为了对嵌套类对象属性变化直接观测，华为提供了ObservedV2和Trace装饰器。这两个装饰器必须搭配使用，单独使用任何一个都不会起任何作用；在继承类中也可监测；ObservedV2的类实例目前不支持使用JSON.stringify进行序列化，需通过new操作符实例化后，才具备被观测变化的能力。与V1版本相比（使用@ObjectLink装饰器与自定义组件来实现观测），使用起来更加方便。

嵌套类场景

在下面场景中老师(Teacher)尹山木，有个学生(Student)丁云飞，高一有三门课程(语文，数学，英语)，升到高二增加了一门化学课。

export class Teacher{name:string = "尹山木"student:Studentconstructor(stu:Student) {this.student = stu}
}
export class Student{name:string = "丁云飞"course:Courseconstructor(c:Course) {this.course = c}
}
@ObservedV2
export class Course{@Trace courses:Array<string> = []constructor() {this.courses = ["语文","数学","英语"]}
}
@Entry
@ComponentV2
struct Index {
@Local teacher:Teacher = new Teacher(new Student(new Course()))build() {Column({space:20}){Text("老师:" + this.teacher.name).fontSize(20)Text("学生:" + this.teacher.student.name).fontSize(18)Row({space:6}){ForEach(this.teacher.student.course.courses,(course:string,index)=>{Text("课程:" + course).fontSize(16)})}.width('100%').justifyContent(FlexAlign.Start).alignItems(VerticalAlign.Center)Button("升上二年级").onClick(()=>{this.teacher.student.course.courses.push("化学")})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

运行效果点击升上二年级，可以看到课程增加了一门化学。

继承类场景

祖孙三人，每过一年，年龄增加一岁。

@ObservedV2
export class GrandFather{@Trace age:number = 0constructor(age:number) {this.age = age;}
}
export class Father extends GrandFather{constructor(age:number) {super(age)}
}
export class Son extends Father{constructor(age: number) {super(age)}
}
@Entry
@ComponentV2
struct Index {
@Local son:Son = new Son(2)build() {Column({space:20}){Text("孩子今年：" + this.son.age + "岁了！").fontSize(20)Button("过了一年").onClick(()=>{this.son.age++})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

点击过了一年孩子会增长一岁。

Trace装饰基础类型的数组

ObservedV2监听模型numArrModel的numberArr数组的增加，同时刷新UI

@ObservedV2
export class numArrModel{id:number = 0@Trace numberArr:Array<number> = [0,10,5]
}
@Entry
@ComponentV2
struct Index {
@Local numModel:numArrModel = new numArrModel()build() {Column({space:20}){ForEach(this.numModel.numberArr,(item:number,index)=>{Text(''+item).fontSize(20)})Button('增加一个数字').onClick(()=>{this.numModel.numberArr.push(11)})Button('减少一个数字').onClick(()=>{this.numModel.numberArr.pop()})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

Trace装饰对象数组

Trace装饰对象数组studends，以及student的属性age。当数组长度和age改变时页面会刷新。

@ObservedV2
export class Student{@Trace age:number = 1
}
@ObservedV2
export class Classes{id:number = 3@Trace studends:Student[] = []constructor(stus:Student[]) {this.studends = stus}
}
@Entry
@ComponentV2
struct Index {
@Local classModel:Classes = new Classes([new Student(),new Student(),new Student()])build() {Column({space:20}){Column(){Text("班级:"+this.classModel.id).fontSize(20)Text("学生数量:"+this.classModel.studends.length+"人").fontSize(20)}Column(){ForEach(this.classModel.studends,(stu:Student,index)=>{Text("年龄:"+stu.age).fontSize(20)})}Button('增加一个学生').onClick(()=>{this.classModel.studends.push(new Student())})Button('第一名学生年龄增加一岁').onClick(()=>{if (this.classModel.studends.length > 0) {this.classModel.studends[0].age++}})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

Trace装饰Map类型

Trace装饰的Map类型属性，当发生set、clear、delete事件时会被监测到。

@ObservedV2
export class textMapModel{@Trace textMap:Map<number,string> = new Map([[0,'a'],[1,'b'],[2,'c']])
}
@Entry
@ComponentV2
struct Index {
@Local mapInfo:textMapModel = new textMapModel()build() {Column({space:20}){ForEach(Array.from(this.mapInfo.textMap.entries()), (item: [number, string]) => {Text(`${item[0]}`).fontSize(30)Text(`${item[1]}`).fontSize(30)Divider()})Button('初始化').onClick(()=>{this.mapInfo.textMap = new Map([[0,'z'],[1,'x'],[2,'c']])})Button('增加一个').onClick(()=>{this.mapInfo.textMap.set(3,'v')})Button('删除一个').onClick(()=>{this.mapInfo.textMap.delete(0)})Button('清除').onClick(()=>{this.mapInfo.textMap.clear()})Button('改变值').onClick(()=>{this.mapInfo.textMap.set(0,'city')})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

Trace装饰Set类型

Trace装饰的Set类型属性可以观测到add, clear, delete等

@ObservedV2
export class Info{@Trace memberSet:Set<number> = new Set([0,1,2,3,4,5,6,])
}
@Entry
@ComponentV2
struct Index {
@Local memberInfoModel:Info = new Info()build() {Column({space:20}){Row(){ForEach(Array.from(this.memberInfoModel.memberSet.values()),(item:number)=>{Text(``+item).fontSize(20).margin({left:6})})}Button('add').onClick(()=>{this.memberInfoModel.memberSet.add(10)})Button('clear').onClick(()=>{this.memberInfoModel.memberSet.clear()})Button('delete').onClick(()=>{this.memberInfoModel.memberSet.delete(0)})}.justifyContent(FlexAlign.Start).alignItems(HorizontalAlign.Start).padding({left:20})}
}

Trace装饰Date类型

@Trace装饰的Date类型属性可以观测调用API带来的变化，包括 setFullYear、setMonth、setDate、setHours、setMinutes、setSeconds、setMilliseconds、setTime、setUTCFullYear、setUTCMonth、setUTCDate、setUTCHours、setUTCMinutes、setUTCSeconds、setUTCMilliseconds。因为Info类被@ObservedV2装饰且属性selectedDate被@Trace装饰，点击Button('set selectedDate to 2023-07-08')对selectedDate赋值也可以观测到变化。