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Unexpected behavior in async method

I am currently experiencing some unexpected/unwanted behavior with an aync method I am trying to use. The async method is RecognizeAsync. I am unabled to await this method since it returns void. What is happening, is that ProcessAudio method will be called first and will seemingly run to completion however the webpage never returns my "Contact" view as it should or errors out. After the method runs to completion, the breakpoints in my handlers start being hit. If I let it play through to completion, no redirect will ever happen- in the network tab in chrome debugger, the "status" will stay marked as pending and just hang there. I believe my issue is being caused by issues with asynchronousity but have been unable to found out what exactly it is.
All help is appreciated.
[HttpPost]
public async Task<ActionResult> ProcessAudio()
{
SpeechRecognitionEngine speechEngine = new SpeechRecognitionEngine();
speechEngine.SetInputToWaveFile(Server.MapPath("~/Content/AudioAssets/speechSample.wav"));
var grammar = new DictationGrammar();
speechEngine.LoadGrammar(grammar);
speechEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(SpeechRecognizedHandler);
speechEngine.SpeechHypothesized += new EventHandler<SpeechHypothesizedEventArgs>(SpeechHypothesizedHandler);
speechEngine.RecognizeAsync(RecognizeMode.Multiple);
return View("Contact", vm); //first breakpoint hit occurs on this line
//but it doesnt seem to be executed?
}
private void SpeechRecognizedHandler(object sender, EventArgs e)
{
//do some work
//3rd breakpoint is hit here
}
private void SpeechHypothesizedHandler(object sender, EventArgs e)
{
//do some different work
//2nd breakpoint is hit here
}
UPDATE: based on suggestions, I have changed my code to (in ProcessAudio):
using (speechEngine)
{
speechEngine.SetInputToWaveFile(Server.MapPath("~/Content/AudioAssets/speechSample.wav"));
var grammar = new DictationGrammar();
speechEngine.LoadGrammar(grammar);
speechEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(SpeechRecognizedHandler);
speechEngine.SpeechHypothesized += new EventHandler<SpeechHypothesizedEventArgs>(SpeechHypothesizedHandler);
var tcsRecognized = new TaskCompletionSource<EventArgs>();
speechEngine.RecognizeCompleted += (sender, eventArgs) => tcsRecognized.SetResult(eventArgs);
speechEngine.RecognizeAsync(RecognizeMode.Multiple);
try
{
var eventArgsRecognized = await tcsRecognized.Task;
}
catch(Exception e)
{
throw (e);
}
}
and this is resulting in some wrong behavior:
The return View("Contact",vm) breakpoint will now be hit AFTER the handlers are finished firing however there is still no redirect that ever happens. I am never directed to my Contact page. I just si ton my original page indefinitely just like before.

You're going too early. The speech engine probably hasn't even started by the time you hit the return View line.
You need to wait until the final event is fired from the speech engine. The best approach would be to convert from the event based asynchrony to TAP-based asynchrony.
This can be achieved by using TaskCompletionSource<T>
Let's deal with (what I believe) should be the last event to fire after speechEngine.RecognizeAsync is called, i.e. SpeechRecognized. I'm assuming that this is the event that fires when the final result has been calculated by the speech engine.
So, first:
var tcs = new TaskCompletionSource<EventArgs>();
now lets hook it up to complete when SpeechRecognized is fired, using inline lambda-style method declaration:
speechEngine.SpeechRecognized += (sender, eventArgs) => tcs.SetResult(eventArgs);
(...wait... what happens if no speech was recognized? We'll also need to hook up the SpeechRecognitionRejected event and define a custom Exception subclass for this type of event... here I'll just call it RecognitionFailedException. Now we're trapping all possible outcomes of the recognition process, so we would hope that the TaskCompletionSource would complete in all outcomes.)
speechEngine.SpeechRecognitionRejected += (sender, eventArgs) =>
tcs.SetException(new RecognitionFailedException());
then
speechEngine.RecognizeAsync(RecognizeMode.Multiple);
now, we can await the Task property of our TaskCompletionSource:
try
{
var eventArgs = await tcs.Task;
}
catch(RecognitionFailedException ex)
{
//this would signal that nothing was recognized
}
do some processing on the EventArgs that is the Task's result, and return a viable result back to the client.
In the process of doing this, you are creating IDisposable instances that will need to be properly disposed.
So:
using(SpeechRecognitionEngine speechEngine = new SpeechRecognitionEngine())
{
//use the speechEngine with TaskCompletionSource
//wait until it's finished
try
{
var eventArgs = await tcs.Task;
}
catch(RecognitionFailedException ex)
{
//this would signal that nothing was recognized
}
} //dispose

if anyone is curious- i solved my issue by doing the following:
I changed to using Recognize() instead of RecognizeAsync(..) which lead to InvalidOperationException due to async events trying to be executed at an "invalid time in the pages lifecycle". To overcome this, I wrapped my operations in a thread and joined the thread back to the main thread directly after running it. Code below:
using (speechEngine)
{
var t = new Thread(() =>
{
speechEngine.SetInputToWaveFile(#"C:\AudioAssets\speechSample.wav");
speechEngine.LoadGrammar(dictationGrammar);
speechEngine.SpeechRecognized += new EventHandler<SpeechRecognizedEventArgs>(SpeechRecognizedHandler);
speechEngine.SpeechHypothesized += new EventHandler<SpeechHypothesizedEventArgs>(SpeechHypothesizedHandler);
speechEngine.Recognize();
});
t.Start();
t.Join();
}
}

How to detect call hang up in windows phone 10

I want to programmatically detect when call hang up in UWP app for windows phone 10.
I see Caller ID sample and see Communication blocking and filtering sample too.
But I don't find simple solution for detect when call hang up. I found CallHistoryChanged trigger and I think my complex solution is read call history when call history changed trigger and get last incoming call.
Is there any simple solution for detect call hang up?
Is my solution is correct?
Is there a better solution than my solution?

Is there any simple solution for detect call hang up?
Is my solution is correct? Is there a better solution than my solution?
As far as I know, there is no other simple solution for detect calls' hang up.
There is an event PhoneCallManager.CallStateChanged, which can also detect hang up like below:
private bool callCame = false;
PhoneCallManager.CallStateChanged += PhoneCallManager_CallStateChanged;
private async void PhoneCallManager_CallStateChanged(object sender, object e)
{
if (callCame&&(!PhoneCallManager.IsCallActive))
{
//do something
}
if (PhoneCallManager.IsCallIncoming)
{
callCame = true;
}
}
But I don't think it's better than CallHistoryChanged trigger. And it won't get you the last Hang up phone's number either.
Is my solution is correct?
So yes, your solution is correct.
Update: There is no trick here. Register the BackgroundTask:
private void btnClick_Click(object sender, RoutedEventArgs e)
{
var taskRegistered = false;
var exampleTaskName = "MyBackgroundTask";
foreach (var task in BackgroundTaskRegistration.AllTasks)
{
if (task.Value.Name == exampleTaskName)
{
taskRegistered = true;
break;
}
}
if (!taskRegistered)
{
var builder = new BackgroundTaskBuilder();
builder.Name = exampleTaskName;
builder.TaskEntryPoint = "PhoneCallBackground.Class1";
builder.SetTrigger(new PhoneTrigger(Windows.ApplicationModel.Calls.Background.PhoneTriggerType.CallHistoryChanged, false));
builder.Register();
}
}
And don't forget to register it in the appxmanifest file:
The Run Method will be fired after you hang up, if you registered the BackgroundTask. PhoneCallManager can not be registered for BackgroundTask. You need to set it as the default PhoneCall App, if you want to use this.
Update2:
I checked the demo, you are still using PhoneTriggerType.CallOriginDataRequest to register the background task. Please change it to PhoneTriggerType.CallHistoryChanged. And also make sure the registered background task is unregistered after you making any change to your codes.
Here is the demo that I modified: CallHistoryChangeTest.

Trying to make method wait for internal event handling finished

I'm new in C# async/await and facing some issues while trying to work with async method.
I have a collection:
private IList<IContactInfo> _contactInfoList
And an async method:
public async Task<IList<IContactInfo>> SelectContacts()
{
_contactInfoList = new List<IContactInfo>();
ContactsSelector selector = new ContactsSelector();
selector.ShowPicker();
selector.ContactsSelected += (object sender, ContactsSelectorEventArgs e) =>
{
this._contactInfoList = e.Contacts;
};
return _contactInfoList;
}
Contact selector is a popup user control which allows to select some contacts from phone and after the "OK" button tapped it fires ContactsSelected event. I need to get the selected contacts list from the event arguments e.Contacts and return that list in above mentioned SelectContacts() async method. And here is the issue: My method is already returning empty list _contactInfoList before the ContactsSelected event has finished his job. I know that async/await even doesn't matter in this case and this issue will be exist in usual method, but I just need to make that method to wait event handling result.

What you need to do here is convert an event style of asynchronous programming to a task style of asynchronous programming. The use of a TaskCompletionSource make this fairly straightforward.
public static Task<IList<IContactInfo>> WhenContactsSelected(
this ContactsSelector selector)
{
var tcs = new TaskCompletionSource<IList<IContactInfo>>();
selector.ContactsSelected += (object sender, ContactsSelectorEventArgs e) =>
{
tcs.TrySetResult(e.Contacts);
};
return tcs.Task;
}
Now that we have a method that returns a task with the result that we need, the method that uses it is quite straightforward:
public Task<IList<IContactInfo>> SelectContacts()
{
ContactsSelector selector = new ContactsSelector();
selector.ShowPicker();
return selector.WhenContactsSelected();
}
There are a few things to note here. First, I removed the instance field; that seems like a bad idea here. If SelectContacts is called several times it would result in the two fighting over that field. Logically if you do need to store the list it should be a local variable. Next, there are no await uses here, so the method shouldn't be marked as async. If you wanted to await the call to WhenContactsSelected then feel free to add async back in, but as of now I see no real need for it.

How to update TextBlock when async HttpRequest is finished?

I'm working on an app and I'm restructuring my code.
On my MainPage.xaml.cs I have a TextBlock and a ListBox. I have separate file (Info.cs) that handles the HttpRequest to get the information that I need to load.
The HttpRequest in Info.cs gets information from a weather API. When it gets all the information it puts the info in a ObservableCollection.. This ObservableCollection is bind to the ListBox.
Now, I'd like to update the TextBlock when the HttpRequest is finished, to show the user that all the information has been loaded.
How can I achieve this?
MainPage.xaml.cs:
WeatherInfo weatherInfo = new WeatherInfo();
weatherInfo.getTheWeatherData();
DataContext = weatherInfo;
WeatherListBox.ItemsSource = weatherInfo.ForecastList;
StatusTextBlock.Text = "Done.";
In the Info.cs I have a Dispatcher to fill the ForecastList:
Deployment.Current.Dispatcher.BeginInvoke(() =>
{
ForecastList.Clear();
ForecastList = outputList;
}
What happens now is that the TextBlock instantly changes to "Done!" (doh, its Async!) but how can I change this? So it 'waits' on the ListBox to be updated? Unfortunatly there is no 'ItemsSourceChanged' event in Windows Phone.

I suggest to use the new async+await power from C# 5.0, This is actually a good practice to use async programming in WP8.
assuming you have control of getTheWeatherData() method, and that you can mark it as async method that returns Task, you will be able to call it using await modifier.
await will not block the UI, and will cause the next code lines to be executed only after the task is done.
WeatherInfo weatherInfo = new WeatherInfo();
await weatherInfo.getTheWeatherData();
DataContext = weatherInfo;
WeatherListBox.ItemsSource = weatherInfo.ForecastList;
StatusTextBlock.Text = "Done.";
Edit:
It is supported on WP 8, and on WP 7.5 through Microsoft.Bcl.Async Nuget Package
If async programming is not an option,
you can always create a callback event in WeatherInfo class that will be signaled inside getTheWeatherData(), and register to it on the UI.
One option looks as follows:
public static void DoWork(Action processAction)
{
// do work
if (processAction != null)
processAction();
}
public static void Main()
{
// using anonymous delegate
DoWork(delegate() { Console.WriteLine("Completed"); });
// using Lambda
DoWork(() => Console.WriteLine("Completed"));
}
Both DoWork() calls will end with calling the callback that is passed as a parameter.

The calling thread cannot access this object because a different thread owns it

Ok, my current code is work in progress and probably I will try to do the same thing with the Async CTP. But I will still like to understand whats happening.
I have a function like below
// In MainWindow.xaml.cs
Task.Factory.StartNew(() => helper.Send());
// In class HttpHelper
public void Send()
{
// ...
try
{
Status = Statuses.Uploading;
// write to request stream
Status = Statuses.Downloading;
// write to response stream
Status = Statuses.Idle; // the exception is thrown here
// ...
}
catch (Exception e)
{
// ...
}
}
Full Code for HttpHelper #pastebin. Send() on line 76
I wonder why I get the exception? Maybe I did something wrong with the threading, but why is the exception raised only after I successfully set the Status property 2 times?
UPDATE: The Cause ...
I had an event handler, listening to the StatusChanged event, in 1 if clause, I forgot to use the UI thread to update the UI
helper.StatusChanged += (s, evt) =>
{
_dispatcher.Invoke(new Action(() => txtStatus.Text = helper.Status.ToString())); // I used _dispatcher here correctly
if (helper.Status == HttpHelper.Statuses.Idle || helper.Status == HttpHelper.Statuses.Error)
progBar.IsIndeterminate = false; // but not here
};

Update: I missed the (in my defense, small) comment in your code that gave away that you're using WPF/Silverlight and not Windows Forms.
Still, looks like you were able to take the basic gist of what I said and apply it to your own scenario properly (using Dispatcher.Invoke rather than Control.Invoke)—well done ;)
I'm guessing an event handler attached to your StatusChanged event updates a StatusLabel control on your UI? If that's the case, then you need to Invoke that call from the UI thread; e.g.:
void HttpHelper_StatusChanged(object sender, EventArgs e)
{
var httpHelper = (HttpHelper)sender;
UpdateStatus(httpHelper.Status);
}
void UpdateStatus(HttpHelper.Statuses status)
{
if (InvokeRequired)
{
Invoke(new Action<HttpHelper.Statuses>(UpdateStatus), status);
}
else
{
// Your code probably doesn't look like this;
// it's just an example.
statusLabel.Text = status.ToString();
}
}
The reason you might see two successes followed by a failure is a bit beyond me; but I know that the StatusLabel control in particular can be a bit evasive when it comes to threading issues. I have seen code where it is updated directly from background threads (typically due to developer obliviousness) without any exception; it looks to me like you just got lucky twice and unlucky once.

Does Status touch the UI? Because it seems like it.
I can only guess but I imagine Status changes something on UI which needs to be done through Dispatcher.Invoke().

if Status is a global variable you will get this exception becuase multiple threads are accessing and updating it at the same time. i suggest to use a lock around it