In a callback method I am attempting to get the text property of a textBox like this:
string postData = tbSendBox.Text;
But because its not executed on the UI thread it gives me a cross-thread exception.
I want something like this:
Dispatcher.BeginInvoke(() =>
{
string postData = tbSendBox.Text;
});
But this runs asynchronously. The synchronous version is:
Dispatcher.Invoke(() =>
{
string postData = tbSendBox.Text;
});
But Dispatcher.Invoke() does not exist for the Windows Phone. Is there something equivalent? Is there a different approach?
Here is the whole function:
public void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
Stream postStream = request.EndGetRequestStream(asynchronousResult);
string postData = tbSendBox.Text;
// Convert the string into a byte array.
byte[] byteArray = Encoding.UTF8.GetBytes(postData);
// Write to the request stream.
postStream.Write(byteArray, 0, postData.Length);
postStream.Close();
// Start the asynchronous operation to get the response
request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
}
No you are right you can access only to the async one. Why do you want sync since you are on a different thread of the UI one?
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
string postData = tbSendBox.Text;
});
This should make an asynchronous call to a synchronous :
Exception exception = null;
var waitEvent = new System.Threading.ManualResetEvent(false);
string postData = "";
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
try
{
postData = tbSendBox.Text;
}
catch (Exception ex)
{
exception = ex;
}
waitEvent.Set();
});
waitEvent.WaitOne();
if (exception != null)
throw exception;
1) Obtain a reference to the synchronization context of UI thread. For example,
SynchronizationContext context = SynchronizationContext.Current
2) Then post your callback to this context. This is how Dispatcher internally works
context.Post((userSuppliedState) => { }, null);
Is it what you want?
Related
We were developing a sample MWC application with the logic of Business ,DataAccess,Data Layers.
In core Project we used the following code for consuming data from json parsing. This code works fine for Xamarin.Android and Xamarin.iOS, but for windows phone it shows error as 'System.Net.WebRequest does not contain a definition for GetResponse and no extension method for GetResponse...'
We tried to use Async methods for consuming WCF Rest service json data, but it returned as null before the completed method called.
Is it possible to wait and get data from completed method to return the json collection? if no please suggest how to achieve the same.
public String login<T>(T item) where T : BusinessLayer.Contracts.IBusinessEntity, new()
{
var request = HttpWebRequest.Create(url);
request.ContentType = "application/json";
request.Method = "get";
using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
{
using (StreamReader reader = new StreamReader(response.GetResponseStream()))
{
var content = reader.ReadToEnd();
string nss = content.ToString();
check = nss;
return nss;
}
}
return Check;
}
Edit: I have included the sample code of Async function.
Before Executing the DownloadStringCompleted event it returns null value. We need that DownloadStringCompleted output string for further process.
Note: We were following the logic of Tasky in Xamarin
async Task<string> AccessTheWebAsync(string url)
{
var webClient = new WebClient();
webClient.DownloadStringCompleted += (sender, e) =>
{
string data = (string)e.Result;
check = data;
};
webClient.DownloadStringAsync(new Uri(url));
return check;
}
public async Task<string> login<T>(T item) where T : BusinessLayer.Contracts.IBusinessEntity, new()
{
return check = await AccessTheWebAsync(item.url);
}
Your asynchronous code is not using Task correctly. It should use TaskCompletionSource to get the job done:
Task<string> AccessTheWebAsync(string url)
{
var source = new TaskCompletionSource<string>();
var webClient = new WebClient();
webClient.DownloadStringCompleted += (sender, e) =>
{
source.TrySetResult((string)e.Result);
};
webClient.DownloadStringAsync(new Uri(url));
return source.Task;
}
Before, your function was returning before the event fired. Using the task source wraps it in a task properly and fixes this problem.
You will also need to hook up the error event and call TrySetException to finish the implementation.
void GetResponseCallback(IAsyncResult asynchronousResult)
{
try
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
Stream streamResponse = response.GetResponseStream();
StreamReader streamRead = new StreamReader(streamResponse);
string responseString = streamRead.ReadToEnd();
XmlReader xmlDoc = XmlReader.Create(new MemoryStream(System.Text.UTF8Encoding.UTF8.GetBytes(responseString)));
while (xmlDoc.Read())
{
if (xmlDoc.NodeType == XmlNodeType.Element)
{
if (xmlDoc.Name.Equals("ResponseCode"))
{
responseCode = xmlDoc.ReadInnerXml();
}
}
}
if (Convert.ToInt32(responseCode) == 200)
{
MessageBox.Show("Success");
}
// Close the stream object
streamResponse.Close();
streamRead.Close();
// Release the HttpWebResponse
response.Close();
}
catch (WebException e)
{
// Error treatment
// ...
}
}
in above code Messagebox.show dispalying "Invalid cross thread access".please tell me how to resolve this...
Dispatcher.BeginInvoke(() =>
MessageBox.Show("Your message")
);
Any interaction with the UI from code needs to be on the dispatcher thread, your callback from the HTTP request will not be running on this thread hence the error.
You should be able to use something like
Deployment.Current.Dispatcher.BeginInvoke(() => MessageBox.SHow("Success") );
to display the message box
HTH - Rupert.
I'm trying to validate a user in my WP7 app by validating username/pass on a server.
In my "validate user" method I create a HTTPWebRequest with the stuff I need validated.
Then as far as I can see, the only option to execute is to use request.BeginGetResponse, with an async callback.
But I want to return the response from the request in the same method that I created the request in, how can I accomplish this?
I'm not sure why you would like to make it return in the calling method. I would just use the standard WebClient behavior like below:
public void ValidateUser()
{
WebClient webClient = new WebClient();
Uri uri = new Uri(url);
webClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(webClient_DownloadStringCompleted);
webClient.DownloadStringAsync(new Uri(url));
}
void webClient_DownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e)
{
//Validate result from response by using e.Result
}
BeginGetResponse returns an IAsyncResult which has a wait handle that is signalled when the request completes. All you have to do is wait on this handle: [ doesn't work on WP7 ]
UPDATE: use a ManualResetEvent
var mre = new ManualResetEvent( false );
var iar = myHttpWebRequest.BeginGetResponse( state => mre.Set(), null );
mre.WaitOne();
var response = myHttpWebRequest.EndGetResponse( iar );
The only real way to achieve what you need would be to create an event in your worker class, and fire that event when the async call completes, so (pseudocode)...
void StartDownload(object[] parameters)
{
var req = HttpWebRequest.Create("http://google.com");
req.BeginGetRequestStream(Completed_handler, req);
}
void Completed_handler(object sender, DownloadStringCompletedEventArgs e)
{
var request = (HttpWebRequest)result.AsyncState;
var response = request.EndGetResponse(result);
using (var stream = response.GetResponseStream())
using (var reader = new StreamReader(stream))
{
var contents = reader.ReadToEnd();
NotifyCallerOfContent(contents)
}
}
public event EventHandler<MyCustomEventArgsClass> DownloadHasFinished;
public NotifyCallerOfDownload(string content)
{
if(null != DownloadHasFinished)
{
DownloadHasFinished(this, new MyCustomEventArgsClass(content));
}
}
and then subscribe to the DownloadHasFinished event in your calling class.
As for calling out specifically by a HttpWebRequest, take a look at this question, where you will find some working samples.
I found an example about HTTP POST in msdn, but I am wondering how can I make use of reactive extensions here.
using System;
using System.Net;
using System.IO;
using System.Text; using System.Threading;
class HttpWebRequestBeginGetRequest
{
private static ManualResetEvent allDone = new ManualResetEvent(false);
public static void Main(string[] args)
{
// Create a new HttpWebRequest object.
HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://www.contoso.com/example.aspx");
request.ContentType = "application/x-www-form-urlencoded";
// Set the Method property to 'POST' to post data to the URI.
request.Method = "POST";
// start the asynchronous operation
request.BeginGetRequestStream(new AsyncCallback(GetRequestStreamCallback), request);
// Keep the main thread from continuing while the asynchronous
// operation completes. A real world application
// could do something useful such as updating its user interface.
allDone.WaitOne();
}
private static void GetRequestStreamCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
Stream postStream = request.EndGetRequestStream(asynchronousResult);
Console.WriteLine("Please enter the input data to be posted:");
string postData = Console.ReadLine();
// Convert the string into a byte array.
byte[] byteArray = Encoding.UTF8.GetBytes(postData);
// Write to the request stream.
postStream.Write(byteArray, 0, postData.Length);
postStream.Close();
// Start the asynchronous operation to get the response
request.BeginGetResponse(new AsyncCallback(GetResponseCallback), request);
}
private static void GetResponseCallback(IAsyncResult asynchronousResult)
{
HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
// End the operation
HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
Stream streamResponse = response.GetResponseStream();
StreamReader streamRead = new StreamReader(streamResponse);
string responseString = streamRead.ReadToEnd();
Console.WriteLine(responseString);
// Close the stream object
streamResponse.Close();
streamRead.Close();
// Release the HttpWebResponse
response.Close();
allDone.Set();
}
}
I am trying to use the following code, but it does not work. Can anyone help me out on this?
Thanks in advance -Peng
return (from request in
Observable.Return((HttpWebRequest)WebRequest.Create(new Uri(postUrl))).Catch(Observable.Empty<HttpWebRequest>())
.Do(req =>
{
// Set up the request properties
req.Method = "POST";
req.ContentType = contentType;
req.UserAgent = userAgent;
req.CookieContainer = new CookieContainer();
Observable.FromAsyncPattern<Stream>(req.BeginGetRequestStream, req.EndGetRequestStream)()
.ObserveOnDispatcher()
.Subscribe(stream =>
{
stream.Write(formData, 0,
formData.Length);
stream.Close();
})
;
})
from response in
Observable.FromAsyncPattern<WebResponse>(request.BeginGetResponse, request.EndGetResponse)().Catch(Observable.Empty<WebResponse>())
from item in GetPostResponse(response.GetResponseStream()).ToObservable().Catch(Observable.Empty<string>())
select item).ObserveOnDispatcher();
Edit: To make it clear, I want to use the rx to implement the same logic in MSDN example.
in the MSDN example, it seems it first makes async call to write RequestStream, and then in the GetRequestStreamCallback, fires another async call to get the response.
Using Rx, I am able to create 2 observables
1. Observable.FromAsyncPattern(request.BeginGetRequestStream, request.EndGetRequestStream)()
2. Observable.FromAsyncPattern(request.BeginGetResponse, request.EndGetResponse)()
The problem is the second observable depends on the first one's result, so how can I do this in Rx?
In the first observable's subcribe method to create the seond observable? is it the good way?
This is how I am doing it. I configure the two Async patters up front, then use SelectMany to chain them together.
I have cut out the error handling etc from this code to keep it simple and show only the bare minimum to get it working. You should append a .Catch() similar to your own code, and if you want to get more than just a string out (say the response code) then you'll need to create a class/struct to hold all the bits of data you need and return that instead.
public IObservable<string> BeginPost(Uri uri, string postData) {
var request = HttpWebRequest.CreateHttp(uri);
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
var fetchRequestStream = Observable.FromAsyncPattern<Stream>(request.BeginGetRequestStream, request.EndGetRequestStream);
var fetchResponse = Observable.FromAsyncPattern<WebResponse>(request.BeginGetResponse, request.EndGetResponse);
return fetchRequestStream().SelectMany(stream => {
using (var writer = new StreamWriter(stream)) writer.Write(postData);
return fetchResponse();
}).Select(result => {
var response = (HttpWebResponse)result;
string s = "";
if (response.StatusCode == HttpStatusCode.OK) {
using (var reader = new StreamReader(response.GetResponseStream())) s = reader.ReadToEnd();
}
return s;
});
}
Your problem is your use of Do() here, you need to move the GetRequestStream into your SelectMany (into your "from bla in, from bla in"...), since it only makes sense to get the response stream after you've written the full request. Right now, you're trying to do both concurrently.
I have a method that performs Http POST, and since I'm using HttpWebRequest to perform it, the method relies on asynchronous calls. Since I need my method to return the response code of my Http POST, I want to make my method asynchronous. How do I do this?
I was thinking of using Dispatcher.
EDIT: So a basic outline of the structure of my code looks like this:
string response;
string httpPost(){
HttpWebRequest.BeginGetRequestStream(new AsyncCallback(requestCallback), httpWebRequest);
return response;
}
void requestCallback(IAsyncResult asyncResult){
HttpWebRequest.EndGetRequestStream(asyncResult);
HttpWebRequest.BeginGetResponse(new AsyncCallback(responseCallback), httpWebRequest);
}
void responseCallback(IAsyncResult asyncResult){
HttpWebResponse webResponse = (HttpWebResponse) HttpWebRequest.EndGetResponse(asyncResult);
response = webResponse.StatusCode.ToString();
}
I want to change httpPost() to an asynchronous method.
EDIT2:
public static void httpPost(Action<string> completed)
{
HttpWebRequest.BeginGetRequestStream(new AsyncCallback(requestCallback), httpWebRequest);
completed(HttpEngine.response);
}
On WP7, HTTPWebRequest will already be asynchronous - for an example of its use, see this code from http://www.rudigrobler.net/blog/wp7-webclient-vs-httpwebrequest
public void DoThePost(Action<string> onSuccess)
{
var request = (HttpWebRequest)WebRequest.Create(new Uri("http://www.sherdog.com/rss/news.xml"));
request.BeginGetResponse(r =>
{
var httpRequest = (HttpWebRequest)r.AsyncState;
var httpResponse = (HttpWebResponse)httpRequest.EndGetResponse(r);
using (var reader = new StreamReader(httpResponse.GetResponseStream()))
{
var response = reader.ReadToEnd();
Deployment.Current.Dispatcher.BeginInvoke(new Action(() =>
{
onSuccess(response);
}));
}
}, request);
}
Called with:
DoPost((responseText) => { responseTextBlock.Text = responseText;});