Xamarin Forms的问题从webservices/rest api检索json的问题

Question

我无法使用Xamarin表单中的PLC项目从webservice检索数据。 我已经尝试WebRequest和HttpClient，但得到各种例外。我也曾尝试 从这个样本运行代码：

1. ConnectFailure（网络无法访问）

   HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create ("http://localhost:3000/profile/contacts"); 
        webRequest.UseDefaultCredentials = true; 
        webRequest.Method = "GET"; 
        webRequest.Accept = "application/json"; 
        webRequest.ContentType = "application/json"; 
        webRequest.BeginGetResponse ((ar) => { 
         var request = (HttpWebRequest)ar.AsyncState; 
         try { 
          using (var response = (HttpWebResponse)request.EndGetResponse (ar)) {        
           var s = response.GetResponseStream(); 
          } 
         } catch (Exception ex) { 
          var xy = ex; 
         } 
   
        }, webRequest); 
   

2. ConnectFailure（请求的地址是无效在这种情况下）

     var client = new System.Net.Http.HttpClient(); 
         client.BaseAddress = new Uri("http://localhost:3000/"); 
         client.DefaultRequestHeaders.Clear(); 
         client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json")); 
         var response = await client.GetStringAsync ("profile/contacts"); 
   

我也试着运行这个示例中的代码：https://github.com/conceptdev/xamarin-forms-samples/tree/master/HttpClient/HttpClientDemo 尝试发出请求时会引发namesresolutionfail异常。

var client = new System.Net.Http.HttpClient(); 
       client.BaseAddress = new Uri("http://api.geonames.org/"); 
       var response = await client.GetAsync("earthquakesJSON?north=44.1&south=-9.9&east=-22.4&west=55.2&username=bertt"); 
       var earthquakesJson = response.Content.ReadAsStringAsync().Result; 
       var rootobject = JsonConvert.DeserializeObject<Rootobject>(earthquakesJson); 
       return rootobject.earthquakes; 

我测试了我的rest api（用Node.Js编写）并且它正在按照预期返回数据。

Answer 1

Eee，什么是localhost到Android？它不知道localhost实际上是你的电脑。根据api.geonames.org，这可能是一个模拟器问题。你在哪里测试你的应用程序？尝试真正的设备。