HarmonyOS 保存PixelMap到相册，显示保存成功，相册中的图片为空白图片，宽高都是0

可以参考：

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 { image } from '@kit.ImageKit';

@Entry
@Component
struct Index {
  @State icon: image.PixelMap | undefined = undefined;

  build() {
    Row() {
      Column({ space: 10 }) {
        SaveButton().onClick(async (event: ClickEvent, result: SaveButtonOnClickResult) => {
          if (result === SaveButtonOnClickResult.SUCCESS) {
            const context: common.UIAbilityContext =
              getContext(this) as common.UIAbilityContext; // 免去权限申请和权限请求等环节，获得临时授权，保存对应图片
            this.savePhotoToGallery(context);
          } else {
            promptAction.showToast({ message: '设置权限失败！' })
          }
        })
      }.width('100%')
    }.height('100%').backgroundColor(0xF1F3F5)
  }

  async savePhotoToGallery(context: common.UIAbilityContext) {
    const imagePackerApi: image.ImagePacker = image.createImagePacker();
    const color: ArrayBuffer =
      new ArrayBuffer(96); // 96为需要创建的像素buffer大小，取值为：height * width *4
    let opts: image.InitializationOptions = { editable: true, pixelFormat: 3, size: { height: 4, width: 6 } }
    this.icon = await image.createPixelMap(color, opts);
    image.createPixelMap(color, opts).then((pixelMap: image.PixelMap) => {
      let packOpts: image.PackingOption = { format: "image/jpeg", quality: 98 }
      imagePackerApi.packing(pixelMap, packOpts).then(async (buffer: ArrayBuffer) => {
        console.info('Succeeded in packing the image.');
        let helper = photoAccessHelper.getPhotoAccessHelper(context)
        let uri = await helper.createAsset(photoAccessHelper.PhotoType.IMAGE,
          'png') // 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)
        try {
          context.resourceManager.getMediaContent($r('app.media.startIcon').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 (err) {
          console.error("error is "+ JSON.stringify(err))
        }
      })
    })
  }
}
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