HttpWebRequest BeginGetResponse EndGetResponse

        private void Button_Click_4(object sender, RoutedEventArgs e)
        {
            HttpWebRequest request = HttpWebRequest.CreateHttp("http://www.example.com");
            //request.Headers["UserAgent"]
            request.Method = "GET";
            request.BeginGetResponse(callback, request);
        }

        private async void callback(IAsyncResult asyncResult)
        {
            //var httpWebResponse = request.EndGetResponse(asyncResult) as HttpWebRequest;
            var request = asyncResult.AsyncState as HttpWebRequest;
            var response = request.EndGetResponse(asyncResult);
            Stream stream = response.GetResponseStream();
            StreamReader reader = new StreamReader(stream, System.Text.Encoding.UTF8);
            string json = reader.ReadToEnd();
            await this.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
            {
                txtResult.Text = json;
            });

        }

        private void Button_Click_4(object sender, RoutedEventArgs e)
        {
            HttpWebRequest request = HttpWebRequest.CreateHttp("http://www.example.com");
            //request.Headers["UserAgent"]
            request.Method = "GET";
            request.BeginGetResponse(async (asyncResult) =>
            {
                //var httpWebResponse = request.EndGetResponse(asyncResult) as HttpWebRequest;
                var response = request.EndGetResponse(asyncResult);
                Stream stream = response.GetResponseStream();
                StreamReader reader = new StreamReader(stream, System.Text.Encoding.UTF8);
                string json = reader.ReadToEnd();
                await this.Dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =>
                {
                    txtResult.Text = json;
                });
            }, request);
        }