对象取值在api10中不支持这样取值 listItem[item]，只能json 转两次

type typeA = Record<string, string> 
class A { 
  typeA: typeA = { 
    'str': 'a', 
    'str2': 'b' 
  } 
} 
@Entry 
@Component 
struct Test { 
  @State message: string = 'Hello World' 
  @State A: A = new A() 
  @State str: string = 'str' 
  test() { 
    console.info((this.A.typeA[this.str])) 
  } 
  build() { 
    Row() { 
      Column() { 
        Text(this.message) 
          .fontSize(50) 
          .fontWeight(FontWeight.Bold) 
          .onClick(() => { 
            this.test() 
          }) 
      } 
      .width('100%') 
    } 
    .height('100%') 
  } 
}