How can I use await with HttpWebRequest in Windows Phone 8 ?
Is there a way to make the IAsyncResult stuff work with await?
private async Task<int> GetCurrentTemperature()
{
GeoCoordinate location = GetLocation();
string url = "http://free.worldweatheronline.com/feed/weather.ashx?q=";
url += location.Latitude.ToString();
url += ",";
url += location.Longitude.ToString();
url += "&format=json&num_of_days=1&key=MYKEY";
HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(url);
webRequest.Method = "POST";
webRequest.BeginGetResponse(new AsyncCallback(OnGotWebRequest), webRequest);
}
private void OnGotWebRequest(IAsyncResult asyncResult)
{
HttpWebRequest webRequest = (HttpWebRequest)asyncResult.AsyncState;
var httpResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult);
using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
{
string responseText = streamReader.ReadToEnd();
}
}
Thanks!
Use TaskFactory.FromAsync to create a Task<Stream> from the BeginGetRequestStream/EndGetRequestStream methods. Then you can get rid of your OnGotWebRequest completely, and do the same thing for the response.
Note that currently you're calling EndGetResponse when a BeginGetRequestStream call completes, which is inappropriate to start with - you've got to call the EndFoo method to match the BeginFoo you originally called. Did you mean to call BeginGetResponse?
If you install the Microsoft.Bcl.Async package, you get a few async-ready extension methods, including ones for HttpWebRequest.
Related
I am new to silverlight. I am programming in Visual Studio 2010 for Windows phone.
I try to do HttpWebRequest but debugger says ProtocolViolationException.
This my code
private void log_Click(object sender, RoutedEventArgs e)
{
//auth thi is my url for request
string auth;
string login = Uri.EscapeUriString(this.login.Text);
string password = Uri.EscapeUriString(this.pass.Password);
auth = "https://api.vk.com/oauth/token";
auth += "?grant_type=password" + "&client_id=*****&client_secret=******&username=" + login + "&password=" + password + "&scope=notify,friends,messages";
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(auth);
request.BeginGetRequestStream(RequestCallBack, request);//on this line debager say ProtocolViolationExceptio
}
void RequestCallBack(IAsyncResult result)
{
HttpWebRequest request = result.AsyncState as HttpWebRequest;
Stream stream = request.EndGetRequestStream(result);
request.BeginGetResponse(ResponceCallBack, request);
}
void ResponceCallBack(IAsyncResult result)
{
HttpWebRequest request = result.AsyncState as HttpWebRequest;
HttpWebResponse response = request.EndGetResponse(result) as HttpWebResponse;
using (StreamReader sr = new StreamReader(response.GetResponseStream()))
{
string a =sr.ReadToEnd();
MessageBox.Show(a);
}
}
I think the problem is that you aren't using POST, but GET. Try this:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(auth);
request.Method = "POST";
request.BeginGetRequestStream(RequestCallBack, request);
You aren't even doing anything with the request stream when you get it.
HttpWebRequest is assuming that the reason you tried to get it, was to write content to it (the only reason for getting it, after all).
Since you aren't allowed to include content in a GET request, it realises that the only thing you can do with that stream, is something that would violate the HTTP protocol. As a tool for using the HTTP protocol, it's its job to stop you making that mistake.
So it throws ProtocolViolationException.
Cut out the bit about the request stream - it's only for POST and PUT. Go straight to GetResponse() or BeginGetResponse() at that point.
I'm trying to use the Azure media services with REST api, in a xamarin shared project on visual studio 2013. This is the code i use to get the access token.
public HttpFactory()
{
string token = GetToken(serviceURI).Result;
//some more methods also async tasks
}
private async Task<string> GetToken(Uri serviceUri)
{
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(serviceURI);
request.Accept = "application/json";
request.Method = "GET";
request.Headers["Host"] = "media.windows.net";
request.Headers["x-ms-version"] = "2.9";
request.Headers["Authorization"] = "Bearer " + token;
var response = (HttpWebResponse) await request.GetResponseAsync();
if (response.StatusCode == HttpStatusCode.MovedPermanently)
{
serviceURI = new Uri(response.Headers["Location"]);
HttpWebRequest req = ( HttpWebRequest)WebRequest.Create(serviceURI);
var res = (HttpWebResponse)await req.GetResponseAsync();
using (Stream responseStream = res.GetResponseStream())
{
using (StreamReader reader = new StreamReader(responseStream))
{
string str = reader.ReadToEnd();
// var test = JsonConvert.DeserializeObject(str);
JToken jtoken = JsonConvert.DeserializeObject<JToken>(str);
return jtoken["access_token"].Value<string>();
}
}
}
return "";
}
But when the compiler reaches -
var response = (HttpWebResponse) await request.GetResponseAsync();
it skips the rest of the code, and i never get the response. I know the code is working - because it works just fine without the task, in a async void method.
Anyone knows how to fix this, or am i doing something wrong? I also tried this in vs2015 but its the same.
You have a deadlock over the UI thread.
You're blocking the thread with Task.Result when it is needed to complete the async method which will complete the task that it's waiting on.
That's why you shouldn't block synchronously on asynchronous code. You should await the task returned from GetToken instead:
string token = await GetToken(serviceURI);
If you can't use async in that method, either move that logic to a different method (e.g. OnLoad event handler).
Another solution would be to use ConfigureAwait on the GetResponseAsync task and so the rest of the method wouldn't run on the UI thread, avoiding the deadlock:
var response = (HttpWebResponse) await request.GetResponseAsync().ConfigureAwait(false);
I want to send a post request to an API with some parameters they ask for... I ended up just creating a string, it's ugly but I do not know a way of making it work differently. I then found lots of variations on this WebRequest class, but unfortunately I cannot get it to work.
Main problem is probably because I am not really understanding how this is all fitting together but basically, the examples I have been following use WebRequest method GetResponse... even on MSDN it has this, so I am wondering why when I try to call it in my code, I am not getting that choice? Same goes for GetRequestStream.
How to add parameters into a WebRequest?
*****DBContext()
{
data = "grant_type=" + GRANTTYPE + "&username=" + username + "&password=" + password + "&client_id=" + CLIENTID + "&redirect_uri=" + REDIRECTURI + "&client_secret=" + CLIENTSECRET;
}
public bool Authenticate()
{
byte[] dataStream = Encoding.UTF8.GetBytes(data);
WebRequest webRequest = WebRequest.Create(urlPath);
webRequest.Method = "POST";
webRequest.ContentType = "application/json";
webRequest.ContentLength = dataStream.Length;
Stream newStream = webRequest.GetRequestStream();
// Send the data.
newStream.Write(dataStream, 0, dataStream.Length);
newStream.Close();
WebResponse webResponse = webRequest.GetResponse();
return true;
}
I also have the question of when I finally do get this stuff to work, what should I be putting in the callback uri. if it's a phone, is it running off of localhost?
The .NET compilation for Windows Phone contains an implementation of the WebRequest class which does not have synchronous methods for obtaining request stream and response, as these would block execution on the UI thread until the operations completed. You can use the existing Begin/End methods directly with callback delegates, or you can wrap those calls in async extensions that will give you the kind of readability and functionality you're used to (more or less). My preferred method is defining extensions, so I will demonstrate this method, but it has no performance advantage over the callback pattern. It does have the up-side of being easily portable any time you need to make use of a WebRequest.
Async/Await Pattern
Define custom extensions for the WebRequest class:
public static class Extensions
{
public static System.Threading.Tasks.Task<System.IO.Stream> GetRequestStreamAsync(this System.Net.WebRequest wr)
{
if (wr.ContentLength < 0)
{
throw new InvalidOperationException("The ContentLength property of the WebRequest must first be set to the length of the content to be written to the stream.");
}
return Task<System.IO.Stream>.Factory.FromAsync(wr.BeginGetRequestStream, wr.EndGetRequestStream, null);
}
public static System.Threading.Tasks.Task<System.Net.WebResponse> GetResponseAsync(this System.Net.WebRequest wr)
{
return Task<System.Net.WebResponse>.Factory.FromAsync(wr.BeginGetResponse, wr.EndGetResponse, null);
}
}
Use the new extensions (be sure to import the namespace where your static Extensions class was defined):
public async System.Threading.Tasks.Task<bool> AuthenticateAsync()
{
byte[] dataStream = System.Text.Encoding.UTF8.GetBytes("...");
System.Net.WebRequest webRequest = System.Net.WebRequest.Create("...");
webRequest.Method = "POST";
webRequest.ContentType = "application/json";
webRequest.ContentLength = dataStream.Length;
Stream newStream = await webRequest.GetRequestStreamAsync();
// Send the data.
newStream.Write(dataStream, 0, dataStream.Length);
newStream.Close();
var webResponse = await webRequest.GetResponseAsync();
return true;
}
Regarding your final note, at the moment I don't see enough information to make sense of what the callback URI is, where it's defined, and how it affects what you're doing.
I am new to silverlight. I am programming in Visual Studio 2010 for Windows phone.
I try to do HttpWebRequest but debugger says ProtocolViolationException.
This my code
private void log_Click(object sender, RoutedEventArgs e)
{
//auth thi is my url for request
string auth;
string login = Uri.EscapeUriString(this.login.Text);
string password = Uri.EscapeUriString(this.pass.Password);
auth = "https://api.vk.com/oauth/token";
auth += "?grant_type=password" + "&client_id=*****&client_secret=******&username=" + login + "&password=" + password + "&scope=notify,friends,messages";
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(auth);
request.BeginGetRequestStream(RequestCallBack, request);//on this line debager say ProtocolViolationExceptio
}
void RequestCallBack(IAsyncResult result)
{
HttpWebRequest request = result.AsyncState as HttpWebRequest;
Stream stream = request.EndGetRequestStream(result);
request.BeginGetResponse(ResponceCallBack, request);
}
void ResponceCallBack(IAsyncResult result)
{
HttpWebRequest request = result.AsyncState as HttpWebRequest;
HttpWebResponse response = request.EndGetResponse(result) as HttpWebResponse;
using (StreamReader sr = new StreamReader(response.GetResponseStream()))
{
string a =sr.ReadToEnd();
MessageBox.Show(a);
}
}
I think the problem is that you aren't using POST, but GET. Try this:
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(auth);
request.Method = "POST";
request.BeginGetRequestStream(RequestCallBack, request);
You aren't even doing anything with the request stream when you get it.
HttpWebRequest is assuming that the reason you tried to get it, was to write content to it (the only reason for getting it, after all).
Since you aren't allowed to include content in a GET request, it realises that the only thing you can do with that stream, is something that would violate the HTTP protocol. As a tool for using the HTTP protocol, it's its job to stop you making that mistake.
So it throws ProtocolViolationException.
Cut out the bit about the request stream - it's only for POST and PUT. Go straight to GetResponse() or BeginGetResponse() at that point.
I have been using the following code to obtain a simple web response from Apache 2.2 in SilverLight to no avail.
private void bDoIt_Click(object sender, RoutedEventArgs e)
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(new Uri("/silverlight/TestPage2.html"));
request.Method = "POST";
request.ContentType = "text/xml";
request.BeginGetRequestStream(new AsyncCallback(RequestProceed), request);
}
private void RequestProceed(IAsyncResult asuncResult)
{
HttpWebRequest request = (HttpWebRequest)asuncResult.AsyncState;
StreamWriter postDataWriter = new StreamWriter(request.EndGetRequestStream(asuncResult));
postDataWriter.Close();
request.BeginGetResponse(new AsyncCallback(ResponceProceed), request);
}
private void ResponceProceed(IAsyncResult asuncResult)
{
HttpWebRequest request = (HttpWebRequest)asuncResult.AsyncState;
HttpWebResponse responce = (HttpWebResponse)request.EndGetResponse(asuncResult);
StreamReader responceReader = new StreamReader(responce.GetResponseStream());
string responceString = responceReader.ReadToEnd();
txtData.Text = responceString;
}
Does anyone no a better method of doing this?
Have you tried WebClient? This exists on silverlight, and might make life easier. Presumably you'd want UploadStringAsync.
Also - I believe you need to use and absolute url; if you don't want to hard code (quite reasonably), you can get your host from:
string url = App.Current.Host.Source.AbsoluteUri;
Then use string / etc methods to make the correct "http://yoursite/whatever/your.page";
Note that silverlight only allows (IIRC) connections to the host site.
You can do the BeginGetResponse call as the first call in your sample test case, the BeginGetRequestStream call is only needed if you are intending to pass some POST data to the requested page.