HarmonyOS 鸿蒙Next 异步获取数据，列表无法更新视图

@Entry
@Component
struct MainPage {
  @State WaterfallObj: Record<string, Item[]> = {};
  @State waterFlowData: WaterFlowDataSource = new WaterFlowDataSource()
  aboutToAppear(): void {
    setTimeout(() => {
      this.WaterfallObj['recommend'] = [{ label: '1' }, { label: '2' }, { label: '3' }, { label: '4' }];
      this.WaterfallObj['recommend'].forEach((item: Item)=>{
        this.waterFlowData.pushData(item)
      })
    }, 2000)
  }
  build() {
    Row() {
      Column() {
        Waterfall({ waterFlowData: this.waterFlowData })
      }
      .width('100%')
    }
    .height('100%')
  }
}
@Component
struct Waterfall {
  @ObjectLink waterFlowData: WaterFlowDataSource;
  build() {
    WaterFlow() {
      LazyForEach(this.waterFlowData, (item: Item) => {
        FlowItem() {
          Column() {
            Text(item.label)
              .height(50)
          }
        }
        .width('100%')
      }, (item: Item) => JSON.stringify(item))
    }
    .columnsTemplate("1fr 1fr")
    .columnsGap(10)
    .rowsGap(5)
    .width('100%')
    .height('100%')
  }
}
@Observed
class Item {
  label: string = '';
}
/**
 * 实现IDataSource接口的对象，用于瀑布流组件加载数据
 */
@Observed
export class WaterFlowDataSource implements IDataSource {
  private dataArray: Item[] = []
  private listeners: DataChangeListener[] = []
  constructor(data: Item[] = []) {
    this.dataArray = data
  }
  // 获取索引对应的数据
  public getData(index: number): Item {
    return this.dataArray[index]
  }
  // 获取数据总数
  public totalCount(): number {
    return this.dataArray.length
  }
  // 注册改变数据的控制器
  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      this.listeners.push(listener)
    }
  }
  public pushData(data: Item): void {
    this.dataArray.push(data);
    this.notifyDataAdd(this.dataArray.length - 1);
  }
  // 注销改变数据的控制器
  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener)
    if (pos >= 0) {
      this.listeners.splice(pos, 1)
    }
  }
  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index);
    })
  }
}