HarmonyOS 组件外定义的class如何合内部UI做双向绑定，以及interface的用法？

@Entry 
@Component 
struct TextExample1 { 
  @State nvsTimeline: NvsTimeline = new NvsTimeline("a") 
  private mCallBack: callback = new callback(); 
  build() { 
    Flex({ direction: FlexDirection.Column, alignItems: ItemAlign.Start, justifyContent: FlexAlign.SpaceBetween }) { 
      TextInput({ text: $$this.nvsTimeline.name }) 
 
      Button("xxx").onClick(() => { 
        let a: NvsTimeline = this.nvsTimeline 
        this.mCallBack.onPlaybackPreloadingCompletion(a) 
      }) 
 
    }.height(600).width(350).padding({ left: 35, right: 35, top: 35 }) 
  } 
} 
class callback implements PlaybackCallback { 
  onPlaybackPreloadingCompletion(timeline: NvsTimeline): void { 
    console.log("xxxxxxxxxxxxxxxxxx", timeline.name) 
    timeline.name = "bbbbb" 
  } 
} 
export interface PlaybackCallback { 
  onPlaybackPreloadingCompletion(timeline: NvsTimeline): void 
} 
@Observed 
class NvsTimeline { 
  name: string; 
  constructor(name: string) { 
    this.name = name 
  } 
}