getUniqueId是API 12提供的接口，用来获取当前Component的UniqueId。UniqueId为系统为每个组件分配的Id，可保证当前应用中的唯一性。
测试代码如下，分别在PageOne、PageTwo、PageThree三个Component的aboutToAppear打印各自的UniqueId:

  aboutToAppear(): void {
    this.test();
  }
  test(){
    let uniqueId: number = this.getUniqueId();
    console.info('pageTwo uniqueId == ' + uniqueId);
  }

完整代码如下：

@Entry
@Component
struct PageOne {
  build() {
    Row() {
      Column({ space: 10 }) {
        PageTwo()
        PageThree()
      }
      .width('100%')
    }
    .height('100%')
    .backgroundColor(0xF1F3F5)
  }
  aboutToAppear(): void {
    this.test();
  }
  test(){
    let uniqueId: number = this.getUniqueId();
    console.info('pageOne uniqueId == ' + uniqueId);
  }
}
@Component
export struct PageTwo {
  @State message: string = 'Hello World 2';
  build() {
      Text(this.message)
        .id('PageTwo HelloWorld ')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)

  }
  aboutToAppear(): void {
    this.test();
  }
  test(){
    let uniqueId: number = this.getUniqueId();
    console.info('pageTwo uniqueId == ' + uniqueId);
  }
}

@Component
export struct PageThree {
  @State message: string = 'Hello  World 3';

  build() {
      Text(this.message)
        .id('PageTwo HelloWorld ')
        .fontSize(50)
        .fontWeight(FontWeight.Bold)

  }
  aboutToAppear(): void {
    this.test();
  }
  test(){
    let uniqueId: number = this.getUniqueId();
    console.info('pageThree uniqueId == ' + uniqueId);
  }
}

运行后，日志输出如下所示：

10-24 10:14:56.135   46525-46525  A03D00/com.exa...simplme/JSAPP pid-46525             I     pageOne uniqueId == 3
10-24 10:14:56.136   46525-46525  A03D00/com.exa...simplme/JSAPP pid-46525             I     pageTwo uniqueId == 7
10-24 10:14:56.136   46525-46525  A03D00/com.exa...simplme/JSAPP pid-46525             I     pageThree uniqueId == 8