如何实现应用数据持久化存储

AppStorage.link('varA') 
PersistentStorage.persistProp("varA", "111"); 
 
@Entry 
@Component 
struct Index { 
  @StorageLink('varA') varA: string = '' 
 
  build() { 
    Column() { 
      Text('varA: ' + this.varA).fontSize(20) 
      Button('Set').width(100).height(100).onClick(() => { 
        this.varA += '333' 
      }) 
    } 
    .width('100%') 
    .height('100%') 
  } 
}