在UWP应用程序中使用HttpClient，需要第一次调用的结果，然后才能进行第二次调用

HttpClient httpClient = new HttpClient();

HttpResponseMessage response = await httpClient.GetAsync(url);
response.EnsureSuccessStatusCode();
string responseBody = await response.Content.ReadAsStringAsync();

HttpResponseMessage secondResponse = await httpClient.GetAsync(secondUrl);
secondResponse.EnsureSuccessStatusCode();
string secondResponseBody = await secondResponse.Content.ReadAsStringAsync();

httpClient.Dispose();