HarmonyOS 鸿蒙Next怎么打开读取下载内容路径下的文件

要读取sdcard/download路径下的文件可能需要降到api 8。
通过api 8 的媒体库的方法可以读取到相关路径，然后获取目标路径的fd；

然后用fd去 fileio 模块调用相关路径解析文件，但是有个问题我没有办法解决，就是下面例子里的open方法属于媒体库下的方法，好像只能打开媒体资源，例如png、jpg等文件。我是直接将把png文件当成文本文件读取的，暂时没发现问题；

let media = mediaLibrary.getMediaLibrary();
// 创建文件获取选项，此处参数为获取image类型的文件资源
    let imagesFetchOp = {
      // selections: fileKeyObj.MEDIA_TYPE + '= ?',
      selections: mediaLibrary.FileKey.ALBUM_NAME + '= ?',
      selectionArgs: ["Download"],
    };
<span class="hljs-comment"><span class="hljs-comment">// 获取文件资源，使用callback方式返回异步结果</span></span>
media.getFileAssets(imagesFetchOp, async (error, fetchFileResult) =&gt; {
  <span class="hljs-comment"><span class="hljs-comment">// 获取文件检索结果集中的总数</span></span>
  <span class="hljs-keyword"><span class="hljs-keyword">const</span></span> count = fetchFileResult.getCount();
  console.info(<span class="hljs-string"><span class="hljs-string">'日志：检索内容数量:'</span></span> + count);
  <span class="hljs-comment"><span class="hljs-comment">// 判断结果集中的数量是否小于0，小于0时表示接口调用失败</span></span>
  <span class="hljs-keyword"><span class="hljs-keyword">if</span></span> (count &lt;= <span class="hljs-number"><span class="hljs-number">0</span></span>) {
    console.error(<span class="hljs-string"><span class="hljs-string">'日志：检索异常, count: '</span></span> + count);
    <span class="hljs-keyword"><span class="hljs-keyword">return</span></span>;
  }
  fetchFileResult.getAllObject(async (err, fileAssetList) =&gt; {
    <span class="hljs-keyword"><span class="hljs-keyword">if</span></span> (err) {
      console.error(<span class="hljs-string"><span class="hljs-string">'日志：Failed '</span></span>);
      <span class="hljs-keyword"><span class="hljs-keyword">return</span></span>;
    }
    <span class="hljs-keyword"><span class="hljs-keyword">for</span></span> (<span class="hljs-keyword"><span class="hljs-keyword">let</span></span> i = <span class="hljs-number"><span class="hljs-number">0</span></span>; i &lt; count; i++) {
      <span class="hljs-comment"><span class="hljs-comment">// console.log('日志: fileAsset.displayName : ' + fileAssetList[i].displayName);</span></span>
      <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> fileAsset = fileAssetList[i];
      console.info(<span class="hljs-string"><span class="hljs-string">'日志：[fileAsset.displayName] '</span></span> + i + <span class="hljs-string"><span class="hljs-string">': '</span></span> + fileAsset.displayName);
      <span class="hljs-keyword"><span class="hljs-keyword">if</span></span> (fileAsset.displayName === <span class="hljs-string"><span class="hljs-string">"userList.bmp"</span></span>) {
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> fd = await fileAsset.open(<span class="hljs-string"><span class="hljs-string">'r'</span></span>)
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> stream = fileio.fdopenStreamSync(fd, <span class="hljs-string"><span class="hljs-string">'r'</span></span>)
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> readOut = await stream.read(<span class="hljs-keyword"><span class="hljs-keyword">new</span></span> <span class="hljs-built_in"><span class="hljs-built_in">ArrayBuffer</span></span>(<span class="hljs-number"><span class="hljs-number">10000000</span></span>));
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> textDecoder = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> util.TextDecoder(<span class="hljs-string"><span class="hljs-string">"utf-8"</span></span>, { ignoreBOM: <span class="hljs-literal"><span class="hljs-literal">true</span></span> });
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> buffer = <span class="hljs-keyword"><span class="hljs-keyword">new</span></span> <span class="hljs-built_in"><span class="hljs-built_in">Uint8Array</span></span>(readOut.buffer)
        <span class="hljs-keyword"><span class="hljs-keyword">let</span></span> readString = textDecoder.decode(buffer, { stream: <span class="hljs-literal"><span class="hljs-literal">false</span></span> });
        console.info(<span class="hljs-string"><span class="hljs-string">"日志：[userList]"</span></span> + readString.replace(<span class="hljs-regexp"><span class="hljs-regexp">/[\n\r]+/g</span></span>, <span class="hljs-string"><span class="hljs-string">""</span></span>))
      }
    }
  })
});</code><button style="position: absolute; padding: 4px 8px 0px; cursor: pointer; top: 8px; right: 8px; font-size: 14px;">复制</button></pre></div></div>