HarmonyOS 鸿蒙Next list加载上一页如何实现

// Basic implementation of IDataSource to handle data listener
abstract class BasicDataSource<T> implements IDataSource {
  private listeners: DataChangeListener[] = []
  abstract totalCount(): number
  abstract getData(index: number): T
  registerDataChangeListener(listener: DataChangeListener): void {
    if (this.listeners.indexOf(listener) < 0) {
      console.info('add listener')
      this.listeners.push(listener)
    }
  }
  unregisterDataChangeListener(listener: DataChangeListener): void {
    const pos = this.listeners.indexOf(listener);
    if (pos >= 0) {
      console.info('remove listener')
      this.listeners.splice(pos, 1)
    }
  }
  notifyDataReload(): void {
    this.listeners.forEach(listener => {
      listener.onDataReloaded()
    })
  }
  notifyDataAdd(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataAdd(index)
    })
  }
  notifyDataChange(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataChange(index)
    })
  }
  notifyDataDelete(index: number): void {
    this.listeners.forEach(listener => {
      listener.onDataDelete(index)
    })
  }
  notifyDataMove(from: number, to: number): void {
    this.listeners.forEach(listener => {
      listener.onDataMove(from, to)
    })
  }
}
export class MyDataSource<T> extends BasicDataSource<T> {
  private dataArray: T[] = []
  public totalCount(): number {
    return this.dataArray.length
  }
  public getData(index: number): T {
    console.log("zxy List cacheCountTest3 getData = " + index)
    return this.dataArray[index]
  }
  public addData(index: number, data: T): void {
    this.dataArray.splice(index, 0, data) // 在index位置增加data
    this.notifyDataAdd(index)
  }
  public dataReload(): void {
    this.notifyDataReload()
  }
  public pushData(data: T): void {
    this.dataArray.push(data)
    this.notifyDataAdd(this.dataArray.length - 1)
  }
  public deleteIndex(index: number): void {
    this.dataArray.splice(index, 1) // 在index位置删除1个数据
    this.notifyDataDelete(index)
  }
  public deleteData(data: T): void {
    let index = this.dataArray.indexOf(data)
    this.dataArray.splice(index, 1) // 在index位置删除1个数据
    this.notifyDataDelete(index)
  }
  public moveData(from: number, to: number) {
    // [this.dataArray[from], this.dataArray[to]] = [this.dataArray[to], this.dataArray[from]]
    this.notifyDataMove(from, to)
  }
  public changeData(index: number, data: T) {
    this.dataArray[index] = data
    this.notifyDataChange(index)
  }
  public indexOf(data: T): number {
    return this.dataArray.indexOf(data)
  }
}
@Entry
@Component
struct page240524163225079 {
  startIndex: number = 10
  loading: boolean = false;
  // [@State](/user/State) arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
  private arr: MyDataSource<number> = new MyDataSource()
  private scroller: Scroller = new Scroller()
  @State num: number = 60
  aboutToAppear(): void {
    for (let i = 0; i < 11; i++) {
      this.arr.pushData(i)
    }
  }
  build() {
    Column() {
      Button('点击开始定时器看看下来加载是否刷新')
        .onClick(() => {
          setInterval(() => {
            this.num--
          }, 1000)
        })
      List({ initialIndex: 10, space: 20, scroller: this.scroller }) {
        LazyForEach(this.arr, (item: number) => {
          ListItem() {
            Column() {
              Text('' + item + "----------" + this.num)
                .width('100%')
                .height(100)
                .fontSize(16)
                .textAlign(TextAlign.Center)
                .borderRadius(10)
                .backgroundColor(0xFFFFFF)
              Image($r('app.media.background'))
                .height(200)
                .height(200)
            }
          }
        }, (item: string) => item)
      }.width('90%')
      .scrollBar(BarState.Off)
      .onScrollIndex((start: number) => {
        this.startIndex = start;
        console.log('this.startIndex', this.startIndex)
        if (start < 5 && !this.loading) {
          setTimeout(() => {
            let indexOffset = this.scroller.getItemRect(this.startIndex).y;
            let a = this.arr.getData(0)
            for (let i = 0; i < 10; i++) {
              this.arr.addData(0, a - i - 1);
            }
            this.scroller.scrollToIndex(this.startIndex + 10);
            this.scroller.scrollBy(0, -indexOffset);
            this.loading = false;
          }, 1000)
          this.loading = true;
        }
      })
    }.width('100%').height('100%').backgroundColor(0xDCDCDC).padding({ top: 5 })
  }
}