我建议您使用的 async-await 关键字，您可以像这样更改代码以获取结果：

what I would suggest to you is using the async-await keywords here, you can change your code like this to get the results:

HttpResponseMessage file = await httpclinet.GetAsync("url");
var stream = await file.Content.ReadAsStreamAsync()

此外，您还需要添加 async 关键字，例如：

Also you need to add the async keyword to your method like this:

public async Task<HttpResponseMessage> download(string fileid)