HarmonyOS 如何将Resource资源类型，转换为文件所在的路径string？

import photoAccessHelper from '@ohos.file.photoAccessHelper'; 
import fs from '@ohos.file.fs'; 
import common from '@ohos.app.ability.common'; 
import promptAction from '@ohos.promptAction'; 
import { BusinessError } from '@ohos.base'; 
async function savePhotoToGallery(context: common.UIAbilityContext) { 
  let helper = photoAccessHelper.getPhotoAccessHelper(context); 
  try { 
    // onClick触发后5秒内通过createAsset接口创建图片文件，5秒后createAsset权限收回。 
    let uri = await helper.createAsset(photoAccessHelper.PhotoType.IMAGE, 'jpg'); 
    // 使用uri打开文件，可以持续写入内容，写入过程不受时间限制 
    let file = await fs.open(uri, fs.OpenMode.READ_WRITE | fs.OpenMode.CREATE); 
    context.resourceManager.getMediaContent($r('app.media.bg1').id, 0) 
      .then(async value => { 
        let media = value.buffer; 
        // 写到媒体库文件中 
        await fs.write(file.fd, media); 
        await fs.close(file.fd); 
        promptAction.showToast({ message: '已保存至相册！' }); 
      }); 
  } 
  catch (error) { 
    const err: BusinessError = error as BusinessError; 
    console.error(Failed to save photo. Code is ${err.code}, message is ${err.message}); 
  } 
} 
@Entry 
@Component 
struct Index { 
  build() { 
    Row() { 
      Column({ space: 10 }) { 
        Image($r('app.media.bg1')) 
          .height(400) 
          .width('100%') 
          .draggable(false) 
    SaveButton().onClick(async (event: ClickEvent, result: SaveButtonOnClickResult) => { 
      if (result === SaveButtonOnClickResult.SUCCESS) { 
        const context: common.UIAbilityContext = getContext(this) as common.UIAbilityContext; 
        savePhotoToGallery(context); 
      } else { 
        promptAction.showToast({ message: '设置权限失败！' }) 
      } 
    }) 
  } 
  .width('100%') 
} 
.height('100%') 
.backgroundColor(0xF1F3F5) 
  } 
}