如何在父组件中调用子组件封装的方法

@Component 
struct Child  { 
  @State private text: string = '初始值' 
  private controller: ChildController = new ChildController(); 
  
  aboutToAppear() { 
    if(this.controller) { 
//给controller对应的方法赋值 
      this.controller.changeText = this.changeText 
    } 
  } 
//封装的能力 
  private changeText = (value: string) =>{ 
    this.text = value 
  } 
  
  build() { 
    Column() { 
      Text(this.text) 
    } 
  } 
} 
  
//定义controller对象 
class ChildController { 
  changeText = (value: string) => {} 
} 
  
@Entry 
@Component 
struct Parent { 
  private  ChildRef = new ChildController() 
  build() { 
    Column() { 
      Text('调用Child的changeText').fontSize('18vp').fontColor(Color.Gray) 
      Divider() 
      Child({ controller:this. ChildRef }) 
      Button('Parent调用childer的changeText').onClick(() => { 
        this.ChildRef.changeText('Parent调用childer的changeText') 
      }) 
    } 
    .justifyContent(FlexAlign.Center) 
    .width("100%") 
    .height("100%") 
  } 
}