let c = 0;

class DS implements IDataSource {
  private arr: any[] = [];
  private dcl: DataChangeListener;

  constructor() {
    this.arr = Array(100).fill(0).map((v,i) => `${i}`);
    //console.log('pikalov DS.constructor');
  }

  totalCount(): number {
    //console.log('pikalov', 'totalCount');
    return this.arr.length;
  }

  getData(index: number): any {
    //console.log('pikalov', `getData(${index})`)
    return this.arr[index];
  }

  registerDataChangeListener(listener: DataChangeListener): void {
    //console.log('pikalov', 'registerDataChangeListener')
    this.dcl = listener;
  }

  unregisterDataChangeListener(listener: DataChangeListener): void {
    //console.log('pikalov', 'un-registerDataChangeListener')
  }
}

@Entry
@Component
struct MyComponent {
  @State ds:DS = new DS();

  scroller: Scroller = new Scroller();

  build() {
    Column() {
      Text('1_lazy.ets')

      Row() {
        Button('Scroll top').onClick(() => this.scroller.scrollToIndex( 0))
        Button('Scroll mid').onClick(() => this.scroller.scrollToIndex(50))
      }

      List({ space: 3, scroller:this.scroller }) {
        LazyForEach(this.ds, (item) => {
          ListItem() {
            Text(`item: ${item} ${c%2}`).fontSize(32 + 32 * (c%2) )//(128)
          }
          .onAppear(()=>{
            //console.error("@Component LazyForEach > ListItem onAppear")
          })
        }, 
          (item) => item
        )//.cachedCount(5)
      }

    }
  }
}