arkUI自定义组件，父组件如何获取子组件对象，调用其方法

@Entry
@Component
struct Index {
  @State message: string = 'Hello World'
  customComponent: CustomComponent = CustomComponent()
  build() {
    Row() {
      Column() {
        Text(this.message)
          .fontSize(50)
          .fontWeight(FontWeight.Bold)
          .onClick(() => {
            this.d.caretPosition(3)
            hilog.isLoggable(0x0000, 'testTag', hilog.LogLevel.INFO);
            hilog.info(0x0000, 'testTag', 'Test NAPI 2 + 3 = %{public}d', testNapi.add(2, 3));
          })
          this.customComponent
      }
      .width('100%')
    }
    .height('100%')
  }
}