HarmonyOS 鸿蒙Next Observed 以及@ObjectLink无法更新UI

@Observed
class DateClass extends Date {
  constructor(args: number | string) {
    super(args)
  }
}

@Observed
class ClassB {
  public a: DateClass;

  constructor(a: DateClass) {
    this.a = a;
  }
}

@Component
struct ViewA {
  label: string = ‘date’;
  @ObjectLink classB: ClassB;

  build() {
    Column() {
      Button(child increase the day by 1)
        .onClick(() => {
          this.classB.a.setDate(this.classB.a.getDate() + 1);
          console.log(‘date:’+this.classB.a);
        })
      DatePicker({
        start: new Date(‘1970-1-1’),
        end: new Date(‘2100-1-1’),
        selected: this.classB.a
      })
    }
  }
}

@Entry
@Component
struct ViewB {
  @State b: ClassB = new ClassB(new DateClass(‘2023-1-1’));

  build() {
    Column() {
      ViewA({ label: ‘date’, classB: this.b })

      Button(parent update the new date)
        .onClick(() => {
          this.b.a = new DateClass(‘2023-07-07’);
        })
      Button(ViewB: this.b = new ClassB(new DateClass('2023-08-20')))
        .onClick(() => {
          this.b = new ClassB(new DateClass(‘2023-08-20’));
        })
    }
  }
}

Button(child increase the day by 1)这个按钮日期加1，DatePicker({ start: new Date(‘1970-1-1’), end: new Date(‘2100-1-1’), selected: this.classB.a }) UI为什么监测不到？UI没更新，求大神讲解原因