关于写wp api中的问题

直接上代码
未提供与“HttpWebRequest.BeginGetResponse(AsyncCallback, object)”的必需形参“state”对应的实参 danteng E:\danteng\danteng\zhanji.xaml.cs 50

求大神解答

private void chaxunbutton1_Click(object sender, RoutedEventArgs e)
{
{
string resultString = textBox1.Text;
HttpWebRequest request = HttpWebRequest.CreateHttp("http://300report.jumpw.com/api/getrole?name=");
request.Method = "GET";

            request.BeginGetResponse((IAsyncResult) =>
            {
                HttpWebRequest webRequest = result.AsyncState as HttpWebRequest;
                HttpWebResponse webResponse = (HttpWebResponse)webRequest.EndGetResponse(result);
                Stream streamResult = webResponse.GetResponseStream();
                StreamReader reader = new StreamReader(streamResult);

                resultString = reader.ReadToEnd();

                JObject jo = (JObject)JsonConvert.DeserializeObject(jsonstr);



                if (jo["Result"].ToString() == "OK")
                {
                    textBlock1.Text = ("角色名称：" + jo["Role"]["RoleName"].ToString());
                    textBlock2.Text = ("角色等级：" + jo["Role"]["RoleLevel"].ToString());
                    textBlock3.Text = ("节操值：" + jo["Role"]["JumpValue"].ToString());
                    textBlock4.Text = ("胜场数：" + jo["Role"]["WinCount"].ToString());
                    textBlock5.Text = ("总场数：" + jo["Role"]["MatchCount"].ToString());
                }
                else
                {
                    textBlock3.Text = ("读取英雄信息失败！");
                }



            });
        } }
        }
    }