HarmonyOS 关于自定义事件回调的方法中，this为undefine

//CustomDialogExample.ets  
@CustomDialog  
export struct CustomDialogExample {  
  cancel?: () => void  
  confirm?: () => void  
  controller: CustomDialogController  
  build() {  
    Column() {  
      Text('我是内容').fontSize(20).margin({ top: 10, bottom: 10 })  
      Flex({ justifyContent: FlexAlign.SpaceAround }) {  
        Button('cancel')  
          .onClick(() => {  
            this.controller.close()  
            if (this.cancel) {  
              this.cancel()  
            }  
          }).backgroundColor(0xffffff).fontColor(Color.Black)  
        Button('confirm')  
          .onClick(() => {  
            this.controller.close()  
            if (this.confirm) {  
              this.confirm()  
            }  
          }).backgroundColor(0xffffff).fontColor(Color.Red)  
      }.margin({ bottom: 10 })  
    }  
  }  
}
//CustomDialogUser.ets  
import { CustomDialogExample } from '../view/CustomDialogExample'  
@Entry  
@Component  
struct CustomDialogUser {  
  dialogController: CustomDialogController = new CustomDialogController({  
    builder: CustomDialogExample({  
      cancel: ()=> { this.onCancel() },  
      confirm: ()=> { this.onAccept() },  
    }),  
  })  
  onCancel() {  
    console.info('Callback when the first button is clicked')  
  }  
  onAccept() {  
    console.info('Callback when the second button is clicked')  
  }  
  build() {  
    Column() {  
      Button('click me')  
        .onClick(() => {  
          this.dialogController.open()  
        })  
    }.width('100%').margin({ top: 5 })  
  }  
}