I have wrote this code:
private void button1_Click(object sender, RoutedEventArgs e)
{
HttpWebRequest request = SendRequests.CreateRequest(serverTextBox.Text);
IAsyncResult result = request.BeginGetResponse(new AsyncCallback(ReadWebRequestCallback), request);
}
private void ReadWebRequestCallback(IAsyncResult callbackResult)
{
HttpWebRequest myRequest = (HttpWebRequest)callbackResult.AsyncState;
try
{
HttpWebResponse myResponse = (HttpWebResponse)myRequest.EndGetResponse(callbackResult);
using (StreamReader httpwebStreamReader = new StreamReader(myResponse.GetResponseStream()))
{
string results = httpwebStreamReader.ReadToEnd();
loginValue = Parser.ParseLoginValue(results);
}
myResponse.Close();
}
catch (WebException we)
{
//
}
}
My problem at this point is that after the Click on the button I need the return value (here loginValue) of the BeginGetResponse to go on with the execution of the application.
I know that this is against the entire sense of asynchronous calls, but, there's a way to wait for the results before going on with the main thread?
Unfortunately, you have answered your own question. On Windows Phone, there is no way to do a synchronous web call.
But you don't really need to. If there is really nothing for your user to do while waiting for the response from the web, slap up a translucent overlay with a progress bar (or even better, use the global progress bar in the system try) and abide.
By contrast, if you were waiting for a synchronous call from the internet to return (which on a mobile device could take a long time), the UI would be locked and the user would think the application had hung (which, technically, is true).
Asynchronicity is your friend. Play nice with it.
Related
I'm trying to make https webAPI call, specifically - Google Directions API. Putting the uri directly inside browser gives me the result that I want, so I'm 100% sure my uri is correct.
Now, how do I call the webapi inside my PCL? Using modernhttp and HttpClient now, but am open to whatever options there are out there.
private async Task<string> GetJsonObjFromUrl(string urlRoutes)
{
HttpClient c = new HttpClient(new NativeMessageHandler());
var resp = await c.SendAsync(new HttpRequestMessage(HttpMethod.Get, new Uri(urlRoutes)));
if (resp.IsSuccessStatusCode)
{
var json = await resp.Content.ReadAsStringAsync();
return json;
}
return null;
}
What am I doing wrong?
Edit: Just putting this here because this was driving me crazy whole night. Ends up the caller way, way above forgot to put await. The execution continues straight after and never returns to get the result. That's why I never got any results... :\
The code just don't go hit anywhere below client.SendAsync / GetStringAsync
I suspect that further up your call stack, your code is calling Result / Wait / GetAwaiter().GetResult() on a task. If called from a UI thread, this will deadlock, as I explain on my blog.
The deadlock is caused by the async method attempting to resume on the UI context, but the UI thread is blocked waiting for the task to complete. Since the async method must complete in order to complete its task, there's a deadlock.
The proper fix is to replace that Result / Wait with await.
In your PCL use:
HttpClient httpClient = new HttpClient();
var json = await httpClient.GetStringAsync(Url);
In case of using HTTPS.
In Android, your main activity:
protected override void OnCreate(Bundle bundle)
{
ServicePointManager.ServerCertificateValidationCallback +=(sender, cert, chain, sslPolicyErrors) => true;
}
In iOS, in your AppDelegate:
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
ServicePointManager.ServerCertificateValidationCallback += (sender, cert, chain, sslPolicyErrors) => true;
return base.FinishedLaunching(app, options);
}
We are using xamarin forms. After an Android or IOS device resumes from background, we are making a REST call in .net that is being triggered by a timer. The first attempt on IOS returns a "The Descriptor is not a socket" error and the Android returns a "Connection refused" error. The same code works fine in Windows. Future attempts (every few seconds) in all 3 platforms work fine. Has anyone seen this and have a fix?
Code
//app on resume event
protected async override void OnResume()
{
// Handle when your app resumes
if (MainPage is RootPage)
{
RootPage mainPage = MainPage as RootPage;
if (mainPage.Detail is NavigationPage)
{
NavigationPage nvPage = mainPage.Detail as NavigationPage;
if(nvPage.CurrentPage is ThingsPage)
{
ThingsPage thPage = nvPage.CurrentPage as ThingsPage;
thPage.TurnOnTimer();
}
}
}
}
//code on the page
public void TurnOnTimer()
{
if (viewModel != null)
{
viewModel.ContinueTimer = true;
viewModel.StartAnotherTimer();
}
}
//code in view model
public async void StartAnotherTimer()
{
while (ContinueTimer)
{
try
{
DevicesUpdate devicesUpdate = await DataSource.GetDevices(LocationID, ControllerID, lastDevicesUpdateReceivedAt);
}
catch (Exception ex)
{
}
// Update the UI (because of async/await magic, this is still in the UI thread!)
if (ContinueTimer)
{
await Task.Delay(TimeSpan.FromSeconds(3));
}
}
}
public static async Task<DevicesUpdate> GetDevices(Guid locationID, Guid controllerID, DateTime lastUpdateReceivedAt)
{
DevicesUpdate devicesUpdate = await GetLastUpdatedDevices(controllerID, lastUpdateReceivedAt);
}
//code in view model
public static async Task<DevicesUpdate> GetLastUpdatedDevices(Guid controllerID,
DateTime lastUpdate)
{
System.Net.Http.HttpClient client = new System.Net.Http.HttpClient();
string url = string.Format("http://appname.azurewebsites.net/api/devices?controllerid={1}&lastUpdate={2}"
, Constants.WebServerURL, controllerID, lastUpdate);
System.Net.Http.HttpResponseMessage response = await client.GetAsync(new Uri(url));
string result = await response.Content.ReadAsStringAsync();
if (response.IsSuccessStatusCode)
{
DevicesUpdate devices = JSONHelper.Deserialize<DevicesUpdate>(result);
return devices;
}
else
{
if (response.ReasonPhrase == "UserException")
{
throw new UserException(result);
}
else
{
//throw error because the response from rest api is not a success
throw new System.Net.Http.HttpRequestException(result);
}
}
}
You might have a few things happening here that's causing problems.
GetDevices doesn't return anything. (I hope you just left out the return for brevity sake)
You are never setting ContinueTimer to false.
What iOS version are you on? In later versions, you HAVE to use HTTPS or explicitly allow non-secure connections. This shouldn't be a problem because Azure has ssl.
If you plan on running this in the background, you need to register your app as a background process.
If you don't plan on running this in the background, you might have issues with previous attempts being ran (or still trying to execute, or just have failed) and then calling more.
What is the reason for calling the 3 second timer for the network calls? What if the call takes more than 3 seconds (then you are making duplicate calls even though the first might succeed).
If you want to make your network calls more robust, check out this Blog Post by Rob Gibbons about resilient network calls.
First thing I would do is remove it from the timer because it seems like the underlying sockets are having issues cross-thread.
I know that I cannot make a true synchronous call in Windows Phone 7. However, I'm trying to at least block the threads from processing until the async call is made or there is a timeout. I've tried the following, but it seems like my app just ignores it, abandons the call, and doesn't return back. Any ideas why?
I'm trying to update a value using a Value Converter during binding.
public ManualResetEvent _event;
public void GetSync()
{
_event = new ManualResetEvent(false);
var wc = new WebClient();
wc.OpenReadCompleted += new OpenReadCompletedEventHandler(ReadCompleted);
wc.OpenReadAsync(new Uri("My URL"));
// block until async call is complete
_event.WaitOne(5000);
}
private void ReadCompleted(object sender, OpenReadCompletedEventArgs e)
{
var serializer = new XmlSerializer(typeof(MyFormatter));
// The property below is accessed back in the Value Converter for binding
StronglyTypedObject = (StObject)serializer.Deserialize(e.Result);
_event.Set();
}
To start off with, this might be tagged as a duplicate of the following thread:
Wait for HttpWebRequest.BeginGetResponse to finish in Windows Phone 7, however, the responses in that thread did not help me get over my problem.
To begin with, I am collecting user data on the UI Thread in order to process application registration, where I also have an instance of ManualResetEvent:
private static ManualResetEvent registrationEvent = new ManualResetEvent(false);
I have another thread which handles the registration process (and includes the HttpWebRequest.BeginGetResponse() and its corresponding callback method.)
Thread t = new Thread(() => RegistrationHandler.sendRegistrationData(url));
t.Start();
Right after this call, I block the current (UI) thread with a call to
registrationEvent.WaitOne();
//Process the response, update some UI elements and navigate to a different page.
httpSessionCompleted(response);
Once the thread handling the registration process starts, I am instantiating HttpWebRequest and invoking the BeginGetResponse() method on it.
try
{
HttpWebRequest request = HttpWebRequest.CreateHttp(url);
request.Method = "POST";
request.ContentType = mimeType;
request.BeginGetResponse(new AsyncCallback(GetRequestCallback), request);
}
catch (Exception ex)
{
Console.WriteLine("Exception caught in sendData(): {0}", ex.Message);
}
Now the issue is that the callback method (code below) is never invoked, and the application just freezes. There also doesn't seem to be any exception(s) thrown either.
try
{
HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
if (request != null)
{
using (HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asyncResult))
{
using (StreamReader reader = new StreamReader(response.GetResponseStream()))
{
String result = reader.ReadToEnd();
Globals.HostResponse = result;
//Signalling the calling thread to continue execution
RegistrationPage.RegistrationEvent.Set();
}
}
}
}
catch (Exception ex)
{
Console.WriteLine("Exception caught in GetRequestCallback(): {0}", ex.Message);
}
I ideally want my application to continue from httpSessionCompleted() after the callback method finishes execution. Can someone please help me with some guidance/suggestions?
Sorry for being verbose. Thanks!
You should not block UI thread, use callback pattern instead. Look at this: Windows Phone 7 - wait for Webclient to complete . Hope this helps
I have a Action that sends a simple email:
[HttpPost, ActionName("Index")]
public ActionResult IndexPost(ContactForm contactForm)
{
if (ModelState.IsValid)
{
new EmailService().SendAsync(contactForm.Email, contactForm.Name, contactForm.Subject, contactForm.Body, true);
return RedirectToAction(MVC.Contact.Success());
}
return View(contactForm);
}
And a email service:
public void SendAsync(string fromEmail, string fromName, string subject, string body, bool isBodyHtml)
{
MailMessage mailMessage....
....
SmtpClient client = new SmtpClient(settingRepository.SmtpAddress, settingRepository.SmtpPort);
client.EnableSsl = settingRepository.SmtpSsl;
client.Credentials = new NetworkCredential(settingRepository.SmtpUserName, settingRepository.SmtpPassword);
client.SendCompleted += client_SendCompleted;
client.SendAsync(mailMessage, Tuple.Create(client, mailMessage));
}
private void client_SendCompleted(object sender, System.ComponentModel.AsyncCompletedEventArgs e)
{
Tuple<SmtpClient, MailMessage> data = (Tuple<SmtpClient, MailMessage>)e.UserState;
data.Item1.Dispose();
data.Item2.Dispose();
if (e.Error != null)
{
}
}
When I send a email, I am using Async method, then my method SendAsync return immediately, then RedirectToAction is called. But the response(in this case a redirect) isn´t sent by ASP.NET until client_SendCompleted is completed.
Here's what I'm trying to understand:
When watching the execution in Visual Studio debugger, the SendAsync returns immediately (and RedirectToAction is called), but nothing happens in the browser until email is sent?
If i put a breakpoint inside client_SendCompleted, the client stay at loading.... until I hit F5 at debugger.
This is by design. ASP.NET will automatically wait for any outstanding async work to finish before finishing the request if the async work was kicked off in a way that calls into the underlying SynchronizationContext. This is to ensure that if your async operation tries to interact with the HttpContext, HttpResponse, etc. it will still be around.
If you want to do true fire & forget, you need to wrap your call in ThreadPool.QueueUserWorkItem. This will force it to run on a new thread pool thread without going through the SynchronizationContext, so the request will then happily return.
Note however, that if for any reason the app domain were to go down while your send was still in progress (e.g. if you changed the web.config file, dropped a new file into bin, the app pool recycled, etc.) your async send would be abruptly interrupted. If you care about that, take a look at Phil Haacks WebBackgrounder for ASP.NET, which let's you queue and run background work (like sending an email) in such a way that will ensure it gracefully finishes in the case the app domain shuts down.
This is an interesting one. I've reproduced the unexpected behaviour, but I can't explain it. I'll keep digging.
Anyway the solution seems to be to queue a background thread, which kind of defeats the purpose in using SendAsync. You end up with this:
MailMessage mailMessage = new MailMessage(...);
SmtpClient client = new SmtpClient(...);
client.SendCompleted += (s, e) =>
{
client.Dispose();
mailMessage.Dispose();
};
ThreadPool.QueueUserWorkItem(o =>
client.SendAsync(mailMessage, Tuple.Create(client, mailMessage)));
Which may as well become:
ThreadPool.QueueUserWorkItem(o => {
using (SmtpClient client = new SmtpClient(...))
{
using (MailMessage mailMessage = new MailMessage(...))
{
client.Send(mailMessage, Tuple.Create(client, mailMessage));
}
}
});
With .Net 4.5.2, you can do this with ActionMailer.Net:
var mailer = new MailController();
var msg = mailer.SomeMailAction(recipient);
var tcs = new TaskCompletionSource<MailMessage>();
mailer.OnMailSentCallback = tcs.SetResult;
HostingEnvironment.QueueBackgroundWorkItem(async ct =>
{
msg.DeliverAsync();
await tcs.Task;
Trace.TraceInformation("Mail sent to " + recipient);
});
Please read this first: http://www.hanselman.com/blog/HowToRunBackgroundTasksInASPNET.aspx
I sent the bug to Microsoft Connect https://connect.microsoft.com/VisualStudio/feedback/details/688210/smtpclient-sendasync-blocking-my-asp-net-mvc-request