HarmonyOS 鸿蒙Next 在子组件写了一个方法，在父组件想直接调用这个方法，该如何实现呢？

参考：

[@Component](/user/Component)
struct Child {
 [@State](/user/State) private text: string = '初始值'
 private controller: ChildController = new ChildController();

 aboutToAppear() {
   if (this.controller) {
     this.controller.changeText = this.changeText
   }
   console.log('aaa')
 }

 private changeText = (value: string) => {
   this.text = value
   console.log('bbb')
 }

 build() {
   Column() {
     Text(this.text)
   }
 }
}

class ChildController {
 changeText = (value: string) => {
   console.log('11111')
 }
}

export let ChildRef = new ChildController()

[@Entry](/user/Entry)
[@Component](/user/Component)
struct Parent {
 // ChildRef = new ChildController()
 [@State](/user/State) noShow: boolean = false

 build() {
   Column() {
     Text('获取Child的exposeMethods!').fontSize('18vp').fontColor(Color.Gray)
     Divider()
     Child({ controller: ChildRef })
     Child()
     Button('Parent调用childer的changeText').onClick(() => {
       ChildRef.changeText('Parent调用childer的changeText')
     })
   }
 }
}