HarmonyOS interface 问题

export interface IData{    }

export class Data implements IData{  
  str:string = ''  
}

Banner({  
  bannerOptions: $bannerOptions,  
  data: $data,  
  currentPosition:this.currentPosition,  
  bannerContent: (item : Data, index : number) => {  
    this.bannerContent(item, index)  
  }  
}).width('100%')  
  .height(132)

export class Data implements IData{  
  str:string = ''  
} 

"bannerContent: (item : Data, index : number) => "