关于 Extend 使用问题

// CommonAttribute.ets  
export class TitleTextAttribute implements AttributeModifier<TextAttribute> {  
  applyNormalAttribute(instance: TextAttribute): void {  
    instance.backgroundColor(Color.Black)  
    instance.fontColor(Color.White)  
    instance.fontSize(40)  
  }  
}  
  
// Index.ets  
import { TitleTextAttribute } from './CommonAttribute'  
  
@Entry  
@Component  
struct Index {  
  @State modifier: TitleTextAttribute = new TitleTextAttribute()  
  build() {  
    Row() {  
      Column() {  
        Text('Hello World')  
          .attributeModifier(this.modifier)  
      }  
      .width('100%')  
    }  
    .height('100%')  
  }  
}