HarmonyOS json转换成对象

json转自定义class对象时，需要将class对象new出来，这样才是真正转成了class对应的model。如果数据结构比较复杂，数据量比较大，不想在解析的时候，每个对象都new一次，建议使用第三库reflect-metadata 和 class-transformer，安装方法：

ohpm install class-transformer 
ohpm install reflect-metadata

参考代码：

import 'reflect-metadata';
import { plainToClass, Type } from 'class-transformer';

class ResponseObj {
  @Type(() => Person)
  data: Person[] = [];
}

@Entry
@Component
struct TestJson {
  @State list: Person[] = [];
  @State message: string = 'Click me';
  aboutToAppear(): void {
    let str = '{"data" : [{"number" :1,"age": 20, "testA": { "str" : "123"}},{"number" :2,"age": 21,"testA": {"str" : "456"}}]}'
    let jsonData: ESObject = JSON.parse(str)
    let responseObj: ResponseObj = plainToClass(ResponseObj, jsonData);
    console.log( `${responseObj.data[0] instanceof Person}`)
    this.list = this.list.concat(responseObj.data);
  }
  build() {
    Row() {
      Column() {
        ForEach(this.list, (item: Person, index: number) => {
          ViewA({ index: index, testA: item.testA })
        })
      }
      .width('100%')
    }
    .height('100%')
  }
}
@Observed
export class TestA {
  public str : string
  constructor(str: string) {
    this.str = str;
  }
}
export class Person {
  name: string = ''
  age: number = 1
  @Type(()=>TestA)
  testA: TestA = new TestA('')
}
@Component
export struct ViewA {
  @ObjectLink testA: TestA
  index: number = -1;
  build() {
    Row(){
      Button(`View A ${this.testA.str}`).onClick(() =>{
        this.index += 1;
        this.testA.str = `${this.index} : Test A String`
      })
    }.margin({top : 10 })
  }
}