当互联网断开连接时，HttpClient PostAsync 不响应

我有一个 xamarin 表单应用程序，该应用程序执行PostAsync调用将图像作为多部分内容上传。

问题是在 iOS 设备中，当我在 PostAsync 调用期间关闭 wifi/移动数据时，HttpClient 不会进入 catch 块来指示异常。它仅在默认的 100 秒超时后才会执行此操作。

但是Android中不会出现这个问题，并且成功进入catch块，表明System.IO.IOException

这是我的代码，它执行PostAsync打电话，我错过了什么或者做错了什么吗？谢谢。

 try{
 MultipartFormDataContent multipartContent = new MultipartFormDataContent();
 var uri = new Uri(string.Format(strUrl + "UserData/SavePointRequestData/", string.Empty));

 StringContent strPointsRequestIDContent = new StringContent(oPointRequest.PointsRequestID.ToString());
 multipartContent.Add(strPointsRequestIDContent, "strPointsRequestID");
 if (bImageData != null) {
  var PointRequestfileContent = new ByteArrayContent(bImageData);
  PointRequestfileContent.Headers.ContentType = MediaTypeHeaderValue.Parse("application/octet-stream");
  PointRequestfileContent.Headers.ContentDisposition = new ContentDispositionHeaderValue("form-data") {
   FileName = strActualImageName + ".jpg"
  };
  multipartContent.Add(PointRequestfileContent, "strUploadImage");
 }

 HttpClient client = new HttpClient();
 HttpResponseMessage response = await client.PostAsync(uri, multipartContent);
 if (response.IsSuccessStatusCode) {
  using(var stream = await response.Content.ReadAsStreamAsync()) {
   using(var streamreader = new StreamReader(stream)) {
    var str = await streamreader.ReadToEndAsync();
    var obj = await JsonConvert.DeserializeObjectAsync < string > (str);
    return obj;
   }
  }
 } else {
  return "Error1" + "," + oPointRequest.EventActivityName.ToString();
 }
 } 
catch (Exception ex) {
  System.Diagnostics.Debug.WriteLine(e.Message);


  return "Error2" + "," + oPointRequest.EventActivityName.ToString();
 }