组件可见区域变化事件

// xxx.ets
@Entry
@Component
struct ScrollExample {
  scroller: Scroller = new Scroller()
  private arr: number[] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
  @State testTextStr: string = 'test'
  @State testRowStr: string = 'test'

  build() {
    Column() {
      Column() {
        Text(this.testTextStr)
          .fontSize(20)

        Text(this.testRowStr)
          .fontSize(20)
      }
      .height(100)
      .backgroundColor(Color.Gray)
      .opacity(0.3)

      Scroll(this.scroller) {
        Column() {
          Text("Test Text Visible Change")
            .fontSize(20)
            .height(200)
            .margin({ top: 50, bottom: 20 })
            .backgroundColor(Color.Green)
              // 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) => {
              console.info('Test Text isVisible: ' + isVisible + ', currentRatio:' + currentRatio)
              if (isVisible && currentRatio >= 1.0) {
                console.info('Test Text is fully visible. currentRatio:' + currentRatio)
                this.testTextStr = 'Test Text is fully visible'
              }

              if (!isVisible && currentRatio <= 0.0) {
                console.info('Test Text is completely invisible.')
                this.testTextStr = 'Test Text is completely invisible'
              }
            })

          Row() {
            Text('Test Row Visible  Change')
              .fontSize(20)
              .margin({ bottom: 20 })

          }
          .height(200)
          .backgroundColor(Color.Yellow)
          .onVisibleAreaChange([0.0, 1.0], (isVisible: boolean, currentRatio: number) => {
            console.info('Test Row isVisible:' + isVisible + ', currentRatio:' + currentRatio)
            if (isVisible && currentRatio >= 1.0) {
              console.info('Test Row is fully visible.')
              this.testRowStr = 'Test Row is fully visible'
            }

            if (!isVisible && currentRatio <= 0.0) {
              console.info('Test Row is completely invisible.')
              this.testRowStr = 'Test Row is completely invisible'
            }
          })

          ForEach(this.arr, (item:number) => {
            Text(item.toString())
              .width('90%')
              .height(150)
              .backgroundColor(0xFFFFFF)
              .borderRadius(15)
              .fontSize(16)
              .textAlign(TextAlign.Center)
              .margin({ top: 10 })
          }, (item:number) => (item.toString()))

        }.width('100%')
      }
      .backgroundColor(0x317aff)
      .scrollable(ScrollDirection.Vertical)
      .scrollBar(BarState.On)
      .scrollBarColor(Color.Gray)
      .scrollBarWidth(10)
      .onScroll((xOffset: number, yOffset: number) => {
        console.info(xOffset + ' ' + yOffset)
      })
      .onScrollEdge((side: Edge) => {
        console.info('To the edge')
      })
      .onScrollStop(() => {
        console.info('Scroll Stop')
      })

    }.width('100%').height('100%').backgroundColor(0xDCDCDC)
  }
}