har如何导出ArkUI组件？

// library/src/main/ets/components/mainpage/MainPage.ets
@Component
export struct MainPage {
@State message: string = 'HAR MainPage';

build() {
Column() {
Row() {
Text(this.message)
.fontSize(32)
.fontWeight(FontWeight.Bold)
}
.margin({ top: '32px' })
.height(56)
.width('624px')

Flex({ justifyContent: FlexAlign.Center, alignItems: ItemAlign.Center, alignContent: FlexAlign.Center }) {
Column() {
Image($r('app.media.pic_empty')).width('33%')
Text($r('app.string.empty'))
.fontSize(14)
.fontColor($r('app.color.text_color'))
}
}.width('100%')
.height('90%')
}
.width('100%')
.height('100%')
.backgroundColor($r('app.color.page_background'))
}
}

// library/Index.ets
export { MainPage } from './src/main/ets/components/mainpage/MainPage';