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);
}