How to wait for speech recognition callback

Question

How to wait for speech recognition callback

Brian Erickson 346

I've got the Android speech recognition stuff working well but have a question.

I've got a method called StartListening(). It's starts the speech recognition mechanism and when the OnResult call back gets fired the caller is notified via an event notification.

Now, what I'd like is a method call Listen. It should return a string consisting of the words spoken by the user. The best I've been able to come with is:

      async public Task<string> Listen()
      {
         Words = null;
         GlobalVariables.SpokenWords.SpokenWordsEvent += SpokenWordsEventHandler;
         Device.BeginInvokeOnMainThread(() =>
         {
            StartListening();
         });

         while (Words == null)
            await Task.Delay(100);

         GlobalVariables.SpokenWords.SpokenWordsEvent -= SpokenWordsEventHandler;

         return (Words);
      }

It does work but is very ugly. I'm sure there's a better way but I don't see it...any help? It would be ideal if it was not marked async...

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Answer 1

Cole Xia (Shanghai Wicresoft Co,.Ltd.) 6,756

Hello,

Welcome to Microsoft Q&A!

Take a look at TaskCompletionSource , It enables the creation of a task that can be handed out to consumers.

Sample

   public Task<string> MyTask()  
   {  
     
       var tcs = new TaskCompletionSource<string>();  
     
       {  
           //OnResult call back  
           tcs.SetResult(Words);  
       }  
     
       return tcs.Task;  
     
   }

BTW , I would suggest you use official sample for SpeechToText.

We could handle the callback in OnActivityResult method in activity.

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Brian Erickson 346

There's something I'm not understanding... This just hangs as result is never set because listening never starts.

 async public Task<string> Listen()
          {
             string Words;
             GlobalVariables.SpokenWords.SpokenWordsEvent += SpokenWordsEventHandler;
             ListenResult = new TaskCompletionSource<string>();

             Device.BeginInvokeOnMainThread(() =>
             {
               StartListening();
             });

             Words = ListenResult.Task.Result;

             //while (Words == null)
             //   await Task.Delay(100);

             ListenResult = null;
             GlobalVariables.SpokenWords.SpokenWordsEvent -= SpokenWordsEventHandler;

             return (Words);
          }

Brian Erickson 346 Reputation points

2021-03-15T14:18:16.127+00:00

FWIW, the speech to text is performed in a foreground service and is loosely based on the sample. I used event notifications as that mechanism works for UWP as well.
Cole Xia (Shanghai Wicresoft Co,.Ltd.) 6,756 Reputation points

2021-03-16T02:17:26.073+00:00

Could you post the code in SpokenWordsEventHandler ?
Brian Erickson 346 Reputation points

2021-03-16T13:53:55.077+00:00

This appears to be helpful when getting results from a task in a different thread. Just hangs if things are in the same thread. I'll stick with my delay loop.
Brian Erickson 346 Reputation points

2021-03-16T13:57:41.627+00:00

Here it is...
private void SpokenWordsEventHandler(object sender, SpokenWordsEventArgs e)
{
if (e.Error == 0)
{
if (ListenResult != null)
ListenResult.SetResult(e.Words);
Words = e.Words;
}
else
{
Device.BeginInvokeOnMainThread(() =>
{
StartListening();
});
}
}

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How to wait for speech recognition callback

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