xamarin android webservice出错

Question

我使用下面的代码创建php mys1l webservice，当运行应用程序时出现异常错误，服务器返回错误404并且调试器指向此行：

var response = client.UploadValues(uri, parameters);

我的完整代码

            WebClient client = new WebClient();

            Uri uri = new Uri("http://149.255.62.48/Login/xamarinsignIn.php");


            NameValueCollection parameters = new NameValueCollection();
            parameters.Add("uemail", userEmail);
            parameters.Add("pass", userPassword);
            var response = client.UploadValues(uri, parameters);
            var responseString = Encoding.Default.GetString(response);
            JSONObject ob = new JSONObject(responseString);
            if (ob.OptString("success").Equals("1"))
            {


                mainActivity.RunOnUiThread(() =>
                Toast.MakeText(mainActivity, "You Successfully LogIn", ToastLength.Short).Show());
            }
            else {
                mainActivity.RunOnUiThread(() =>
                                           Toast.MakeText(mainActivity, "InValid Email or Password", ToastLength.Short).Show());

            }