HarmonyOS interface 问题

export interface IData{    }
1.

export class Data implements IData{  
  str:string = ''  
}
1.
2.
3.

Banner({  
  bannerOptions: $bannerOptions,  
  data: $data,  
  currentPosition:this.currentPosition,  
  bannerContent: (item : Data, index : number) => {  
    this.bannerContent(item, index)  
  }  
}).width('100%')  
  .height(132)
1.
2.
3.
4.
5.
6.
7.
8.
9.

export class Data implements IData{  
  str:string = ''  
} 
1.
2.
3.

"bannerContent: (item : Data, index : number) => "
1.