组件要使用 @Component 装饰器定义；

// library/src/main/ets/components/MyTitleBar.ets
@Component
export struct MyTitleBar {
  build() {
    Row() {
      Text($r('app.string.library_title'))
        .id('library')
        .fontFamily('HarmonyHeiTi')
        .fontWeight(FontWeight.Bold)
        .fontSize(32)
        .fontColor($r('app.color.text_color'))
    }
    .width('100%')
  }
}

调用：

export { MyTitleBar } from './src/main/ets/components/MyTitleBar';