微软官方示例里的HTTPrequest借鉴

try
{
    HttpResponseMessage response = await httpClient.PostAsync(resourceAddress,
        new HttpStringContent(RequestBodyField.Text)).AsTask(cts.Token);

    await Helpers.DisplayTextResultAsync(response, OutputField, cts.Token);

    rootPage.NotifyUser("Completed", NotifyType.StatusMessage);
}
catch (TaskCanceledException)
{
    rootPage.NotifyUser("Request canceled.", NotifyType.ErrorMessage);
}
catch (Exception ex)
{
    rootPage.NotifyUser("Error: " + ex.Message, NotifyType.ErrorMessage);
}
finally
{
    Helpers.ScenarioCompleted(StartButton, CancelButton);
}

还借用另外两个CS文件：Helpers.cs / PlugInFilter.cs

但是在生成response时抛出exception

HttpResponseMessage response = await httpClient.PostAsync(resourceAddress,
    new HttpStringContent(RequestBodyField.Text)).AsTask(cts.Token);

09-25
在前期需要先定义变量

Helpers.CreateHttpClient(ref httpClient);
cts = new CancellationTokenSource();