HarmonyOS list组件，如何检测子item处于屏幕窗口内，进行曝光埋点

可以使用组件可见区域变化事件onVisibleAreaChange，组件可见区域变化时触发该回调https://developer.huawei.com/consumer/cn/doc/harmonyos-references-V5/ts-universal-component-visible-area-change-event-V5

示例demo 如下：

// xxx.ets
@Entry
@Component
struct ListExample {
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

  build() {
    Column() {
      List({ space: 20, initialIndex: 0 }) {
        ForEach(this.arr, (item: number) => {
          ListItem() {
            Text('' + item)
              .width('100%').height(100).fontSize(16)
              .textAlign(TextAlign.Center).borderRadius(10).backgroundColor(0xFFFFFF)
          }
          // 通过设置ratios为[0.0, 1.0]，实现当组件完全显示或完全消失在屏幕中时触发回调
          .onVisibleAreaChange([0.0, 1.0], (isVisible: boolean, currentRatio: number) => {
            if (isVisible && currentRatio >= 1.0) {
              console.info('cbl Test Text is fully visible. currentRatio:' + currentRatio +'可见 item'+item)
            }
            if (!isVisible && currentRatio <= 0.0) {
              console.info('cbl Test Text is completely invisible.'+'不可见 item'+item)
            }
          })
        }, (item: string) => item)
      }
      .listDirection(Axis.Vertical) // 排列方向
      .scrollBar(BarState.Off)
      .friction(0.6)
      .divider({ strokeWidth: 2, color: 0xFFFFFF, startMargin: 20, endMargin: 20 }) // 每行之间的分界线
      .edgeEffect(EdgeEffect.Spring) // 边缘效果设置为Spring
      .onScrollIndex((firstIndex: number, lastIndex: number, centerIndex: number) => {
        console.info('first' + firstIndex)
        console.info('last' + lastIndex)
        console.info('center' + centerIndex)
      })
      .onScroll((scrollOffset: number, scrollState: ScrollState) => {
        console.info(`onScroll scrollState = ScrollState` + scrollState + `, scrollOffset = ` + scrollOffset)
      })
      .width('90%')
    }
    .width('100%')
    .height('100%')
    .backgroundColor(0xDCDCDC)
    .padding({ top: 5 })
  }
}