HarmonyOS 如何让自定义类中的属性变化引起UI刷新？

export struct MyComponent {  
  @State vm: MyViewModel = new MyViewModel()  
  
  build() {  
    Column() {  
      Text(this.vm.title)  
      Button('click').onClick(() => {  
        this.vm.setTitle('我的标题2')  
      })  
    }  
  }  
}  
  
  
class MyViewModel {  
  title: string = "我的标题1"  
  
  setTitle(title: string): MyViewModel {  
    this.title = title  
    return this  
  }  
}