲染  },  unmounted() {  console.log('unmounted')  },  } })  leafer.add(rect)通过 on 监听
ts
// #监听元素生命周期事件 [通过 on 监听] import { Leafer, Rect } from 'leafer-ui'  const leafer = new Leafer({ view: window })  const rect = new Rect({  x: 100,  y: 100,  width: 200,  height: 200,  fill: '#32cd79',  cornerRadius: [50, 80, 0, 80],  draggable: true })  leafer.add(rect)  rect.on('created', () => {  console.log('rect created') })   rect.on('mounted', () => {  console.log('mounted, leafer', rect.leafer) // 元素已挂载到 leafer 的树结构上,可以被渲染 })   rect.on('unmounted', () => {  console.log('unmounted') })