c# - 带有 Json 响应的 Http Post C#

Question

我想获得一个在 c# 中使用以下配置生成 http post 的方法。

  POST pqs.php HTTP/1.1
  Host: nationalmap.gov/epqs/pqs.php
  Content-Type: application/x-www-form-urlencoded
  Content-Length: length
  x=string&y=string&units=string&output=string

我尝试了以下方法，但是我得到了无效的坐标，尽管它们确实存在于 map 中(尝试的示例是 lat = 36.574832 和 lon = -85.411825

这是我使用的代码:

public class ElevationUSGISPull
{
    public string responseString = null;
    private string BASEURL = "http://nationalmap.gov/epqs/pqs.php";

    public bool httpPostElevationRequest( string lon,string lat)
    {

        try
        {
            using (WebClient client = new WebClient())
            {

                byte[] response =
                client.UploadValues(BASEURL, new NameValueCollection()
                {
                { "x", lon },
                { "y", lat },
                {"units", "feet" },
                {"output","json" },
                });

                string result = System.Text.Encoding.UTF8.GetString(response);
                responseString = result;
            }
            return true;
        }
        catch(Exception eX)
        {
            return false;
        }
    }
}

我得到的错误如下:

<error>General failure: Invalid Coordinates</error>

此外，是否有人尝试过 .gov 网站获取高程数据。我使用了谷歌服务器，但是它有很多与请求数量相关的限制，我正在尝试对给定区域进行许多请求。

下面是一个验证纬度和经度的网站，具有良好的 json 响应。

https://nationalmap.gov/epqs/

谢谢大家。

我在这里也试过下面的例子: http://ronaldrosiernet.azurewebsites.net/Blog/2013/12/07/posting_urlencoded_key_values_with_httpclient

但是给我以下错误。

Exception thrown: 'System.NullReferenceException'

我将代码修改为:

  public async Task<string> HTTPPOST(string lon, string lat)
    {
        var client = new HttpClient();
        client.BaseAddress = new Uri(BASEURL);
        var request = new HttpRequestMessage(HttpMethod.Post, "");

        var keyValues = new List<KeyValuePair<string, string>>();
        keyValues.Add(new KeyValuePair<string, string>("x", lon));
        keyValues.Add(new KeyValuePair<string, string>("y", lat));
        keyValues.Add(new KeyValuePair<string, string>("units", "feet"));
        keyValues.Add(new KeyValuePair<string, string>("output", "json"));

        request.Content = new FormUrlEncodedContent(keyValues);
        var response = await client.SendAsync(request);

        return response.ToString();
    }

Answer 1

调试一个小时后，我注意到我将单位作为参数而不是单位 :( ......

    public string httpPostElevationRequest( string lon,string lat)
    {
        try
        {
            using (WebClient client = new WebClient())
            {

                byte[] response =
                client.UploadValues(BASEURL, new NameValueCollection()
                {
                { "x", lon },
                { "y", lat },
                {"unit", "feet" },
                {"output","json" },
                });
                string result = System.Text.Encoding.UTF8.GetString(response);
                responseString = result;
            }
            return responseString;
        }
        catch(Exception eX)
        {
            return null;
        }
    }

还有baseurl如下:

private string BASEURL = "https://nationalmap.gov/epqs/pqs.php";