异步方法中出现意外行为

Question

我目前正在使用我尝试使用的aync方法遇到一些意外/不需要的行为.异步方法是RecognizeAsync.我无法等待此方法,因为它返回void.发生了什么,是该ProcessAudio方法将首先被调用,并且似乎将完成,但网页永远不会返回我的"联系"视图,因为它应该或错误.方法运行完成后,我的处理程序中的断点开始被击中.如果我让它完成,完成后不会发生重定向 - 在chrome调试器的网络选项卡中,"status"将保持标记为挂起并挂起.我相信我的问题是由异步性问题引起的,但却无法确定它究竟是什么.

所有帮助表示赞赏.

[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
}

更新:根据建议,我已将我的代码更改为(在ProcessAudio中):

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);
    }
}

这导致了一些错误的行为:return View("Contact",vm)现在在处理程序完成触发后会触发断点但是仍然没有发生重定向.我从未被定向到我的联系页面.我就像以前一样无限期地使用原始页面.

Answer 1

你太早了.当你上return View线时,语音引擎可能还没有开始.

您需要等到语音引擎触发最终事件.最好的方法是从基于事件的异步转换为基于TAP的异步.

这可以通过使用来实现 TaskCompletionSource<T>

让我们处理(我相信)应该是speechEngine.RecognizeAsync被调用后的最后一个事件,即SpeechRecognized.我假设这是在语音引擎计算最终结果时触发的事件.

所以,首先:

var tcs = new TaskCompletionSource<EventArgs>();

现在让我们SpeechRecognized使用内联lambda样式的方法声明将它挂起以在触发时完成:

speechEngine.SpeechRecognized += (sender, eventArgs) => tcs.SetResult(eventArgs);

(...等等......如果没有识别出语音会发生什么？我们还需要连接SpeechRecognitionRejected事件并为这种类型的事件定义一个自定义的Exception子类......这里我只是称之为RecognitionFailedException.现在我们正在捕捉识别过程的所有可能结果,因此我们希望TaskCompletionSource所有结果都能完成.)

speechEngine.SpeechRecognitionRejected += (sender, eventArgs) => 
                            tcs.SetException(new RecognitionFailedException());

然后

speechEngine.RecognizeAsync(RecognizeMode.Multiple);

现在,我们可以获得我们await的Task财产TaskCompletionSource:

try
{
    var eventArgs = await tcs.Task;
}
catch(RecognitionFailedException ex)
{
    //this would signal that nothing was recognized
}

对作为Task的结果的EventArgs进行一些处理,并将可行的结果返回给客户端.

在执行此操作的过程中,您将创建IDisposable需要正确处理的实例.

所以:

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